Even if this were the time and place, I should not venture to submit Sir Benjamin Brodie's views to that exhaustive analysis, which I believe has hitherto never been accorded to them, but which they must ere long receive at the hands of chemists. As yet only portions of the Calculus have been published, viz., Part I. "On the Construction of Chemical Symbols," and Part II. "On the Analysis of Chemical Events," although a valuable supplementary explanation of certain features was recently elicited by Naquet's criticisms. We have still to learn how the author proposed to treat of isomerism, by far the most intricate and difficult problem yet to be solved in chemistry, and let us hope that his departure from amongst us, which we now deeply lament, may not involve the suspension of judgment on this point he asked for but a short time ago being for ever.

I cannot refrain from devoting this notice to specially directing attention to what appears to me to be the topic of fundamental importance in the lecture, viz. the suggestion, made the author believes for the first time excepting in a few words at the conclusion of his first Memoir in the Philosophical Transactions, of the possible decomposition at the elevated temperature of the sun of certain

chemical elements.

The fundamental hypothesis of the Calculus is to express the symbol of the unit of hydrogen by one letter, a. Hydrogen is to be regarded as constructed at once, by one operation. But while hydrogen is conceived of as the product of a single operation, the hypothesis indicates that oxygen, έ, cannot be conceived of as made by less than two operations; while chlorine, ax, and nitrogen, a2, for example, are each to be conceived of as made by three operations, one operation in each case being that by which hydrogen is made. In short, the hypothesis involves the conclusion that there are several distinct classes—three at least-of "elements," of which hydrogen, oxygen and chlorine are the types, formed respectively by a single operation, by two similar operations, and by several operations not all similar. In other words, to quote the author, we are led to a certain physical hypothesis as to the origin and causes of chemical phenomena."

66

He then continues :—

"Now what I am going to suggest you must consider to be put before you with reservation, but we may conceive that in remote time, or in remote space, there did exist formerly, or do exist now, certain simpler forms of matter than we find on the surface of our globe-a, x, έ, v, and so on-I say we may at least conceive of, or imagine, VOL. XXIII.-No. 581

the existence in time and space of these simpler forms of being, of which we have some records remaining to us in such elements as hydrogen and mercury. We may consider that in remote ages the temperature of matter was much higher than it is now, and that these other things existed then in the state of perfect gases-separable existences-uncombined. This is the farthest barrier to which in the way of analysis theory can reach. Beyond all is conjecture. There may be something further, but if so, we have no suspicion of it from the facts of the science. We may then conceive that the temperature began to fall and these things to combine with one another and to enter into new forms of existence, appropriate to the circumstances in which they were placed. We may suppose that at this time water (a §), hydrochloric acid (ax), and many other bodies began to exist. We may further consider that as the temperature went on falling, certain forms of matter became more permanent and more stable, to the exclusion of other forms. We have evidence on the surface of our globe of the permanence of certain forms of matter to the exclusion of others. We may conceive of this process of the lowering of temperature going on so that these substances, a x2 and av, when once formed, could never be decomposed-in fact, that the resolution of these bodies into their component elements could never occur again. You would then have something of our present system of things."

We have here a most distinct prior statement by Sir Benjamin Brodie of views almost identical with those which have been so persistently urged for several years past by Mr. Lockyer, whose arguments, however, have hitherto met with but little sympathy from chemists, mainly perhaps on account of the unwonted character of the evidence. In his paper read before the Royal Society in December 1878, Mr. Lockyer adduced two lines of evidence in support of his hypothesis of elemental dissociation at high temperatures: The existence of lines common to several spectra-socalled basic lines-and the progressive alteration in the character of the spectra of the stars with temperature. Neither of these lines of argument has, I believe, yet been impugned, and the criticisms launched against the hypothesis have been on side issues of no real importance to the main question under discussion. More recently additional evidence in the same direction has been obtained by the comparison of the observations of Tacchini and others on solar storms. It appears that whereas at certain times lines which are admittedly all iron lines are visible, at other times certain of these lines. are wanting from the spectrum, new lines appearing in their place: fluctuations of this kind taking place at frequent intervals, but evidently in accordance with some well-defined law. Facts such as these may after all meet with some other interpretation than that furnished by the "dissociation" hypothesis, although at present this affords by far the simplest explanation of them. A communication of Mr. Lockyer's, read at the last meeting but one of the Royal Society, however, adduces evidence which if confirmed must, it would seem, be regarded as final. It is well known that the velocity of uprush or downrush of vapours at the sun may be determined by observations of the amount of displacement from their normal position of the lines in the spectrum of the vapours, and obviously if all the lines in a given spectrum-that of iron, for instance-are lines due to one substance, it must be a matter of indifference by which of the lines the velocity is measured. Whereas, on the other hand, if this be not the case, and the simpler substances into which the body

