THE Comet was well seen here on Monday, October 23, for some considerable time about 5 a.m., though clouds occasionally hid part of it. I noticed the following -1. The length that was clearly visible was such, that if the head had been placed on Sirius, the tail would have reached to Orion's belt. 2. The lower edge of the tail was comparatively sharp and brightly defined, while there was 10 well-defined upper edge. 3. At first sight the tail ended, fairly abruptly, in a short fork. But on glancing to one side, so as to allow the image to fall on a more sensitive part of the retina, one became aware that these two forks were continued in a very faint and hazy manner as far again as the length of the comet first noticed (mentioned and measured in (1.)) Or, more strictly, one became aware of a black rift in the sky behind the comet, in its direction, above and below which the sky was faintly luminous. One may say that at first sight the comet ended like a house-martin's, on more careful observation like a swallow's, tail. The total length of the comet thus seen was enormous; and the appearance suggested an even greater extension. W. LARDEN

Cheltenham, October 24

ALTHOUGH the fact is mentioned in NATURE of the 5th inst., that the comet was observed by Mr. Finlay, the Fir t Assistant to the Astronomer-Royal at the Cape of Good Hope, at 5 a.m. on September 8, perhaps the illowing graphic account of its appearance, which 1 extract from a letter received this morning from my friend Mr. G. B. Bennett, dated Water-Hof, Cape Town, September 26, may have some interest. Mr. Bennett believed himself the earliest observer, but he does not consider the comet more conspicuous on this occasion than it was in 1843.

"I take an especial intere t in our present visitor, as I fancy that I am the very first person who saw it, and this was on the 8th inst. at 5 a.m. I was attracted into the garden by the marvellous brilliancy of the stars. On turning my eyes ea tward I detected a stranger at once; it did not appear as a comer, but I knew that there ought not to be any large star in the spot occupied. It was ab ut midway between Alpherat (Cor Hydræ) and Regulus; the latter, however, was not visible at the time I called to my daughter, and asked her to put her head out of the window, and she at once said, 'a comet.' I then wrote a note to the Editor of the Cape Times announcing it; this letter did not reach him, it would be long to explain why. . . . It is of such size and brilliancy as to be seen in the brightest sunshine. I saw it September 18 between noon and I p.m. Dr. Gill is reported to have said, the largest for 200 years.' I don't believe he said so; if so, he could not have seen the one of March, 1843."

My friend adds that he has ascertained most po itively that it was not observed from the deck of either of the mail steamers Athenian or Garth Castle, then approaching the Cape. The latter carried Father Perry and the members of the Transit of Venus Expedition. "My belief is that it came within the ken of human vision on the morning of the 8th September, and not before." His station of observation, Waterhof, is about half-way up Table Mountain. J. II. LEFROY

October 19

REFERRING to my letter of the 16th, I beg to say that the R.A. of the neighbouring object" should have been Ioh. IIm., and that it was probably, not Schmidt's comet, as supp sed, but the 7th or 8th mag. star 19980 Lalande, which does not appear in the B. A. Catalogue, or in the V.S. Catalogue, or in the large maps of the S.D.V.K., or on Mattly's Globe. It appeared to me of much greater magnitude than the above. Bray, Co. Wicklow, Cctober 21

WENTWORTH ERCK

THE magnificent comet now visible in our eastern sky shortly before sunrise is no doubt being observed in England. In case it should not I may add that its approximate position at 4h. 50m. a.m. (local mean time) this morning as determined by my equatorially mounted (44 inch Cooke) tele cope was R.A. 10h. 55m., South declination 3° 29'. The tail by estimation is about 14°, and of unusual breadth. The borders of the tail appear much brighter than the central part. H COLLETT

Lahore, The Punjab, India, September 25

The Proposed Bridge over the Forth

IT is no small evidence of the importance of this great undertaking, that the proposed scheme should have drawn from Sir

George Biddell Airy such severe criticism as that which appeared in last week's NATURE. Coming from such a source, this criticism is sure, not only to receive the most careful consideration of those few who are sufficiently conversant with such matters to form their own opinion, but is sure to have great weight with the much larger class who accept the opinion of those they conceive best able to judge. It therefore behoves those who are responsible for this scheme, to make the best answer they can. Whether they will be able to remove altogether the impression adverse to the scheme, may well be doubted; but for my own part I do not anticipate that they will find much difficulty in meeting the objections raised, in so far as these are definite. It is not my pre ent object to defend, or even to discuss the merits of the proposed bridge; what I wish to point out is that the knowledge of engineers as regards the theory of structures, is not sim erfect, or their methods of designing such guesswork as might be inferred from the tone of the criticism.

