extreme tenuity, others were dense and bright, hiding the stars over which they passed. The sky in the end was covered with a light haze, which condensed into a cloud canopy. No prismatic colours were visible, streamers, beams, and rays throughout being alike of a pure white light, though greatly luminous, so as to retain di. tinctive individuality in the face of brilliant moonlight. Thursday, early morn, sun shining through a hazy sky, wind light from the south; 9 a.m., overcast; II a.m., rainfall set in. Continuous all the day. Sharp fall of barometer. Thermometer mid-day, 65, wind inclined to back to the eastward. Considering that the vernal and autumnal equinoxes are the usual periods of auroral activity, and that there is yet a month to the 21st of September, an instance, now of auroral energy is somewhat out of the usual course of things. The equinoctial gales, yet earlier, set in with much rigour. Perhaps, as everything has a meaning, these phenomena presage the kind of weather which is to rule the autumn. Scarcely a summer bird remains save the swallow and martin. The swift left early. A solitary bird or a pair was observed, however, evening by evening up to the 28th to return to the nesting place of the tribe, as loth to leave the English home. To day (Friday) continuous rain, which has prevailed all the night. Mid-day, thermometer X. 64; barometer 29'3; set of wind southerly. Worcester, September 1

Habits of Spiders

YOUR Correspondent, Mr. Frank Rowbotham, in his letter on the "Habits of Spiders" (vol. xxvi. p. 386), gives it as his opinion that a spider shakes the web from a desire "to effect concealment when it feels danger is near." I am inclined to think it does so from a feeling of anger. During a long resi dence in the tropics, I often amused myself irritating spiders and watching their conduct. I noticed that they generally seized the web and shook it up and down in the manner described by your correspondent, but some of the spiders were of so great a size as to render concealment by such a manoeuvre quite hopeless, and I attributed their behaviour to other motives. They appeared to me more to resemble angry monkeys than anything else. I have not unfrequently seen the latter when annoyed jumping up and down on all fours with their tails erect in the air, or if confined in a cage seize the bars bp their hands and feet and shake W. J. C.

them as the spiders did their webs. Torquay, August 30

THE RESPIRATORY MOVEMENTS OF

INSECTS

THE HE respiratory movements of some of the larger insects are quite apparent, and have been described by various observers. A German naturalist, Herr Rathke, published in 1861 a memoir in which he compared those movements, observed with the naked eye and a magnifying glass, in insects of all the principal types.

According to M. Plateau (who has lately studied the subject, and has made a preliminary communication of his results to the Belgian Academy), though Rathke's memoir is very remarkable, he overlooked many details, and fell into sundry errors, owing to the difficulty of the inquiry.

Haussmann (1803) suggested a method of indicating the movements of dilatation and contraction of an insect's abdomen, by oscillations of a liquid column; but he recognised that it would apply only to articulata of large size, and it seems incapable of yielding very exact results.

M. Girard (1873) proposed encasing the insect's abdomen with a thin envelope of caoutchouc having a style attached which would inscribe the movements.

It is a form of the graphic method that M. Plateau first adopted. He confined himself to perfect insects, and directed his attention to (1) the form of the inspiration and expiration; (2) the parts of the body participating in the respiratory movements; (3) the expiratory and inspiratory muscles; (4) the influence of certain parts of the nervous system on the movements of respiration. The technical processes concerning the muscles and nervous

system are a matter of mere dissection, once the form of respiratory movement is ascertained, and the latter, therefore, chiefly claims notice in a simple résumé.

M. Plateau used two kinds of styles to inscribe the movements on a rotating blackened cylinder. One was a narrow light strip of Bristol paste-board, fastened to the part of the body whose movement was to be ascertained, with a little Canada balsam; the other a lever of the third order, turning freely about a horizontal axis placed at one end, and resting by its own weight, at a point near the axis, on the body of the insect (the insect, in either case, being supported fixedly in any desired position).

The graphic method is, however, unsatisfactory, and sometimes quite inapplicable, and M. Plateau used another along with it, viz. the method by projection, which gave excellent results.