H

is split up be of different degrees of volatility-of different molecular weight-we may expect that measurements of the displacement of different lines will not all furnish the same results. Mr. Lockyer states that in an observation of a sun-spot on August 31 of this year, when the iron line at 5207'6 was doubly contorted, indicating an ascending and descending velocity of about fifteen miles a second, the two adjacent iron lines at λ 52037 and 52016, visible in the same field of view, were perfectly steady. Observations of this kind are necessarily very difficult, and the communication is made with all reserve; but it is to be hoped that observers elsewhere will co-operate in at once putting this observation to the test.

It is difficult to exaggerate the importance of the question to the chemistry of the future, for should it once be proved that the dissociation of the so-called elements is taking place in the sun and still hotter stars, it will be within the power of the physicist with the aid of the telespectroscope to build up a theory of elemental evolution not inferior in interest to the doctrine of organic evolution. For my part, I have no fear of the result, for apart from Sir Benjamin Brodie's hypothesis and apart from spectroscopic evidence, I believe that in the relations of the "clements" to each other when arranged more

Whatever the nature of the dissociation products, the occurrence of dissociation must be regarded as placed beyond doubt, for Victor Meyer's results have been in the main confirmed not only by Meier and Crafts, but also by Deville and Troost, who had previously obtained normal results. Bromine does not undergo dissociation so readily as iodine, the ratio of the observed to the theoretical "normal" density being, according to Meier and Crafts, 8 for bromine when it is 66 for iodine. In a recent communication, Victor Meyer has stated that the results of his earlier experiments with chlorine would appear to have been vitiated by some as yet undiscovered source of error; this gas probably is not dissociated except at extremely high temperatures, and it is doubtful whether there is any difference in behaviour between free and nascent chlorine, HENRY E. ARMSTRONG

HANDBOOK OF BOTANY Handbuch der allgemeinen Botanik. Von Prof. Dr. N. J. C. Müller. Zweiter Theil. Allgemeine Morphologie und Entwickelungslehre der Gewächse. Pp. 482, Figs. 277. (Heidelberg, 1880: Carl Winter's Universitätsbuchhandlung.)

law of Mendeljeff we have distinct proof of progressive development, but of this I hope to say more on another

occasion.

Sir B. Brodie points out in his lecture that if the symbol a'2 were assigned to hydrogen, instead of the symbol a, a different symbolic system analogous in its form to the system in vogue amongst chemists would result In the second part of the Calculus he has fully explained his reasons for adopting the hypothesis a, notwithstanding that it leads to conclusions so entirely different from those ordinarily accepted, the chief reason being that this hypothesis satisfies the so-called law of even numbers-the law that the sum of all the units of affinity in a compound is an even number. The recent remarkable discovery-probably one of the most important theoretically ever made by chemists-of the behaviour of the halogens at high temperatures would appear to furnish an opportunity of experimentally ascertaining whether Sir B. Brodie's hypothesis a is admissible, for this hypothesis would not admit of a simple resolution of the diatomic molecules of chlorine, bromine and iodine into monatomic molecules which has been regarded as the more probable explanation of the results obtained by Victor Meyer and by Meier and Crafts. Two well-established exceptions to the law of even numbers exist, nitric oxide, NO, and nitric peroxide, NO2, but as is well known, Sir B. Brodie has suggested that in these we may not be dealing with homogeneous gases, but that each is constituted of two gases which, taken together, are made up of oxygen and nitrogen, but which separately are not so made up: hypothesis a would lead to similar conclusions regarding the constitution of chlorine, bromine and iodine at high temperatures.