Sir George Biddell Airy expre ses alarm lest in the design due consideration has not been paid to the "theory of buckling;" but whether this is so or not, does not appear from any circumstance to which he has referred.

To make a strut or "thrust-bar" 340 feet long to sustain a thrust of several hundred tons, is doubtless a stupendous undertaking, but so is a bridge to carry a railway over 1700 feet. There is, however, no theoretical reason again t the possibility of such tructures; that is to say, assuming the same strength and elastic properties of material as are experienced in existing structures, it appears by the application of the principles of mechanics that both such distributions and uch quantities of material are possible as will assure the safety of these structures. Whether or not such distribution and quantities have been secured in the de igns for these struts, could only be judged of after careful consideration of the proposed lateral sections in conjunction with the longitudinal section, and to these no reference whatever is made in the critici-m.

That the experienced engineers who have made themselves responsible for this design con have overlooked such an important consideration asuckling is very improbable. There is no possible accident to structures which has received more careful consideration than buckling, or of which the laws have been more definitely ascertained.

The very pretty method, given in the appendix to the communication under consideration, for obtaining the formula WC? is a well-known application of the theory of elasti

πο

a2

city, and is given by Bresse.1 But this formula is known only to apply to prismatic bars very thin, compared with their length, and is therefore of little practical use. The laws of stiffness and s'rength for s'ruts of a solid section, were first deduced by Eaton Hodgkinson from his own experiments, and have since been extended to struts of any section by Lewis Gordon a d Rankine. For wrought iron, putting P for the load, S the area of section, the length, and the least radius of gyration of the section about any line in that section, the units being inches and lbs., the formula is

From this it will be seen that I must be very large compared with before this formula assumes the same form as that which Sir George Biddell Airy has obtained.

Such general formulæ are not, however, the only or the chief guides i modern construction; sufficient actual experience has been obtained as regard, uch a great variety of forms for the elementary parts of structures as to furnish rules for the proportioning of every class. And 1hough any n velty such as unprecedented size furni hes matter for grave consideration, both as regards proportions and the pos-ibilities of art, still the theory and data for assuring reasonable safety are available, and engineers must be much behind the day if they neglect these. Owens College, October 21 OSBORNE REYNOLDS

sa ne difficulties as Sir George Airy, I propose with your permission to offer a few explanations.

Sir G. Airy summarises his remarks under six heads, but I think two would have sufficed, viz. that the bridge was too big to please Sir George, and that the engineers were presumably incompetent. As to size, for example, Sir George considers the fact of the cantilever being "longer than the Cathedral by 175 feet is in itself enough to excite some fear," and even to "justify great alarm." But when I look for some justification for this bold statement I find that Sir George does not advance any reason whatever, nor make use in any way of his high mathe matical attainments, but simply shifts the responsibility for this alarm on to the shoulders of the "citizens of London," asking, "would they feel themselves in perfect security? I think not; and I claim the same privilege of entertaining the sense of insecurity for the proposed Forth Bridge.'

If Sir George had alleged that the stresses on the cantilever could not be calculated, or that the strength of the steel ties and struts could not be predicted, or that the cantilever could not be erected, I might have replied by publishing diagrams of stresses, results of experiments, and the names of the firms who have tendered for the work. I cannot, however, answer an argument based upon the supposed fears of the "citizens of London." To prove that Sir George's criticisms imply a charge of incompetency on the part of the engineers, I need only point out that in one sentence he remarks that " 'experienced engineers must have known instances in which buildings have failed from want of consideration of buckling," and in another, that "there appears to be a fear of its occurrence in various parts of the bracket," when "the bridge will be ruined." Sir George's conclusions on this head are, however, as he fairly enough states, "made in the total absence of experiment or explanation," and in ignorance whether "a theory of buckling finds place in any of the books which treat of engineering.' To assume, however, that an engineer is similarly ignorant, clearly amounts to a grave charge of incompetency. Again, how incompetent must the engineer be who required to be informed that the "horizontal action of the wind on the great projecting brackets depends not simply on the wind's pressure, but also on its leverage," or who neglected to provide for the consequent stresses. Yet Sir George does not hesitate to say, in reference to this, that "in the proposed Forth bridge there is a risk of danger of the most serious kind, which may perhaps surpass all other dangers."