The insect, fixed on a small support, so that the movements in breathing are not interfered with, is introduced into a large magic lantern lit with a good petroleum lamp. A reversed silhouette is obtained on the screen, and if a certain magnification be not exceeded (say 12 diameters), a very distinct image is produced, on which one may follow all the respiratory movements sufficiently amplified to indicate real displacements of a fraction of a millimetre. With a sheet of white paper over the image one draws the contours of the silhouette, corresponding to expiration and inspiration. Further, by changing the position of the insect, and by attaching short paper styles at parts whose movements are doubtful, a complete knowledge may be acquired of all details of the respiratory movements that characterise a given insect.

With a little practice, not only may the respiratory movements of small insects, such as flies, be easily studied thus, but a number of questions are unmistakably settled, which cannot be decided by direct observation.

The following is a brief résumé of the author's results :1. There is no close relation between the form of the

respiratory movements of an insect, and the insect's place in zoological classifications. The respiratory movements are similar only when the structure of the abdominal rings and the arrangement of muscles moving them are nearly the same. Among curious facts here, the movements of Phryganeidæ are unlike those of nearly related Neuroptera (such as Sialis), and like those of sting-bearing Hymenoptera.

2. In all insects the diameter of the abdomen diminishes in expiration by approximation of the dorsal and sternal arches of the segments; in some cases the dorsal, in others the sternal, showing the greater mobility; and in others both having nearly the same mobility.

3. The modifications in the vertical diameter may be accompanied by changes in the transversal diameter (e.g. Libellulæ).

4. Contrary to a former view, the changes of length of the abdomen, in normal respiration, by protrusion and return of the rings, are rare in insects; they are observed in an entire group only in the case of the sting-bearing Hymenoptera. Some isolated cases occur in the other zoological subdivisions (e.g. the caddis flies among the Neuroptera).

5. In the majority of cases, the thoracic segments do not participate in the respiratory movements of insects at rest. But the respiratory displacements of the posterior rings are less rare than Rathke supposed.

6. It has been thought that the respiratory movements in many insects were progressive, and propagated like a wave either from the base of the abdomen towards the point, or from the middle towards the two ends. This wave is, however, an exceptional phenomenon, is absent in all Coleoptera, in Acridians, in Libellulæ, in stingbearing Hymenoptera, in Muscides, and a part of Lepidoptera, and only appears in isolated forms in certain

groups.

7. When there is a pause in the respiratory phrases it always occurs in inspiration.

8. In all insects vigorous enough to furnish suitable curves (such as the large Coleoptera) one finds that the inspiration is usually slower than the expiration, and that the latter is often sudden (confirming an observation by Sorg in 1805).

9. In most insects expiration is alone active, inspiration being passive, and due to elasticity of the teguments and the tracheal walls. (This confirms previous observations.)

10. Nearly all insects possess only expiratory muscles. M. Plateau has found muscles aiding inspiration not only in Hymenoptera and Acridians (Rathke, Graber), but in Phryganeida.

11. The superior and inferior diaphragms of Hymenoptera have not the rôle Wolff attributes to them (a confirmation of objections by Graber).

12. Many insects, perhaps all, perform, with their abdomen, general movements, sometimes small, sometimes very ample, which do not coincide with respiratory movements, properly so called, and must be distinguished from them.

13. The respiratory movements of insects are purely reflex, persisting in the decapitated animal, and even in the isolated abdomen in forms whose nervous system is not condensed. In the latter case these movements are excited or retarded by the same causes which excite or retard them in the intact insect (a confirmation of previous observations).

14. The metathoracic ganglions are not, as Faivre supposed, special respiratory centres (a confirmation of the views of Barlow and Baudelot on Libellulæ).

15. The abolition of respiratory movements by destruction of the metathoracic ganglions in Dytiscidae and other Coleoptera, results from the condensed state of their nervous system, in which a certain number of abdominal ganglions are fused with those of the meta

thorax.

16. In insects with a condensed nervous system the excitation or partial destruction of a complex nervous mass resulting from the union of successive ganglionary centres always affects all the centres entering into the constitution of this mass.

DIARY OF VESUVIUS, JANUARY 1 TO
JULY 16, 1882

IN the account given in NATURE, vol. xxv. p. 294, the eruption that has been going on in December was described up to the last day of 1881. As the height of the lava column had been diminished by the lateral outlets, the surface was consequently some considerable distance below the lip of the crater, its level on ordinary occasions being only a few metres below.