At present all that is established, however, regarding the halogens is that iodine begins to undergo dissociation at a temperature between 600° and 700°, and that its vapour gradually diminishes in density until at a white heat it attains not far short of half the "normal" value.

author which is to treat of all the different departments of botanical science. The first volume, which is devoted to the consideration of the Physiology and General Anatomy of Plants, was reviewed in NATURE, vol. xxi. p. 589. It is impossible to pass a more favourable verdict upon this volume than upon its predecessor. It is characterised by the same failing, namely, a want of clearness and definiteness in the statement of important facts and fundamental principles. The first section of the book is devoted to a discussion of the theory of descent, the origin of species, and the occurrence of varieties and monstrosities, with the object, presumably, of making the reader acquainted with some, at least, of the influences which determine the forms of living organisms. The account of the morphology of plants begins at p. 38, and after ten pages of general considerations the subject is actually grappled with. Prof. Müller commences with the Thallophytes, though he does not call them so, for his first section on them is headed "Der Algenstamm." It is not easy to understand what he means by the suffix "stainm"; does he mean to describe the thallus of the Alga as being a "stem," or does he use the word in the sense of "tribe"? Whichever be the true interpretation, it still remains unexplained why this word should appear as the heading of a section which treats not only of Algæ, but of Fungi as well. The prospectus of the work sets forth that the Classification of Plants is to form the subject of a subsequent volume, and there is therefore some hope that Prof. Müller will there give a classification of the Alga which is more in accordance with facts and with reason than the one which he now follows. It is impossible to imagine on what grounds the Palmelleæ, the Protococcæ, and the Volvocineæ should be united together to form the Order Palmellaceæ, and yet this is done on p. 51 of this work, although the author is evidently aware of the fact that in Volvox reproduction is effected by means of sexually produced oospores, as his account of that plant, a singularly inaccurate one be it said, on p. 62 testifies.

His account of the Lichens is not more trustworthy than that which he gives of Volvox. He appears to be halting between two opinions with regard to the burning question of the nature of these organisms, for although he states on p. 69 that the germinating spore gives rise to both gonidia and hypha, thereby implying that those cells of the thallus which do not contain chlorophyll and those which do have a common origin, yet he admits (p. 74) that the gonidia may escape from the thallus and lead an independent existence, and further (p. 84), that he has observed the formation of a lichen-thallus by the combination of algal and fungal forms which were originally distinct.

His treatment of the Cormophytes is also disappointing. If the student, anxious to become acquainted with the most recent views as to such important points as the gymnosperms of the Conifers and the morphological significance of the embryo-sac and its contents in Flowering Plants, turns to the sections of this book which profess to treat of them, he will find only a few dogmatic statements with regard to the former point, and none at all with regard to the latter. Perhaps these points may have been thought too recondite for discussion in a work which professes to be a handbook for learners of the science, but many pages are devoted to the consideration of subjects, such as the more complicated forms of phyllotaxis, which have principally a mathematical interest. Again, the morphology of the stem, of the leaf, and especially of the root, is dismissed far too summarily. It is to be hoped that these organs, as well as inflorescences, flowers, and fruits, will have justice done to them in the volume on the Classification of Flowering Plants. One further shortcoming must yet be mentioned, namely, the scantiness of the account given of the embryology of plants. This is a subject which has been much studied in recent years, and, from the title of this book, it might naturally be expected that it would give a satisfactory account of the results which have been attained. This is, unfortunately, by no means the case. Some of the facts are mentioned, it is true, but they are stated too briefly to be very intelligible, and no attempt seems to have been made to connect them together and to explain their significance.

It must be admitted that the book contains a considerable amount of information scattered through its pages, but the purely theoretical principles upon which this information has been arranged render it difficult of acquirement, and for this reason, if for no other, the book is not one which can be recommended for the use of students.

OUR BOOK SHELF

The Gardens of the Sun; or, A Naturalist's Journal on the Mountains and in the Forests and Swamps of Borneo and the Sulu Archipelago. By F. W. Burbidge. (London: John Murray, 1880.)

THIS book is the itinerary of a competent and enthusiastic botanist, whose main object was "the collection and introduction of beautiful new plants to the Veitchian collection at Chelsea," in which he so far succeeded as to add about fifty ferns to the list of those already collected in Borneo, about twenty being also new to science, and to introduce alive the giant pitcher-plant of Kina Balu (Nepenthes Rajah, Hook. f.). But these alone by no