As Sir George in the whole of his letter does not produce a single figure or fact in support of his very serious charges, I must, in justice to Mr. Fowler and myself, explain that it was from no want of data. At Sir George's request he was furnished with every necessary detail for ascertaining the maximum stress on each member, and the factor of safety. I stated in the paper referred to by Sir George at the commencement of his letter, that under the combined action of an impossible rolling load of 3400 tons upon one span, and a hurricane of 56 lbs. per square foot, the maximum stress upon the steel would in no case exceed 7 tons per square inch. Any useful criticism must be directed to prove that such load is not enough or that such stress is too great. Nothing can be decided by appeals to the citizens of London.

Sir George's remarks about what he terms "buckling," and the "total absence of experiment," I can hardly reconcile with his having read my paper, because I have there devoted six pages to the question of long struts, and have given the results of the most recent experiments on flexure by myself and others. When he asks whether a tubular strut 340 feet long would be safe against buckling, he has evidently overlooked the twenty years' existence of the Saltash Bridge, which has a tubular arched iron strut 455 feet long, subject to higher stresses than are any of the steel struts in the proposed bridge. Reference is made to the fall of the roof of the Brunswick Theatre, which is attributed to buckling. This accident occurred about fifty-four years ago, and consequently considerably before my time; nevertheless I have heard of it often, and if I am not mistaken, the verdict of the jury was to the effect that the fall of the roof was due to a carpenter's shop weighing about twenty-five tons having been built on the tie rod, which sagged under the weight, and so pulled the feet of the principals off the wall. However that may be matters little, as engineers are in possession of more recent and trustworthy data than the personal reminiscences of Sir George Airy. American bridges invariably have long struts, and consequently there is no lack of practical experience on the subject.

The late Astronomer Royal thinks that "the proposed construction is not a safe one," and hopes to see it withdrawn. When he wrote his letter it probably did not occur to him that rival railway companies might be only too glad to seize hold of anything which might prejudice the Forth Bridge project and alarm the contractors who were preparing their tenders for the work. I do not complain of Sir George's action, as it involves a matter of taste of which he is sole judge. I would only mention that when he penned the above sentence he had been furnished by the engineers with the Parliamentary evidence and other documents necessary to inform him of the following facts (1) That a wind pressure of 448 lbs. per square foot upon the front surface would, as stated in my paper on the Forth Bridge, be "required to upset the bridge, and under this ideal pressure, though the wind bracing would, it is true, be on the point of failing, none of the great tubes or ten ion members of the main girders would even be permanently deformed." (2) From the evidence given before the Tay Bridge Commissioners, Sir George, being a witness, would know that, even supposing the workmanship had been good, a wind pressure of about one-tenth of the preceding would have sufficed to destroy the Tay Bridge. (3) He would also remember, no doubt, his own report of 1873, wherein he says that "the greatest wind pressure to which a plain surface like that of the Forth Bridge will be subjected in its whole extent is 10 lbs. per square foot." (4) The Parliamentary evidence would have informed him that the proposed design was the outcome of many months' consideration by the engineers-in-chief of the companies interested, representing a joint capital of 225 millions sterling, and that it was referred to a Special Committee of the House of Commons and to a special Committee of the Board of Trade inspecting officers for examination and report, and that the reports of engineers and committees were alike unanimous in testifying to the exceptional strength and stability of the proposed bridge. As a sample of foreign opinion, I would quote that of Mr. Clarke, the eminent American engineer and contractor, who has built more big bridges himself than are to be found in the whole of this country, and who has just completed a viaduct 301 feet in height, by far the tallest in the world. Referring to the proposed bridge, he writes: "If my opinion is of any value I wish to say that a more thoroughly practical and well considered design I have never seen." I need hardly say that the opinion of such a man has far more weight than that of an army of

amateurs.