Under ordinary conditions the ejectamenta consist of masses of fluid lava blown out as the spray from an effervescing liquid. They form the so-called lava cakes, being flattened out by their fall, while still plastic. They are usually very spongy, or scoriaceous, and rapidly disintegrate. In the present instance, however, as the vapours quitted the lava at some considerable depth, these plastic masses could not reach the surface. This rapid escape of vapour through the narrow tube between the lava surface and the crater lip, was under analogous conditions to the powder gas in a fire-arm. If, for instance, we imagine a cannon, whose bore is composed of materials easily broken up, we have a rough illustration of what takes place. The lava-cakes were replaced by ejectamenta derived from the components of the sides of the chimney, such as compact lava fragments, lapilli, old scoria cakes, all more or less altered and decomposed by the hot acid vapours, to which they had been exposed for considerable periods.

Such a condition of things naturally results in the straight-tube or chimney assuming the form of a funnel, or conical hollow whose apex will be at or near the lava level, that is to say, at the point where the gaseous products quit the fluid magma. We have, in fact, two conditions upon which the size and depth of a crater depend, namely, height of lava column, and amount and force of vapour escaping. Naturally the effect would be modified by local causes, and also the difference of com

Sketch after Nature on July 16, 1882, 9.30 a.m. View from the north of the cones and craters of December, 1881, and January to July 16, 1882. The outer rim is broken away over the old fissure to the left or east. The smaller bocca is beneath the little figure, there is probably the remnants of another beneath the middle, or left figure.

ponent materials. The ejectamenta which in this manner were very different from that of ordinary occasions, were deposited simultaneously in a rim-like manner around

the new crater.

Thus we see how a nearly perfect cone of eruption, such as existed in the beginning of December, composed as it was of alternate beds of lava and scoria cakes, with a chimney, but without a crater, may be converted into a low truncated cone, whose base is of an area considerably larger than that of the original, but whose height is much

N.

Α

1, Outline profile of apex of cone after eruption of 1872; 2, outline on December 31, 1881; 3, outline section on April 23, 1882 .e. the continuous line); 4, cone and crater formed between April 23 and July 16, 1882; A, materials, lava, and scoriæ since 1872; B, ditto, since December 31. 1881; c, ditto, since April 23, 1882.

less. The interior now occupied by a crater proportionally large. The whole of these changes occurring without the addition or abstraction of any materials, except an ash blown away by the wind.

On January 1, Vesuvius had become quiet, and the feeble ejections consequent thereon could no longer hoist the materials over the new crater edge, but were instead building up a new cone of eruption around the vent at the bottom of the craterial hollow.

Till January 14 no glimmer even was visible from Naples. On that evening, however, there was a slight red reflection, which continued till the 24th, when much vapour was escaping. The next day it became quiet. February 2, slight glimmer visible again.

From February 19 to April 23, the mountain remained very quiet; only the slightest glimmer visible at night. That day I visited the crater.

The crater and its rim of December and January occupies about one-third of the plain of lava filling the 1872 crater. The former overlaps the latter in a northeast direction, and is not therefore concentric. As we cautiously mount its northern edge to avoid the falling scoria cakes, it is seen that the craterial hollow has very steep sides, about 40 metres deep, and 150 metres in diameter. It showed the usual interlamination of lava and its fragmentary products. Rising from its floor was a small cone of eruption, that had been building up since the beginning of the year, its centre, of course, occupied by the vent, but no crater. The fissure mentioned in my last report was gradually filling up by the crumbling in of its sides; there was still oozing a small stream of lava from its lower extremity. This gentle flow of fluid rock had been going on without interruption since December, and during that period had been thrown out to a consider able amount, which, however, from slow exit soon cooled and had not enough impetus to travel far, chiefly piling itself up at the toe of the cone, and spreading a short distance over the Atrio and Valle dell' Inferno.

On May 13, became slightly more active, which continued till the 17th, the day of the eclipse of the sun. On that evening the reflection was very brilliant from a much increased flow of lava on the same side. From May 18 till June 6, gradually diminishing activity, especially during the last week. During the 4th and 5th, Prof. Palmieri recorded a continued uneasiness, as shown by the Vesuvian Observatory and University seismographs. That disturbance was the forerunner of a sharp earthquake shock, which occurred at 4'47 a.m. at Isernia and Vinchiaturo in the Appenines. At 8 a.m., when I scanned the crater with a glass, there seemed to be an increased volume of vapour from the fumaroles, and the main column was much more bulky and dense. In the evening the explosions reached a considerable height, and were very brilliant. On the 7th the same, but on the 8th quieter. We have here a small but good example of seismic energy exhibiting its focus of intensity in a mountain range, yet at the same time setting up sympathetic activity in the neighbouring volcano. In fact, I believe that if more accurate and regular observations were - carried on of earth tremors and the phases of volcanic activity, at many points scattered over such a country as Italy, much might be learned of the internal anatomy and physiology, so to speak, of such an area.

