of the Bombay Presidency, and that the proportionate increase or decrease of the abnormal rainfall, corresponding to a fall or rise in the abnormal pressure of a tenth of an inch of mercury, amounts to more than one hundred per cent. of the normall fall; but that the variations of the ordinary monsoon gradients produce very different effects on the rainfall of different districts, depending on the geographical peculiarities of the particular locality.

From all these facts it is clear that there is some intimate relation between the variations of sun-spots, barometric pressure, and rainfall; and as famines in general are induced by a deficiency of rain, it is probable that they also may be added to the above list of connected phenomena. What is required in order to gain an insight into the causal relation of these variations is

that they should each and all be studied in greater detail than has hitherto been attempted. Accordingly I commenced, more than a year ago, a detailed investigation into the nature of the abnormal variations of barometric pressure, and have been led to the discovery of some new facts which appear to me to be of sufficient importance to render it desirable that they should be published in anticipation of the theoretical conclusions deducible therefrom.

Commencing with the daily abnormal barometric variations observed at several stations in Western India, it was soon found that as the time over which an abnormal barometric fluctuation extended became longer and longer, the range of the fluctuation became more and more uniform at the various stations, thus leading to the conclusion that the abnormal variations of long

duration affect a very wide area. To test this inference it became, necessary to compare the observations recorded at Bombay with those of some distant tropical station. Batavia was chosen, and on curving the daily observations side by side with those of Bombay, the degree of accordance between them was found to be truly surprising, considering how far the two stations are apart. The next step was to compare the monthly abnormal variations of these two stations, and finding that they presented many similar features, as well as some differences, to smooth the variations by taking three-monthly means. The degree of accordance was now found to be still greater, many of the discordances having been eliminated in the process of smoothing; but as some differences were still observable the process was repeated, giving nine-monthly means of abnormal pressure corre

sponding to the middle of the months January, April, July, and October of each year. The curves obtained in this way for Bombay and Batavia were then found to be almost identical in form, but with this very remarkable difference: the curve for Batavia was seen to lag very persistently about one month behind the Bombay curve. Similar results were then worked out from all the available data for the following tropical stations: St. Helena, Mauritius, Madras, Calcutta, and Zi-ka-wei, and for comparison with them the monthly sun-spot areas 1 were treated in exactly the same manner. The results are given in the fol lowing table, and graphically represented by the continuous curves on the annexed plate :

Taken from the paper by Messrs. De La Rue, Stewart, and Loewy, published in the Philosophical Transactions for 1870, p. 122.

Comparison of Abnormal Barometric Movements at Different Stations.-The general resemblance of all these curves to each other is very remarkable; indeed if the Mauritius curve for the years 1867 and 1868 be excluded, there is scarcely a single prominent feature in any one of the curves which is not reproduced in the others. To show this the corresponding points of the different curves have been marked with the same small letters. It will be seen, however, that there is strong evidence of a want of exact simultaneity in the barometric movements at different stations, and that as a rule the changes take place at the more westerly stations several months earlier than at the more easterly ones. This is particularly noticeable in the curves for St. Helena and Madras from 1841 to 1846, when the latter sometimes lagged behind the former by as much as six months; in those for Mauritius and Calcutta from 1855 to 1866, when the latter persistently lagged several months behind the former; in those for Bombay and Calcutta from 1862 to 1866, when the difference in time often amounted to upwards of six months; in those for Bombay and Batavia from 1867 to 1878, when (as already remarked) the latter lagged behind the former at an average interval of about one month; and in those for Bombay and Ti-ka-wei from 1876 to 1878, when the latter lagged upwards of six months behind the former. It appears then that these long atmospheric waves (if such they may be called) travel at a very slow and variable rate round the earth from west to east, like the cyclones of the extra tropical latitudes. Bombay FRED. CHAMBERS

(To be continued.)

DR. SIEMENS'S NEW CURE FOR SMOKE

FROM among a number of letters which have been sent us on

this subject we have selected the following for publication; to these Dr. Siemens has been good enough to append some important remarks.