means show the floral riches which have induced the author to use the by no means exaggerated term which here growing in mid-air "screened from the sun "Gardens of the Sun." Amongst epiphytal orchids by a leafy canopy, deluged with rains for half the year or more at least, and fanned by the cool sea-breezes or monsoons," is found the beautiful Phalanopsis grandiflora; nor in the mountain vegetation are like floral riches absent; at 5000 feet the curious pitcher-plant, Nepenthes Lowi, was found epiphytal on mossy trunks and branches, and higher still a "large-flowered rhododendron, bearing rich orange flowers two inches in diameter, and twenty flowers in a cluster." The forests and gardens of Borneo are equally rich in native and naturalised kinds of edible fruits, the mango, pine-apple, durian, rambutan, &c., being all alike plentiful and luxuriant, and, as Mr. Burbidge remarks, in some favoured districts in Malaya the forests almost become orchards on a large scale, so plentifully are they stocked.

Zoology was naturally less followed than botany, but still a collection of birds was made, notices of which, contributed by Mr. Sharpe to the Zoological Society, are appended to the volume. We however regret to find the word alligator" still constantly occurring, whilst the word "boa" is equally misleading. Crocodile and python are words which do not seem to find a home in the East, nor moreover in many books of Eastern travel. It is also quite erroneous to say that Borneo "is the only habitat of the wild elephant in the Malay Archipelago"; certainly so, at least, if we are not to exclude Sumatra from that region.

Many ethnological facts are scattered about the volume; the account of the Jakuns of Johore is taken and fully acknowledged from Maclay's memoir on the subject in the "Journal of Eastern Asia"; but the author contributes an interesting account of the method pursued by the Kadyans in playing the game of football. No one but the student of games knows how difficult it is to find much or any information on this point in most books of travel.

Tasmanian Friends and Foes: Feathered, Furred, and Finned. By Louisa Anne Meredith, Author of "My Home in Tasmania," &c. With Coloured Plates from Drawings by the Author, and other Illustrations. (London: Marcus Ward and Co., 1880.)

IT will probably be granted that there is developed in most people a fondness for certain of what we are pleased to call the lower forms of animals. Such are made pets of for various reasons: the sweetness of their song, the brightness of their plumage, the splendour of their scales -these phenomena act as causes that attract the senses. Their sometimes fond and gentle ways make of some, prime favourites, while a sense of their usefulness makes again of others indispensable companions to man.

Most of man's dumb companions have been taken from groups of animals with a more or less world-wide distribution; and it will no doubt be new to some of our readers to learn that in Australia-a country where the aborigines, for want of native pets, had to import at some time or another a dog-that there, such forms as brush kangaroos, wombats, bandicoots, and even great forest become nice, quite gentle, mannerly things, doing a little kangaroos-animals only known in these parts--can also damage now and then, it is true, by leaving long dirty tracks to bother the housemaid, like a boy home at Christmas time, or pulling up tulip-bulbs, or, worst of all, getting into the children's beds because they are comfortable. The beautifully got-up volume whose title heads this notice is written by a well-known and respected lady who has often before written pleasantly about her Tasmanian home and the bush friends she found or made there. In the present volume she writes an able defence of some of her dumb "marsupial" acquaintances, showing that

they too have intelligence, and that they exhibit at times a very respectable amount of common sense. The stories about them are strictly true, and from their very nature strictly new. But the volume tells also of many a twofooted friend, and the last few chapters almost exclusively treat of the fishes of the coast. There is much in this portion of the volume of interest to the scientific worker; there is much in every part of it to make it of value to those who care to learn something of the habits of Tasmanian beasts, birds, and fishes. One feature of the volume must be specially noticed--the eight coloured drawings, excellently chromolithographed from the water-colour drawings of the author. From a personal knowledge of the splendid colouring often present in freshly-caught tropical fishes, these plates are, we should say, by no means too brilliant. Four are devoted to some of the strange, wondrously-coloured fishes, and four to flowers, fruits, and insects.

This volume would be an excellent and not overexpensive Christmas present, which may lie on any table however select, and be read by any person however critical.

LETTERS TO THE EDITOR

[The Editor does not hold himself responsible for opinions expressed by his correspondents. Neither can he undertake to return, or to correspond with the writers of, rejected manuscripts. No notice is taken of anonymous communications.] The Editor urgently requests correspondents to keep their letters as short as possible. The pressure on his space is so great that it is impossible otherwise to ensure the appearance even of communications containing interesting and novel facts.]