Sir George Airy refers "unhesitatingly to the suspension bridge" as the construction which he should recommend. He has clearly learnt nothing on that head during the past ten years. In a report on the late Sir Thomas Bouch's design for the Forth Bridge on the suspension principle, dated April 9, 1873, he says: "I have no doubt of the perfect success of this bridge, and I should be proud to have my name associated with it." Chiefly on this recommendation, and in spite of numerous warnings from practical men, the bridge was commenced, but it had to be abandoned after spending many, thousands, because having reference to the fate of the Tay Bridge, it was pronounced by the Board of Trade and every engineer of experience at home and abroad to be totally unfit to carry railway trains in safety across the Forth.

Sir George Airy stands alone in his advocacy of a suspension bridge for high speed traffic, and in his views as to the force and action of the wind on such a structure. That being so I may be permitted to say that I should have felt no little misgiving if he had approved of the substituted girder bridge, because it has been the aim of Mr. Fowler and myself to design a structure of exceptional strength and rigidity, differing in every essential respect from that with which Sir George evidently would still be proud to have his name associated.

B. BAKER

THE alarming observations in Sir George Airy's paper on the stability of the Forth Bridge as proposed by Mr. Fowler, which appeared in your last issue, seem to call for a reply, and I think I am in a position to make an unbiassed reply, as I had nothing whatever to do with the design, and moreover do not approve of it. I disapprove of the adopted system as one in which the distribution of the material can be economical only in a moderate degree, and I object to it from an æsthetic point of view, and also on account of some practical reasons of minor import, but I have no hesitation in as erting that the material may be so arranged in it- and very probably is so arranged-that the sta

bility of the bridge when erected would equal that of the best existing structures of that class.

The paper referred to contains six points of objection, which are treated in a general way without attempting a scientific criticism. This is to be regretted considering the importance of the subject. I take each point in succession. With regard to

I. I cannot see an objection to the novelty of a system, if, as n this case, the conditions are unprecedented, and if the author of the paper himself is compelled to recommend a system of striking novelty.

II. What, may be asked, constitutes the enormity of magnitude of a structural part? Is it the excessive proportion of strain in it arising from its own weight to that arising from other weights and forces? If so, it will be found that this proportion may here be still very small, although it may not be ignored, as sometimes is done.

III. The experimental knowledge hitherto derived from structures with rising degrees of magnitude has not upset the theories used in the calculations of strength. It cannot be asserted that the top flange of a common rolled beam, being a strut, we assume twenty times as long as it is wide, would be under a test load in a safer position against buckling than the top flange of the Ohio girder bridge, which is 510 feet long and 20 feet wide, or the bottom flange of the Forth Bridge, which is 675 feet long and from 32 to 120 feet wide.

IV. We constantly rely on the strength of long struts; they exist in all girders, and many of them are of the same importance for the strength of the girders as the links for the strength of a chain. The theory of their strength, imperfect as it is, is applicable to all with a fair amount of truth, and there is no reason why it should not be applied equally to the struts in the Forth Bridge.

V. Assuming that the dangers from wind-pressure during the erection do not concern us here, it would be interesting to hear from the author which parts of the erected bridge would probably give way first, and whether this would take place by crushing, shearing, twisting, or pulling actions. The leverage offered to wind by the long brackets would come into question only when the pressure is different on the two sides of a pier. The difference would produce a twisting action, which would exist in the central pier, but which could be obviated in the two side piers. The resisting leverage of the central pier is 270 feet, or about two-thirds of the acting leverage. Approximately the same proportion obtains with regard to the stability against tilting under uniform wind-pressure, while in the case of the Tay Bridge the proportion was less than one-third.