On July 16 I made a minute examination of the crater. Owing to a favourable wind, and with a muffle over the face, the edge of the innermost one could be reached. This, on which we were standing, was the cone of eruption that was commenced to be formed, in the bottom of the December crater, and whose growth had been going on up to June 29, when the increased activity of that and the following days, converted the top of the chimney into a small crater, at the same time scattering the materials on its outer flanks and increasing the size of the cone. The cavity, of an irregular conical form, was about 45 metres deep, and its apex could have been but little above the level of the outflow of lava that was still proceeding from the old lateral fissure. At the bottom of the crater was the bocca or mouth. Its position was slightly excentric, and irregular in form, being about 2×3 metres. It was apparently undercut by the lava that could be distinguished boiling up at a short distance from its edge, the issue of the ordinary column of vapours, carrying with each explosion a few fragments of the plastic mass, thus commencing a fourth cone within the inner crater. Part of the southern wall had crumbled away, showing well the stratification of the beds.

Between the inner cone of 1882 and that of 1881, that is to say, in the fosse-like excavation separating the two, and towards the south-west (below smallest figure in sketch), another bocca had opened. From 9 to 10 o'clock a.m., during which my examination had been carried on, only an abundant column of vapour had been emitted. When standing quite close to it, however, it suddenly started into increased activity, emitting a column of ash and lapilli, perpendicularly to some height, reminding one in form of the great geyser column of Iceland. This was due to the slipping of a part of the outer wall, which exhibited the stratification of the December cone. A continual play was maintained for about one hour and a half, when tranquility was restored. Mixed with the stones and lapilli that were being ejected were a few fragments of molten lava, demonstrating the opening to be in direct communication with the principal mass. Although one could approach the edge of the opening nothing could be seen, for the amount of vapour issuing. On that occasion the usual hydrochloric acid smell was strong but mixed with a little sulphurous, and I fancy I could detect a distinct odour of hydrofluoric acid, which is the first time. Of course it is known to exist in small quantities always.

The old lava forming the plain within the 1872 crater, and from which rise the two small cones above described, is much decomposed and covered by fumaroles, in a direction extending due south-west, that is to say, scattered along the same radius as the crateret above mentioned. It would seem from this to be the external evidence of a dyke which has extended in that direction. We might therefore infer that if any lateral opening should soon form it would be somewhere on the southwest of the cone. H. J. JOHNSTON-LAVIS

results.

The mountain from the last date to the 29th remained tranquil, no reflection being discernible at night. That evening, however, the ejections were to be seen distinctly. The following day it was the same, but on July 1 the activity had increased, and the lava that had now been arrested for weeks burst forth again at its old exit.

The mountain now took on somewhat an intermittent phase. On the third it was quieter, 4th the same, 5th, 6th, and 7th more active, 8th, 9th and 10th quieter, 11th and 12th more active, 13th, 14th, and 15th quiet.

THE HUNGARIAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE

BUDAPEST, August 28

ciation for the Advancement of Science has just been concluded. It was held at Debreczin a town of 52,000 inhabitants, and the capital of the great Hungarian Plain. Two hundred and eighty members were present, and of these 132 joined the Medical Section, while the remainder were divided pretty evenly between the Physi cal and Economic Sections. The Physical Section includes Chemistry, Mathematics, and Astronomy; and the Economic Section includes matters relating to Social Science and Agriculture. Unfortunately the Association

does not represent Hungarian science.

There is a

strong University party in Budapest opposed to its existence; and they give it no countenance either by their presence or otherwise. Nevertheless we are persuaded that the influence of the Association is good.