Mr. Spencer and Prof. Tait

PROF. TAIT'S explanation itself shows that the word commonly applied to products of imagination, was applicable to his statements; for the only justification he assigns is that he "assumed," that is to say, imagined, that his substitution of "definition" for "formula" must have been the ground of offence. How inadequate a plea this is, will be seen on re-reading the questions I put, which were these:

"He [Prof. Tait] says that because he has used the word definition' instead of formula,' he has incurred my 'sore displeasure and grave censure.' In what place have I expressed or implied displeasure or censure in relation to this substitution of terms? Alleging that I have an obvious motive for calling it a formula,' he says I am indignant at its being called a definition. I wish to see the words in which I have expressed my indignation; and shall be glad if Prof. Tait will quote them. He says:-'It seems I should have called him the discoverer of the formula!' instead of the inventor of the definition.' Will he oblige me by pointing out where I have used either the one phrase or the other?"

Every reader would infer that, for these specific statements made by Prof. Tait, there are specific foundations, which could be named when asked for. He does not name them, for the sufficient reason that they do not exist. Unable, as he says, to see in the passages I quoted from him, anything else to call for "censure" (a strange inability !), he "of course" assumed that this change of terms was the ground of censure. And the assumption thus made, is the only warrant he assigns for these positive assertions.

This is not all, however. Prof. Tait says:-"I could not have ventured to suppose that Mr. Spencer did not even know that he was in the habit of saying formula rather than definition? This naïve confession cannot but be correct." Of Prof. Tait's motive for putting this statement of mine in italics and calling it naive, the reader may judge for himself. How entirely correct it is, and how well Prof. Tait might have "ventured to suppose it, will quickly appear. For there is proof that I am not in the habit of always saying formula rather than definition; and Prof. Tait had the proof before him. In the note on page 565 of the Appendix forming the pamphlet in question-a page which Prof. Tait must have read, since it concerns Mr. Kirkman and himself -I have used the word "definition." So that not only had Prof. Tait no evidence on which to base his distinct statements,

but there was under his eyes positive evidence which negatived them.

Very possibly it will be said that the question about my uses of these words is a trivial one. But this is not the question. The question is whether it is allowable to make an opponent look absurd by ascribing to him, in a quite positive way, things which he has neither said nor implied; and that, too, when he has implied the contrary. HERBERT SPENCER

Criterion of Reality

WILL you kindly allow a learner to ask for the criterion according to which Kinetic Energy and Work are real things, while Momentum and Force are unreal? Prof. Tait says m and wh express real things, but me and wt unrealities (NATURE, vol xxiii. p. 82).

If wt be as unreal as is the product of a quart into an acre," how is it that wh is real? The illustration of quart and acre is as applicable or inapplicable to the one as to the other. In both cases we take the product of two numbers, not two concrete magnitudes, which of course it would be absurd to speak of multiplying together. In one case the product is the number of units of Momentum, in the other case it is the number of units of Kinetic Energy. If it be said that a thing is real if its quantity cannot be altered, and vice versa, why is my said to be real, and my unreal? They vanish together. When Prof. Tait asserts"there is no such thing as Force," "it is merely a convenient expression for a certain rate" (NATURE, vol. xiv. P. 459), he seems, if I may venture to say so, to confound the measure of Force with Force itself, and to lay himself open to Mr. Spencer's comment that "a relation changes the state of a body." Certainly mu is not a thing, but neither is m2 a thing: yet the latter is the measure of something which Prof. Tait asserts to be "as real as matter itself": why is not that of which the former is the measure equally real? E. G. Bardsea

[What Prof. Tait asserts may be correct or not, but it is selfconsistent. He asserts in his lecture on "Force" (NATURE, vol. xiv. p. 462) that matter and energy must be looked on as real things, because we cannot change the amount of either. Such expressions as mv2, and wh, are to be considered as wholes, not as products of two or more factors. This separation into factors (where one is mv, or w, for instance) he asserts to be a relic of the old erroneous belief in the trustworthiness of the impressions made on the "muscular" sense.-ED.]