VI. It is highly improbable that Mr. Baker should not have calculated his struts; in his book on the strength of beams, columns, and arches, he gives a very intelligible deduction of the theory of long struts, which, although elementary and not so elegant as that by the author, seems original. I have found deductions of that kind in most English text books, while in books of foreign origin generally the equation of the line of flexure is taken as the starting point. Its approximate form

where EI= C in the Paper. This formula is not applicable to short struts, since W might exceed the crushing strength of the material. The limiting weight W for short columns is therefore calculated with W1 = fp, where f is the sectional area and the pressure on the sectional unit. Unfortunately there exists among theorists a difference of opinion as to the proper value of ; some put for it the crushing strength, and others the limit of elasticity, and now and then there are controversies going on about this matter. Meanwhile it is impossible to mark the limit between short and long struts which theoretically exists. Practically, however, the limit is indistinct, and Rankine, Gordon, and others, taking this into consideration, have put the two formulæ together into one empirical formula for W", the limiting weight for struts of any given dimensions.

HAVING read with interest Sir G. Airy's article on this sub. ject in the last number of NATURE, I am glad to see that it advocates a suspension-bridge in lieu of the proposed structure. It may perhaps interest your readers to give the particulars of the Great International Suspension Bridge over the Niagara River, which supports a carriage-way and a railway-track above.

The length of span between the towers is 800 feet. There are 4 cables, each composed of 3640 wires No. 9=155" diam., without weld or joint; the cables are 10" in diameter. All the wires of each cable were separately brought into position, so that each one bears its full share of the tension. When a cable had been thus built up, it was tightly served with soft iron wire to bind the 3640 wires together, and to preserve them from

rust.

Since this bridge was built, great improvements have been made in the manufacture of wire. Whereas the resistance to tensile stress at the moment of fracture of the best qualities of iron wire, such as that manufactured at Manchester for this bridge, does not much exceed 27 tons per square inch of section, hardened and tempered steel wire can now be made in large quantities and in long lengths with a minimum resistance at the moment of fracture of 90 tons per square inch.

Steel plates, rods, or bars cannot be made in quantity with a higher resistance than 34 tons, or less than half that of wire. Hardened and tempered steel wire similar to that used in pianos is thus clearly the most suitable material for suspension bridges, and has been recognised as such in America, where it is to be used in the construction of the New York and Brooklyn suspension bridge, the span of which is the same as the proposed Forth Bridge.

Our English railway engineers, however, have not yet recog nised the great advantages wire possesses over any other form of material such as bars, chains, &c., for resisting tensile stress, and the further advantages that wire can be tested more easily and made of a more uniform quality.

Some ten years ago I called on Sir T. Bouch, the former Engineer to the Forth Bridge, to point out the advantages of a tempered steel wire suspension bridge over any other form. of structure for the Forth Bridge. The idea was, however, nveer worked out on paper. WILLIAM H. JOHNSON Manchester, October 23

On the Alterations in the Dimensions of the Magnetic Metals by the Act of Magnetisation

I HAVE read with interest Prof. Barrett's paper in NATURE, vol. xxvi. p. 585. Between his results as to the effect of magnetisation on the dimensions of bars of iron, of steel, and of nickel, and those of Sir William Thomson's experiments ("Electrodynamic Qualities of Metals," Part VII., Phil. Trans. R. S., Part I., 1879) on the effects of stress in the magnetisation of bars of the same metals, there exists a remarkable analogy, which, however, seems to break down in the case of cobalt. According to these experiments (which, I may mention, were carried out under Sir William Thomson's direction by my brother, Mr. Thomas Gray, and myself), the effect of the application of longitudinal pull to a bar of iron, while under the influence of inductive force tending to produce longitudinal magnetisation, is, for forces lower than a certain critical value, called from the Italian experimenter who first observed it, the Villari Critical Value, to increase, and of the removal of pull, to diminish, the inductive magnetisation. When the magnetising force exceeded the critical value, these effects changed sign, and tended to a constant value as the magnetising force was increased.

Again, the effect of transverse pull, produced by means of hydrostatic pressure in an iron tube, is, when applied, to diminish the longitudinal magnetisation, and when removed, to increase it. We see, then, from Joule's result, confirmed by

Prof. Barrett's, that the effect of longitudinally magnetising a bar of iron, or of increasing its magnetisation, is to increase its dimensions longitudinally and to diminish them laterally, so that the volume remains constant; and on the other hand, from Sir William Thomson's investigations, that the effect of increase of longitudinal dimensions in an iron bar is to increase, and of increase of transverse dimensions to diminish its longitudinal magnetisation.