IN NATURE, vol. xxiii. p. 25, I read with interest an article by Dr. Siemens describing an ingenious gas and coke fire which he suggests as a cure for the smoke nuisance. But although the darkening of the atmosphere or fog will certainly be prevented by its use, I am afraid the gases from the coke, especially the carbonic oxide, will make the fogs at least as poisonous and injurious to health as the open coal fires at present in use.

In these circumstances a description of an 66 Asbestos gas fire" free from this objection, which we have had in use in our smoking room for the last three years, and which, after a few alterations, has proved perfectly satisfactory, may perhaps interest your readers.

A-inch gas-pipe furnished with four Bunsen burners is laid on the hearthstone under the grate and parallel to the ribs, so arranged that the tops of the burners (which are made elliptical to pass through the bars) are flush with the upper surface of the grate, and two inches back from the line of the ribs. The fireplace is loosely filled with a preparation of asbestos in pieces about the size of a hen's egg.

This fire not only evolves a large amount of heat, but has a very cheerful appearance, similar to that of a bright coke fire, and to insure this it is essential that the burners should be placed close to the ribs, as stated above, and not in the centre of the grate. If this is not attended to the asbestos in the centre of the fire will be raised to a high temperature, but will not be sufficient to heat those portions in front, which will then not only be of no use as radiators in themselves, but act as screens to the light and heat generated in the centre. I suspect this was the cause of the failure of Dr. Siemens' pumice gas fire.

The cost of maintaining this fire is simply that of the amount of gas burned, as the asbestos is not consumed, and its prime cost is trifling. I have only further to add that there is not the slightest trace of fumes or smell from the fire two minutes after it is lighted. D. A. STEVENSON

Edinburgh, November 15

DR. SIEMENS has described in your pages the form of cokegas grate which he has fitted in his own house. As I had fitted a similar arrangement in this house before Dr. Siemens' letter appeared in the Times of November 3, and as it is simpler than Dr. Siemens' and succeeds even beyond my expectation, I send you a drawing and description of it. It varies, of course, according to the shape of the grate in which it is fitted; but for the sake of comparison I have copied Dr. Siemens' grate, and drawn my arrangement as fitted into it.

Instead of Dr. Siemens' arrangement for withdrawing the heat from the back of the fire and bringing it to the front, I merely line the whole grate-sides, back, and bottom-with fire-bricks. This obviates the necessity for the close-fitting ash-pan described by Dr. Siemens, which would be rather expensive to fit. I make the fire-brick in the bottom of the grate slope towards the front, and leave a space of one inch between the front of it and the perforated gaspipe down which space the ashes fall on to the hearth.

If my grate is not quite so economical in working as Dr. Siemens', it is very near it, and the first cost of fitting is consi derably less. In fact, as most grates are lined with fire-brick at back and sides, nothing has to be done but fit a wedge-shaped fire-brick into the bottom, a half-inch iron gaspipe, perforated with holes in front, and connect it with the gas service, all of which can generally be done for a few shillings.

The saving of kindling-wood and of chimney-sweeping would pay for it in a year. In Dr. Siemens' grate the copper must cost about 1. A grate fitted with this arrangement looks exactly the same as an ordinary grate, and there is nothing to prevent ordinary coal being burnt in it-in fact coal can be burnt in it with much less smoke than in an ordinary grate by turning on the gas for a few minutes when fresh coal is put on, when the dense black smoke emitted by the new coal is completely burnt up in the gas-flame. To people who object that a gas grate must produce a bad smell in the room I can only say, "Come and see." They will find that we have three grates with this arrangement in constant use in these chambers, and that they produce no smell and make a very pleasant fire. Any person who takes an interest in the subject is quite welcome to come in and look at them at any time. COSMO INNES

Adelphi Chambers, 7, John Street, Adelphi

HAVING been experimenting for some years in the direction referred to by Dr. Siemens in NATURE, vol. xxiii. p. 25, I must beg to differ with him most seriously in some of his conclusions. The gas-fire with coke which he describes has, so far as our experience goes, several practical objections which prevent its use in the place of an ordinary gas fire, whilst when compared with a good coal fire it fails seriously.