Landslips

IN NATURE, vol. xxii. p. 560, I pointed out that landslips often occurred in the Salt Districts. I did not then expect that I should so soon be able to refer again to the subject; but on December 6, at an early hour in the morning, one of the largest subsidences and landslips ever known in Cheshire occurred. I pointed out that whenever fresh water reaches the rock salt it dissolves it. In certain districts in the immediate neighbourhood of Northwich the ground is completely honeycombed with rocksalt mines that had been worked out and abandoned. Into many of these fresh water had penetrated, and had become by solution strong brine. This brine has of late been extensively pumped up, and many of these extensive cavities had become nearly empty. The thin crust of rock salt forming the roof of these old mines had become gradually thinner, owing to its solution by water, and on Monday morning the roof of one pit gave way, and let the superincumbent earth down into the mine, rifting and opening the ground to the surface. The surface rift passed across the bed of a large brook, and the water of the brook ran through the crevice into the mines below. In a short time the water made a more extensive cavity, and as the brook was cut in two about 200 yards above its entrance into a large lake that was drained by the Weaver River, the water in the lower portion of the brook and of the lake, as well as of the Weaver, commenced to return and run down the enlarged cavity. For four or five hours this return stream increased in velocity, pouring down the crater-like hole. Notwithstanding the water of the brook and the return water, as well as a large body of water from another small lake entering this cavity, the water standing in the funnelshaped hole gradually lowered. The velocity of both portions of the brook increased, and such was the force of the water that the bottom of the brook for 100 yards was scooped out from 2 feet in depth to 10 feet, and the banks were washed away,

making the brook from 30 to 40 feet wide instead of 20 as at first. The quantity of water thus rushing down for twelve hours from the commencement would be fully 600,000 tons. The water in one direction over a surface of 160 acres was lowered one foot in the space of three hours. Shortly after this water commenced to rush below it made its way through a weak portion of a barrier wall into a rock salt mine that was being worked. This mine, extending over fifteen acres, and having a worked-out depth of eighteen feet, was completely filled and all the tools, materials, waggons, tramways, &c., entirely lost. It will be quite impossible ever to pump out the water. Besides this mine, all the old abandoned mines were filled, and the brine, which stood at 100 yards from the surface on the Sunday, stood at 24 yards on Monday night. The water being fresh, great damage was expected by the solution of the salt. This soon occurred, for an old mine that fell in forty-two years ago, and the cavity of which had been filled with water, gave way, and suddenly the whole land over a circle of about 500 feet in diameter sank, and a large portion of water escaped into neighbouring pits. The ground cracked and rifted and subsided, and a length of road of 160 yards was destroyed, as also pipes conveying brine to the salt works. A large reservoir holding brine was split across and all the brine let out; the rending of the earth passed through two kilns of bricks, dropping one-half of the kilns at least 2 feet. On the Monday afternoon a tall chimney 90 feet in height became affected, and in a few hours fell with a great crash. The air that had filled the cavities below was forced out by the inrush of water, and caused all the pits and brooks near to bubble and boil violently, whilst in some of the rifts where water occurred miniature mud geysirs were formed, throwing up mud 10 or 12 feet high. These appearances extended over a district between two brooks for the space of 2000 feet. On Wednesday night a large hole 30 yards in diameter and 30 yards deep fell in, and more subsidences are daily expected, as the fresh water will eat away the pillars supporting the roofs of the abandoned mines.

The cavity formed on Monday is full of water, and the brook now runs through it. Some idea may be formed of it when I mention that it is crater-like, and of about 200 feet in diameter. On sounding it on Wednesday I found a depth of 78 feet of water in the centre, and various depths from 70 to 60, 50, and so on to about 12 feet at the margin. On Sunday, on the spot which is now 78 feet, there was a sandbank with its surface above the water.

Serious injury has been done to one set of salt works, and five sets are stopped for want of brine, the pipes being broken and the road destroyed.

As the salt trade increases these enormous sinkings keep increasing, and become more alarming in their character. Brookfield House, Northwich

THOS. WARD

The Geology of East-Central Africa and the Subterranean Forest in Bombay

IN Mr. J. Thomson's very interesting "Notes on the Geology of East-Central Africa" (NATURE, vol. xxiii. p. 104) he remarks that doubtless the immense development of volcanic rocks described by myself (and I may add by several previous explorers) in Abyssinia is of the same age as the volcanic rocks at the Cape of Good Hope, assigned to the Trias.

Mr. Thomson has, I think, overlooked the circumstance that whatever may be the age of the Cape volcanic rocks, the teaks of Abyssinia cannot be older than Jurassic. As I have shown (Quart. Four. Geol. Soc., 1869, pp. 403, &c., and "Geology and Zoology of Abyssinia," pp. 184, &c.), there are in the Abyssinian highlands two groups of bedded dolerites and trachytes, the upper of which rests unconformably on the lower, while the latter overlies limestone with Jurassic (Middle Jurassic) fossils.