This analogy holds also with reference to steel and nickel. In the case of bars of these metals, we found their longitudinal magnetisation to be diminished by the application of longitudinal pull, and Prof. Barrett has found that bars of the same metals undergo a shortening when their longitudinal magnetisation is increased.

In the case of cobalt, however, the results do not agree. The results for cobalt, given in Sir W. Thomson's paper, are somewhat anomalous, but they refer only to the effect of stress on magnetism in a bar which had been previously magnetised and then placed while being experimented on, under the influence of the earth's vertical force The results were therefore complicated by the effects of the stress on the residual magnetism. So far as these results go they bear out to some extent those found by Prof. Barrett, but further experiments, the results of which have not yet been published, prove that the effects of stres are the same as for nickel. This is the case at least for all but low magnetising forces.

The behaviour of cobalt and nickel throughout a wide range of magnetising forces, and under the influence of both transverse and longitudinal stress, will, it is hoped, be fully investigated in a continuation of Sir William Thomson's experiments, begun some time ago, and temporarily interrupted by other, and for the time being, more pressing work, but now about to be

resumed.

I may mention that my brother and nyself pointed out in NATURE, vol. xviii. p. 329, the applicability of a modification of Edison's Tasimeter to the measurement of the changes of dimensions produced in a body by magnetisation. We still think that this is perhaps the most simple method, and we have found it very sensitive for qualitative results. In our trials of it we have experienced some difficulty in obtaining a carbon button which would return after having been subjected to stress to the same resistance as before. The experiments of Prof. Mendenhall, however, show that the kind of carbon used by Edison in his Tasimeter possesses this property in perfection; and we hope soon by the use of this carbon to obtain quantitative results. ANDREW GRAY

The Physical Laboratory, the University, Glasgow,

October 19

Aurora

AN aurora was seen at Croydon at about 7 p.m. on Wednesday,

the 18th inst. Three streamers of a whitish colour could be traced distinctly across the whole of the sky while the moon was still up. A. E. EATON

The Victoria Hall Science Lectures

THE popular science lectures at the Victoria Hall have proved quite sufficiently successful, so far, to make the managers wish to continue them, provided that the kindness of competent lec. turers makes it possible to do so. There have been audiences each night of ab ut 600-small compared with what the building will hold, but not amiss for a Friday night, in a neighbourhood where (except on Saturdays) people think twice before spending a penny. Those who have been present, agree in describing the audience as a peculiar one, for whom greater simplicity is needed than for the audiences of mechanics' institutes, and the frequenters of penny science lectures in general. They are quite ready to attend and to be interested, and do not th nk an hour too long, provided the ball is kept constantly moving, but as to this they are very exacting, and any breakdown of the apparatus, however temporary, places the success of the lecture in serious danger. There are stamps and whistles of impatience at any pause, such as must occur in adjusting experiments, but these cease the moment the lecture proper proceeds. This impatience perhaps makes the sustained interest of a lantern more

suited to the audience than the more varied but intermittent

experiments.

It is to be wished these lectures could be more widely known

among the artisan class, who have not too many opportunities of hearing sound popular science. ONE OF THE COMMITTEE Royal Victoria Coffee Hall, Waterloo Road, S. E., October

THE TYPHOONS OF THE CHINESE SEAS▾

THIS work by the learned director of the Zi-Ka-Wei Observatory, consisting of 171 pages quarto, and eight illustrative plates giving the tracks of the twenty typhoons of 1881, may be regarded as the outcome of the recent establishment of meteorological stations over the regions swept by the typhoon. The typhoons of 1880, amounting to fourteen, were described by Father Dechevrens in a previous paper. These two papers, from the greater fulness and accuracy of their details, form a contribution of considerable importance to the literature of cyclones.