Debreczin is a great Calvinist centre. It has been called the "Rome of Calvinists." There is a Calvinist College which educates nearly 2,000 children, boys, and young men. Roughly there are 2,000 Calvinist parishes in Hungary, containing 2,000,000 souls, and of these 560 parishes and 800,000 souls are under the jurisdiction of the Bishop of Debreczin. The Bishop was President of the Association and the Sectional Meetings were held in the College. Great toleration exists in religious matters throughout Hungary, and the Calvinist Bishop and Roman Catholic Præpostor entered the Hall together and sat next to each other during the delivery of the Presidential Address.

On the evening of the first day of meeting, the train from Budapest which conveyed a number of members, was met at the station by the town authorities, and an address of welcome was delivered. We then went to the Town Hall, registered our names, received various publications including a fine volume giving a complete history from every point of view of the town, which has cost the municipal authorities 6000 florins. In the evening we all dined together. On the following day the Presidential Address was delivered at 10 a.m. This was followed by the reading of letters of salutation from various parts of Hungary. A paper was then read by Prof. Török one of the Vice Presidents on the Meteorites of Hungary, and specially on the Kaba meteorite which fell near Debreczin in 1857. This was the period of the Austrian domination. and many meteorites had already been taken from Hungarian museums and transferred to Vienna. A demand was at once made for the Kaba meteorite to be similarly transferred, but the Debreczin authorities answered, "It is true that you have a right to everything on and beneath the earth of Hungary, but this came from Heaven. Hence we propose to keep it here." And it remains in the Debreczin Museum. After the meteorite paper an eulogium was pronounced by Dr. Popper on Dr. Albert Kain, a recently deceased and prominent citizen. A short paper on children's diseases was then read by Prof. Bódogh, and the proceedings terminated at I p.m. Soon afterwards the members sat down to a public banquet of a very festive nature, which lasted till nearly 5 o'clock, and was notable for the national dishes, and profusion of native wines and mineral waters; of the latter Hungary possesses no less than eighty different varieties.

At 5 o'clock a lecture was given by Dr. Kiss on Hatvani, a professor of physics in the Debreczin College of the last century. He studied in Leyden and was the first to introduce experimental illustration into the college lectures. A good deal of his apparatus was exhibited and the air-pump with a huge horizontal barrel two feet in length and three inches in diameter, was particularly interesting. In principle it scarcely differed from Robert Boyle's second air-pump of the preceeding century.

At 9 a.m. on the following day the three sections were formed, and addresses delivered by the Presidents. The Physical Section was presided over by Prof Hunfalvi of Budapest, and his address was mainly devoted to the Meteorology of Hungary. He dwelt particularly on the great evils resulting from the cutting down of forests, and the climatal changes likely to result therefrom. As wood is commonly burnt for fuel in Hungary, and the winters are very severe, the destruction of forests is proceeding at a great rate. The address was considered of such importance that it was ordered to be printed separately and distributed all over Hungary. The Medical Section was presided over by Prof. Török, and the Economic Section by Prof. Kiraly. The meetings closed at noon, and recommenced again at 3 p.m. At 5 to a

very crowded audience Prof. Antolik gave a lecture on the electric discharge, with some original experiments. The Sectional Meetings were continued the next day and in the afternoon an excursion was made through the Debreczin Forest to an Agricultural College founded by the Government for the instruction of land agents and managers of large estates. The course extends over three years, and the students pay nearly £21 a year. The institution is a large model farm possessing a good deal of land, and very complete farm buildings in which fine breeds of cattle, horses, and pigs are reared. The bulls and horses are of particularly fine breed. In returning we halted at a forest hotel, dined, and afterwards danced, the national Csárdás being of course the most popular. Sectional meetings were continued during the following day, and on August 27 the closing meeting was held. In the afternoon there was an excursion to the salt lakes of Nyiregháza.

The invitations were written in Latin, as of course Hungarian is a language, not much known out of the country. They were worded as follows:

"Doctores Medicinæ et naturæ scrutatores Hungariæ, hoc anno Debrecini a 20-27 Mensis Augusti, Congregationem Scientificam sunt celebraturi.

"Cum ad hoc Congregationem D. . . . M. ... N. . . . solemniter invitaremus, simul impense, rogamus, ut nos gratissima sua præsentia honorare, vel aliis hunc honorem delegare, congregationisque medicorum et naturæ scrutatorum in cognoscendio rerum causis positum studium favore et si lubet opera prosequi non dedignetur.