I trust that Mr. Thomson will pardon my suggesting the possibility of the Tanganyika sandstones being river valley deposits, like the Gondwana series of India, rather than lacustrine. I may be mistaken, but the description appears to me to indicate beds coarser than those usually deposited in an extensive lake basin.

In the same number of NATURE, p. 105, is a brief notice of a "Subterranean Forest in India." As I understand the account given, the forest should perhaps rather be termed submarine than subterranean. My object in calling attention to this notice however is to point out that a previous description of the same formation was published in the Records of the Geological Survey

of India for 1878, vol. xi. p. 302. This account is by Mr. G. E. Ormiston, Resident Engineer, and agrees in all essential particulars with the note in NATURE. I appended a few remarks on the geological bearing of the discovery. The "forest" has clearly been depressed, whilst neighbouring tracts in Bombay island appear to have been elevated in comparatively recent times. W. T. BLANFORD

Dr. Siemens's Gas-Grate

HAVING endeavoured for some years past to heat my study by gas appliances, and having utterly failed in obtaining a comfortable temperature of 60°, as a last effort to accomplish my object I had fitted into an ordinary grate Dr. Siemens's arrangement of copper and iron, the construction of which was communicated to the public in the pages of NATURE, vol. xxiii. p. 25. Before giving the results of the trial of Dr. Siemens's gas-grate I may mention in what way my former gas-stoves failed. My first gasfire consisted of gas and asbestos, but this gave out fumes which were quite intolerable; my second trial was with a gas-stove reflecting heat from a copper lining; this not only failed to warm the room, but was a cheerless and grim apology for a fire, and to obtain even a moderate degree of temperature a constant and expensive consumption of gas was necessary. With Dr. Siemens's gasgrate all that is required to produce a good cheerful fire radiating heat to all parts of the room, and maintaining a temperature from 60 to 62°, is to turn on the gas full for about twenty minutes, and as soon as the lower stratum of coke becomes incandescent, the gas may be quite turned off, the fuel, whether coke or anthracite, continuing to burn for five or six hours without any further expenditure of either gas or fuel.

If the fire is required for a longer time, or if at any time a more rapid combustion is wanted, it is only necessary to turn on the gas again for a few minutes and add more fuel. This is my experience of Dr. Siemens's gas-grate, and I consider it a great boon to householders who desire well-warmed rooms combined with economy. After the lucid description of the gas-grate given by Dr. Siemens in NATURE, it would be presumption in me to discuss the scientific explanation of its action; I shall only, in conclusion, venture to claim for it the following advantages which I believe it to possess over every other kind of gasstove yet invented :

:

1. It gives a clear, smokeless, cheerful fire.

2. It is most economical, and very soon pays the cost of the construction.

3. Being absolutely smokeless, contributes nothing to that constituent of our London fogs which renders them injurious in so many ways.

This last advantage, if multiplied by every householder at an outlay of 25s., adopting a cheaper modification than the copper and iron gas-grate, we should before very long observe a marked change for the better in our London atmosphere; and the darkness, dirt, and destruction of property with which we Londoners are annually afflicted, would be things of the past. December 13

R. DOUGLAS HALE

Geological Climates

I HAVE just read Mr. A. R. Wallace's letter in NATURE, vol. xxiii. p. 124, but as I have not yet seen his book, “Island Life,' although my bookseller had promised it, I shall defer my reply in NATURE until I shall have made myself master of his ideas.

For the present I shall only say:-1. That Mr. Wallace's proposal would benefit the Polar regions but not Bournemouth.

2. Mr. Wallace omits all mention of the return cold currents which the admission of two new Gulf Streams into the Arctic regions would produce. These currents would seriously lower the temperature of China and Japan; and also of the Ural Mountains and east of Europe.

Trinity College, Dublin, December 10

SAMUEL HAUGHTON

SOME weeks since the Rev. Prof. Haughton took exception to a brief letter of mine, in which I suggested that as a bamboo flourishes in Cooper's Hill College garden, in a northern aspect winter after winter, it could be used effectually in an argument relating to geological climates. The bamboo being found in torrid India now, that at Cooper's Hill, if found in a future period, would, according to some geologists, indicate that the valley of the Thames was tropical formerly. My letter was