First, with regard to the objections to Dr. Siemens' fire. It requires about half an hour to become anything like warm, as against ten to fifteen minutes with a well-lighted coal fire. Second, it makes as much or more dust and dirt than a good coal fire. Third, the grate requires as much cleaning and care as with coal.

I am not surprised at the economy, comparing the coal fire as shown with gas and coke, but if the result had been taken in

comparison with a good Abbotsford grate with solid clay bottom, back and sides, the figures would have appeared seriously the other way.

In a room of exactly half the cubic area of the one referred to by Dr. Siemens we have an Abbotsford grate a little over 3rd cubic foot capacity, the actual measurement of the fire space being 5 inches deep, 8 inches back to front, 14 inches wide. This is lighted at 7 o'clock every morning and at 10 o'clock the grate is filled (not piled high). This fire burns until 10 or 11 o'clock every night untouched, practically smokeless, making the room pleasantly warm all over in the severest weather, and without making a handful of cinders in a month. One ordinary boxful of coals lasts two days. We have five, sometimes six, fires going daily at an average cost for coal for the winter season of five shillings weekly, or less than twopence per day per fire. That Dr. Siemens is correct so far as the old style of fire-grate is concerned, I know to my cost, but taking any good grate with clay sides and back and a solid clay bottom, his fire at its best will not compare either for cleanliness, economy, or comfort.

Gas fires are wanted where absolutely no attention and dust can be permitted. Allowing either of these as possible, no substitute I know will approach a well-constructed open fire with a solid clay bottom and fire-box.

With regard to the waste heat, it is no greater than absolutely necessary to take away the products of combustion, as, with our grates, it is utilised for warming the upper rooms. At this moment, with five good fires, there is visible from the tops of our chimneys nothing except a clear transparent current of warm air; any one at a cursory glance would say there were no fires in the house.

It must be borne in mind when I refer to cost that we cook entirely by gas, and the price of good coal here is 14s. 2d. per ton, coke being about half this price. What is required in a gas fire is a perfectly clean source of radiant heat, without trouble, and quickly available: these conditions are not in any way fulfilled by Dr. Siemens' arrangement. With the exception of two or three minutes expended in lighting, all he has attained can be found in a more perfect form in many of the fire-grates which have been in common use for the last ten years. Amongst our many attempts at gas fires one, although not absolutely the same as Dr. Siemens', was practically so, and was condemned because it required as much trouble as our present fires, and was much slower in lighting. It would be both interesting and instructive if Dr. Siemens would test an Abbotsford grate under the same conditions as his coke gas fire, and supplement his report with one from the individual who has to do the cleaning up and dusting, a department which it is more than probable he ignores. Another important matter is that I believe the cost of making and fixing Dr. Siemens' grate would be not less than that of a good modern fire-grate. THOS. FLETCHER

Warrington

THROUGH your courtesy I am enabled to reply to the objections raised by three correspondents against my proposed gis-coke grate, before they have actually appeared in your columns.

Mr. D. A. Stevenson considers that the use of coke is objectionable on account of the gases evolved in its combustion, and especially the carbonic oxide gas, which would poison the atmosphere. In reply I have to say that in burning coke with a supply of hot air, and in contact in front of the grate with the atmosphere, its entire combustion is insured, resulting in carbonic acid, which is a necessary constituent of our atmosphere. In obtaining the same amount of heat through the perfect combustion of gas, products of combustion at least equally objectionable from a sanitary point of view will be evolved.

The gas-asbestos grate which he describes appears to be judiciously contrived, but its power of heating the room depends entirely upon the combustion of gas unaided by hot air or solid fuel. Now 1000 cubic feet of gas weigh about 34 lbs., and the heat developed in the combustion cannot exceed 34 X 22,000 = 748,000 units of heat.

The heat units produced in burning a pound of coke may be taken at 13,400 (assuming it to contain about 8 per cent. of incombustible admixture, the heat equivalent of pure carbon being 14,500 units), and it requires 748,000 = 56 lbs., or just 13,400 half a hundredweight of this coke, to produce the heating effect of 1000 cubic feet of gas.