"Dissertationes de naturâ rerum agentes, secundum statuta congregationis, quâcunque linguâ haberi possunt. "Sincerissimam quam possumus salutationem exhibentes perseveramus. Debrecini, 4 Mai, 1882."

A few years ago Latin was commonly spoken by educated Hungarians, and Latin words are now frequently used in intercourse with foreigners. One morning when I was looking for my host, his little son gravely gave me a letter which he had rapidly penned, expressed with the following charming naiveté:-"Domine Professor! Meus pater est in Collegio. Si Vestra Dominatio alloqui illum vult, voco statim domo. Hora nona certe redibit." And while on the subject of colloquial Latin in this country, we are fain to remember the story of the English sailor, who was rolling a gigantic piece of tobacco in his mouth, to whom a Hungarian, unused to the custom said, pointing to the distended cheek, "Quid est hoc?" whereupon the sailor answered readily, "Hoc est quid."

It is impossible to conclude this short notice of a very interesting scientific meeting, without mention of the extraordinary cordiality and hospitality of the town of Debreczin. G. F. RODWELL

THE

THE BRITISH ASSOCIATION HE number of papers in the two leading departments of the Biological Section were very few this year, as indeed they have been for some years, and therefore it was decided by the General Committee that the number of departments of that section be reduced from three to two. Next year's meeting was fixed for September 19, with the view of bringing it towards the close of the holidays rather than in the middle of them. A formal resolution was also passed authorising the Council to make the best arrangements they can for securing an equal representation of all the sections at the meeting proposed to be held at Montreal in the succeeding year. One or two speakers seemed to doubt whether the matter could be regarded as finally settled. A suggestion was made that a meeting should be held in this country as usual, and that the vice-presidents should go to Canada as delegates. It was stated on both sides that members were absent at Monday's meeting whose votes would have materially affected the decision arrived at. It is

matter of satisfaction that Southport contains numerous public meeting-places close to each other. The scattered position of the Sections at the present meeting has been a very serious obstacle to members wishing to hear papers in different Sections on the same day. This has been especially the case in Section C, which, being half a mile from most of the other Sections, seldom obtained a good audience, and indeed was only filled when the popular subject of the Channel Tunnel was brought before the Section by Messrs. Boyd Dawkins and De Rance.

REPORTS

Report of the Committee consisting of Prof. Roscoe, Mr. Lockyer, Prof. Dewar, Prof. Liveing, Prof. Schuster, Capt. Abney, and Dr. Marshall Watts, appointed at the York Meeting to prepare a New Series of Wave-lengths Tables of the Spectra of the Elements.-This Committee report that they have lately obtained an instrument for the more exact performance of the process of graphical interpolation, constructed by Messrs. Cooke and Sons of York. And since this instrument has only been received within the last few weeks they are not in a position to make a detailed report to the Association.

The Report of the Committee consisting of Prof. Balfour Stewart, Thorpe, and Rücker, appointed at the York Meeting to Report on Methods of Calibrating Mercurial Thermometers was read by Prof. Rücker. Thermometer tubes are in general of unequal bore in different parts, and the indications of the instru ments will thus be erroneous, unless these irregularities are al owed for. If a short column of mercury broken off from the main mass in the bulb and tube be measured in different parts of the tube, its length will be greater in the narrower, and less in the wider parts. By means of such measurements the correction for the inequalities in the bore can be applied in two different ways distinguished as methods of calibration and correction respectively. In the first the length of the column of mercury i, ineasured in various parts of the tube before the scale is etched on it, and the lengths of the divisions are then so adjusted as to make equal differences of scale readings correspond to equal

volumes. In the second the tube is in the first instance furnished with a uniform scale, and a table of corrections is afterwards drawn up, by means of which the same end is attained as before. In either case the measure nents have to be made in some syste.natic manner, and a number of different methods of performing the ob ervations and calculations have from time to time been proposed. That in use at the Kew Observatory is the simplest of all, while the more elaborate methods have for the most part been proposed by German writers. The report conited of a minute discussion of the relative merits of these various methods, the chief of which had been applied by the Committee to the same thermometer, so that the results could be readily compared. The measurements for this purpose were made in the Physical Laboratory of the Yorkshire College. The methods chiefly investigated were Gay Lussac's, Hällström's, Thiessen's, Marek's, Rudberg's, and Bessel's, both as modified by von Oettingen, and also with further modifications introduced by Professors Thorpe and Rücker. As the result of a long theoretical and experimental investigation, the Committee conclude that labour is saved and equal accuracy secured by the repetition of the simplest method of correction (Gay Lussac's), instead of the employment of more elaborate and theoretically more perfect schemes.