An examination of the tracks of these thirty-four typhoons shows that they generally have their origin in the zone comprised between the parallels of 10° and 17o, some of them originating in the Archipelago of the Philippines, but the greater number to the eastward of these islands in the Pacific. The first part of their course is westerly and north-westerly; they then recurve about the latitude of Shanghai, and thence follow a northeasterly course over Japan. During the first half of their course the barometric gradients are steepest, and the destructive energy of typhoons is most fully developed; but after advancing on the continent, and, particularly after recurving to eastward, they rapidly increase in extent, form gradients less steep, and ultimately assume the ordinary form of the cyclones of NorthWestern Europe. In illustration of the steepness of the gradients sometimes formed, it is stated that on July 15 a gradient occurred of 2.760 inches per 100 miles, or one inch to 36 miles.

Typhoons do not occur during the prevalence of the north-east monsoon from November to May. In 1881 the typhoon season extended from May 22 to November 29. In Japan the true typhoon season is restricted to August and September, the storms there during the other months resembling rather the ordinary cyclones of temperate regions. The tracks of the typhoons during the months of moderate temperature, May, June, the latter half of September, Cctober, and November, are the most southerly; they lie flattest on the parallels of latitude, and present a great concavity looking eastward; but those of the warmer months, July, August, and the beginning of September, exhibit, on the other hand, very

This seasonal difference in the form of the open curves. tracks, taken in connection with the general form of the recurving tracks of the West Indian hurricanes, which are less open than those of the Chinese seas, suggests a possible connection between the forms of these curves and the different distributions of atmospheric pressure prevailing over the continents at the time.

Of the new facts brought forward in this report, the most important perhaps are those which show that the typhoon tracks have the feature of recurvation as distinctly as the hurricanes of the West Indies and the Indian Ocean. The degree of recurvation and the relative frequency with which it occurs in the tracks of the Cyclones of the Chinese seas, the West Indies, the Indian Ocean near Madagascar, and the Bay of Bengal respectively, are important features in the history of these storms, which such reports will do much to elucidate. We shall look forward with the liveliest interest to Father Dechevrens' future reports, which from the lines of inquiry already indicated may be expected to throw considerable light on the influence of extensive regions of dry air and of moist air respectively, and of elevated

The Typhoons of the Chinese Seas in the Year 1881." By Marc Dechevrens, S. J., Director of the Zi-Ka-Wei Observatory, China. (Shanghai Kelly and Walsh, 1832.)

table-lands, in determining the continuance and the direction of the course of cyclones; and the influence of isolated mountains and mountainous ridges in breaking up a cyclone into two distinct cyclones, which, from the difficulty necessarily experienced by seamen in interpreting the complex phenomena attending them, often prove so destructive in their effects.

SEISMOLOGY IN JAPAN

THE 'HE first earthquake that I ever felt took place about 2 a.m. on the night of April 10, 1876. On this night, which was soon after my arrival in Yedo, I had been installed in a new house. To be absolutely alone in a large partially furnished dwelling in a strange land, and then in the dead of night to be wakened by a swinging motion of the bedstead, a rattling of windows, creaking of timbers, and flapping of pictures was more than bewildering.

For some time after the motion had died away, which motion had several maxima and minima, some little rings upon the bedstead which had been caused to swing, kept up a gentle clicking, and a night light upon a basin of oil as it swayed from side to side cast long flickering shadows across the room. The general behaviour of things was ghostly, and it was some time before I could assure myself that what I had experienced was an earthquake. Next morning, however, my doubts were dissipated by my neighbours making jocular inquiries about the nature of my experiences. Earthquake conversation, I may remark, is often used in Yedo to fill up the gaps in conversation, which in England are usually stopped by queries and truisms about the weather. This was my first earthquake. Palmieri's instrument indicated that its direction was about E.S.E. to W.N.W., and its force was 6 degrees. By 6 degrees is meant that the shaking caused some mercury contained in a glass tube to wash up and down until a little string attached to an iron float on its surface had turned a pully and a pointer through 6°. By observing the tables of these indications it is seen that a very gentle shaking of long duration may get up a violent oscillation in the mercury and so indicate a shock of a great number of degrees, whilst a violent sharp shock, which might knock over a chimney, may possibly only indicate a few degrees. Since my first earthquake I have had the opportunity during the last six years of studying rather more than 400 other shakings. One of these shook down chimneys, unroofed houses, twisted gravestones, and by its action generally entitled itself to be called destructive and alarming. The effect that this earthquake produced upon the nerves of many people was quite as great as that which might be produced upon children with an imaginary ghost. As residents in Japan are so often alarmed by earthquakes it is only natural that they should be led to study these phenomena. Amongst the first instruments which were employed for their investigation were, as might be anticipated, small columns, bowls of liquid, and other contrivances, which are found described in books and papers treating of observational seismology.