=

Taking gas coke at 18s. per ton (which is an excessive price), the 56 lbs. of coke represent a cost of 5'4d., as compared with 35. 6d. for the 1000 cubic feet of gas producing the same amount

of heat. This great difference of cost at once shows the advantage of making coke do as much of the work as possible. Without it a gas grate will consume 50 to 70 cubic feet of gas per hour, whereas my experiments prove that an average consumption of 8 cubic feet suffices to heat a large room when combined with a moderate consumption of coke, and with the use of the heating arrangement, to which I attach great importance. Another important consideration in favour of the joint use of coke and gas is that the existing gas companies produce both these constituents very much in the proportion in which they would be required, and could therefore provide the means of supplying an enormous number of coke-gas grates, whereas their plant and mains would be quite inadequate to supply a demand upon them for an extended application of purely gas stoves.

Mr. Cosmo Innes describes a gas grate of his construction, having the closed grate and single gas pipe behind the lower front bar which I advocate; he proposes to fill the grate with common coal, using the gas only as a means of kindling the fire. My objections to his proposal are that in using coal he must continue to make smoke, which we are desirous to prevent, and that the hot back to his fire means rapid distillation of the fuel up the chimney in the form of hydrocarbons and carbonic oxide. The gas arrangement as shown by him will be efficacious, no doubt, as a means of kindling a bright and cheerful fire, but he

b

would do better in that case to use a few logs of wood instead of coals. A bright but short-lived fire may thus be raised quickly at a cheap rate in a dining-room or in a parlour.

Mr. Thomas Fletcher admits that my grate has the advantage of economy over a common coal grate, but thinks the Abbotsford grate the best of all. This grate is according to him practically smokeless, and produces only a handful of cinders in a month, detract from the merits of the Abbotsford grate, but I fail to see although common coal is used. Now I have no desire to why it should be smokeless, considering that raw coal is used; imply that Mr. Fletcher uses an extremely pure and probably a and the extremely small production of ashes or cinder seems to smokeless coal, very different from the fuel we are usually supplied with in London.

He also objects to the cost of my arrangement, and his opinion in this respect, coming from a practical grate-builder, is entitled to every consideration. In first describing my plan I did not go into the question of cost of application; but having been since asked by grate-builders to advise them regarding the cheapest form of my grate and the easiest mode of applying it to existing fire-places, I have devised a form of application which leaves little to be desired, I think, as regards first cost.

The arrangement is shown by the accompanying sketch, and consists of two parts which are simply added to the existing

grate, viz. :-(1) the gas-pipe (d) with holes of about inch diameter, 15 inch apart along the upper side inclining inward, and (2) an angular plate (a) of either cast or wrought iron, with projecting ribs (6) extending from front to back on its underside, either cast with or riveted to the same, presenting a considerable area, and serving the double purpose of supporting the additional part on the existing grate, and of providing the heating-surface produced by the copper plate and frill-work in my first arrangement. In using iron instead of copper it is necessary however to increase the thickness of these plates and ribs in the inverse ratio of the conductivity of the two metals, or as regards the back plate, from inch to inch.

The arrangement will be rendered more perfect by the use of the bent plate fastened to the lower grate bar, which directs the incoming air upon the heating-surfaces.

The front edge of the horizontal plate has vandyked openings (c), so as to form a narrow grating, through which the small quan

tity of ashes that will be produced by combustion of the coke and anthracite in the front part of the grate discharge themselves down the incline towards the back of the hearth, where an open ash-pan may be placed for their reception.

In adapting the arrangement to new grates, the horizontal grating had better be dispensed with, and the casting with its lower ribs extended downwards, so as to find its fixed support between the back of the fireplace and the inclined deflector plate. Mr. Fletcher speaks of the large amount of ashes that would be produced, but this amount can surely not be as great as in the case of a coal fire, seeing that the consumption of solid fuel is reduced to less than one-half, of which nearly one-half is anthracite, a fuel remarkably free from ashes. Neither do I participate in Mr. Fletcher's fear regarding opposition on the part of housemaids, except it be from an apprehension on their part that, with Othello's and the chimney-sweeps', their "occupation be gone."