Report of the Committee, consisting of Professors Odling, Huntington, and Hartley, appointed for the Purpose of investigating, by means of Photography, the Ultra-Violet SparkSpectra emitted by Metallic Elements and their Combinations under Varying Conditions.-This report was drawn up by Prof. Hartley, and communicated to the Section by Prof. Huntington. The object of this investigation was to give, first, a means of readily identifying the metals by photographs of their line spectra; secondly, a knowledge of the alterations producible in the spectra of metallic salts by the presence of various nonmetallic elements; thirdly, a knowledge of the alterations caused by the dilution of metallic solutions; fourthly, a possible means of performing rapid quantitative determination of metallic substances by the aid of photography, and obtaining permanent records of the results. These objects have been more or less

solution of the pac ical difficulty of obtaining photographs of spark spectra of metallic salts from their solutions; (2) the comparison of spectra yielded by metallic electrodes with those obtained from saline solutions; (3) the variations in the spectra caused by dilution of saline solutions; (4) the sensitiveness of spectrum reactions under certain conditions; (5) the variation in the spectra of metals caused by alterations in the inten-ity of the spark employed. A comparison of the spectra of solution of salts with those of metallic electrodes show that in almost all cases the lines of the metals were produced from the solutions. The non-metallic constituents of salts do not yield any marked series of lines. The spectrum of aluminium, as obtained from pure solutions, is free from a group of short or discontinuous lines, which the author has shown to be due to iron. In estimating the relative proportions of the constituents of alloys or ininerals, only those methods are to be recommended in which solutions are used, as in this way the non-homogeneity of the substance under investigation can alone be obviated. With regard to the reversal of metallic lines, it is pointed out that over-expo-ure suffices to produce reversal without materially influencing the rest of the spectrum; and in order to obviate this result, it is recommended that comparative exposures should be methodically employed to confirm the accuracy of observations made entirely by the aid of photographic representations and of spectra. This is especially the case where gelatine or other dry plates containing organic matter are employed.

Report of the Committee on the Lunar Disturbance of Gravity, by G. H. Darwin.-Shortly after the reading of the first report last year at York, it was found that the instrument with which he and his brother had been working, had broken down, and this together with a series of unforseen circumstances, had prevented their continuing their observations. But he still had some remarks to make on the subject. From a remark made by Signor de Rossi on an observed connection between barometric storms and the disturbance of the vertical, he had been led to make some investigations on the mechanical effects caused by variations of pressure acting on an elastic surface. When a heavy body rests on the surface of the earth in the neighbourhood of a pendulum, the direction of the pendulum, or the vertical, appears to change, a change due to two causes: first, an actual change due to the attraction of the heavy body on the bob of the pendulum; and secondly, an apparent change due to surface. Sir W. Thomson had pointed out to him a very rean actual change of level caused by the elastic yielding of the markable relation between those two effects. If a heavy mas of any form be placed on the surface of an elastic plate of great thickness, the deflectin produced on a plumb-line suspended over any point of the plate by the attraction of the mass is proportional to the slope produced in the plate at the same point by the elastic yielding to the mass. Applying this to the case of variation of barometric pressure, and supposing the earth to have a rigidity between that of glass and copper, he found that the varia tion of slope between two places 1500 miles apart due to a difference of 5 cm. of barometric height would be o"0117, whilst if the attraction of the air be included, it would amount to 0 0146. Thus, considering two cases of high pressure to right and left, there would be a difference in the position of the plumb-line relatively to the earth's surface of o0292. The amplitude of oscillation at Cambridge due to lunar dis urbance of gravity, year's report shown to be o" 0216, whilst the instrument was as computed on the hypothesis that the earth i, rigid, was in last capable of detecting changes of o"01. As these quantities were all of the same order of magnitude, he came to the conclusion that it was hopeless to expect determinations of the lunar effect by experiment based on the pendulum method. There was another effect due to change of barometric pressure, viz an Under the same circum

alteration in the altitude of the surface.

be 9 cms.

Near a coast line the

metre from the water's edge would be 0076.-Sir W. Thomson pointed out a method by which the effect of the attraction of the