Columns which have been made of various shapes and various materials have been found unsatisfactory, because it is seldom (even when a house may be swaying violently), if they are on a stone platform firmly fixed to the ground that they are overturned.

When

it happens that they are overturned, if there were several columns side by side you would usually find them lying pointing like the arms of a star-fish in different directions. If an earthquake was a sharp blow, no doubt the columns would fall in the direction of the shock and also towards the point from which the shock came. Yedo earthquakes, however, commence gently, and the column is caused to rock before it falls, and as it rocks its plane of rocking may be gradually changed. Another explanation would be that some of the columns had fallen with direct shocks and some with reflected shocks, or

that some were overturned with the normal and some with the succeeding transverse vibrations.

Bowls of liquid have been found impracticable; first, because it is seldom that in a bowl on a firm foundation a sufficiently measurable amount of washing up is obtained; and second, that any of the usual methods of registering the motion as well as many other methods, both chemical and mechanical which have been tried, are not satisfactory. Also there are the difficulties of freezing and evaporation to contend with.

Similarly the records of the old-fashioned ordinary pendulum with a pointer resting in sand, or, what is perhaps better, provided with a sliding pointer writing over a smoked glass plate, are also very unsatisfactory. All that many of the carefully drawn records produced by swinging pendulums appear to indicate, is that there has been an earthquake, and it has caused the pendulum to swing about. For reasons like these, after considerable experience the conclusion arrived at is that the records of most of the older forms of seismographs and seismometers, of which legions have been experimented with, can only be regarded as being seismoscopic.

When we look into the history of observational seismology, and take the following description of a seismometer invented nearly 1800 years ago as a standard of comparison between the old and better known forms of earthquake instruments for registering ordinary shocks, it is doubtful whether this branch of earthquake investigation has been much advanced. This description was given to me by Mr. J. Hattori, vice-director of the Imperial University. It was translated for me by my assistant, Mr. M. Kuwabara. It runs as follows:

In a Chinese history called "Gokanjo," we find the following: "In the first year of Yōka (A.D. 136) a Chinese called Chioko invented a seismometer. This instrument consists of a spherically formed copper vessel (Fig. 1), its diameter being 8'shaku.' It is covered at its top. Its form resembles a wine bottle. Its outer part is ornamented with the figures of different kinds of birds and animals and old peculiar looking letters. In the inner part of this instrument a pillar is so placed that it can move in eight directions. Also in the inside of this bottle there is an arrangement by which some record of an earthquake is made according to the movement of the pillar. On the outside of the bottle there are eight dragon heads, each of which contains a ball. Underneath these heads there are eight frogs, so placed that they appear to watch the dragon's face, so that they are ready to receive the ball if it should be dropped. All the arrangements which cause the pillars when it moves to knock the ball out of the dragon's mouth are well hidden in the bottle. When an earthquake occurs and the bottle is shaken, the dragon instantly drops the ball, and the frog which receives it vibrates vigorously. Any one watching this instrument can easily observe earthquakes. With this arrangement, although one dragon may drop a ball, it is not necessary for the other seven dragons to drop their balls unless the movement has been in all directions; thus one can easily tell the direction of an earthquake. Once upon a time a dragon dropped its ball without any earthquake, and the people therefore thought that this instrument was of no use, but after two or three days a notice came saying that an earthquake had taken place in Rōsei. Hearing of this, those who did not believe about the use of this instrument began to believe in it again. After this ingenious instrument had been invented by Chiokō, the Chinese Government wisely appointed a secretary to make observations on earthquakes."

We have here I think not only an account of an earthquake instrument which in principle is identical with many of our modern inventions, but the science has been conjoined with art. The record of the Chinese Government establishing a seismological bureau at a time when America was unknown, and half of Western Europe were