The tendency of grate-builders of the present day, and also of

your correspondents, appears to be to look for economy to bricklinings, which no doubt have the effect of producing hot radiating surfaces. I maintain however that such radiation is obtained at too great a cost of fuel, and that superior economical results will, on the contrary, be attained by abstracting the heat from the back of the fire, and concentrating it upon the purely carbonaceous material in front of the same.

To illustrate my reasoning I may here refer to an experiment which can easily be made of throwing a shovelful of bituminous coal into a steel-melting furnace; the result is an instantaneous dispersion of the coal, accompanied with a powerful refrigerative action on the furnace. In constructing gas-producers I take advantage of hot walls to turn solid into gaseous fuel, and a fireplace with hot brick bottom and sides is very much in the condition of a good gas-producer, giving out radiant heat no doubt, but combined with rapid distillation of combustible gases into the chimney. This action is made apparent in placing on the fuel towards the back of such a grate when in full glow a piece of wood, which will be seen to dwindle away rapidly without giving rise to flame, the atmosphere immediately over the glowing fuel being essentially a reducing one.

In my grate the heat, on the contrary, is confined to the coke immediately behind the bars, in contact with the heating gas flames and with the air of the room flowing in towards the chimney, whereas the coke at the back of the grate remains comparatively cool and unconsumed throughout the day. The cold furnace-back also means a cold chimney, and it is rather remarkable to observe that in the case of the application at my office, a thermometer held high up into the chimney showed a temperature of only 130° F., while the front of the grate was in a high state of incandescence. These, I maintain, are conditions most favourable to economy combined with entire absence of smoke or deleterious gases. C. WILLIAM SIEMENS

12, Queen Anne's Gate, S. W., November 24

CURIOUS IMPRESSIONS IN CAMBRIAN SANDSTONE NEAR LOCH MAREE

IN course of the short excursion to Loch Maree and its neighbourhood, Mr. Walter Carruthers, of the Inverness Courier, happened, on June 13, to light upon an interesting portion of the Cambrian or Torridon Red Sandstone of the district, forming part of the bed of the burn, near Loch Maree Hotel, on which occur what have been called the Victoria Falls, so named from the fact that the Queen visited them. There an exposed surface of the rock about sixteen feet in length, nearly as much in breadth, and almost perfectly level, is marked by several double grooves quite discernible, and each divided by a very thin raised line. These traverse the whole length of the rock in a perfectly straight line, and on both sides of them are roughnesses which, if we could entertain the idea that the grooving had been caused by some living creatures, might be produced by footprints which have been to a great extent obliterated. The impressions were so striking that they immediately suggested a recollection of the footprints discovered in the sandstones of Morayshire and Tarbatness, though there was no other resemblance than their marked character on the broad, flat rock. Having heard that Mr. William Jolly, H.M. Inspector of Schools, was in the neighbourhood, Mr. Carruthers called his attention to the subject, and indicated where he should find the markings. Mr. Jolly was not slow to examine the spot, and he writes to Mr. Carruthers as follows, as given in the Inverness Courier of July 1 :

"I found your curious lines without difficulty, guided by your accurate description of their locality. They are assuredly no 'mare's nest,' but bonâ fide ancient impressions of some kind, which should receive the attention of geologists, both on their own account and as existing in the second oldest geological formation in Britain, in which, as yet in Scotland, no evidences whatever of organic life have been discovered.

"The lines or bands in question occur in the chocolatecoloured Torridon sandstone, the Cambrian of Murchison and Geikie, which is so well developed around Loch Maree, and rises into the great dome of the Slioch, or the Spear Head, that guards its waters. The most distinct of the impressions consists of two continuous flat bands side by side, 1 to 1 inch broad, and about a quarter of an inch deep, running quite straight across the flat layers of sandstone in situ, and perfectly distinct for sixteen feet, disappearing on the west side under the superincumbent rock, and broken only where portions of the sandstone have