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to be found, while in Darwinella, triaxon horny spicules abound.

Very interesting accounts are given of the connective tissue, muscle cells, and nervous system. Stewart's account of the "palpocils" is accepted; and, although Prof. Stewart's specimens are the only ones which show these organs properly, yet Lendenfeld thinks that, when groups of converging sense-cells are observed (in sections) below the continuous surface, these may be regarded as the cells of a "retracted" palpocil.

The researches of the author have thrown but little fresh light on the subject of the occurrence of the strange "filaments" in the species of the genus Hircinia; these filaments are generally more abundant in the superficial layer than in the interior of the sponge. They may be isolated, or arranged in bundles of varying thickness, in which they are parallel. Such bundles are particularly conspicuous in H. gigantea, where they form a pretty uniform network which pervades the whole of the sponge. The filaments are never straight: they may be continuously and simply curved, or they are undulating. The latter form of curvature is particularly frequently observed in the filaments which are joined to form large bundles. While their abundance is subject to variation, no case of a sponge with but a few isolated filaments is on record. No apparent young stages of these filaments have been seen. Schulze's researches enabled him to make no positive statement concerning them, but they at the same time demonstrated that "no cellulose is contained in them, that they have no trace of true cellular structure, and that they contain a great deal of nitrogen (9'2 per cent. of their substance), and that they are not Algæ. The resistance of the filaments in boiling alkali is against their being ordinary Fungi, while their general chemical composition indicates no relationship to the ordinary sponge skeleton." As to the very minute dumb-bell shaped structures observed by Poléjaeff, and considered by him to be young stages of the filaments, Lendenfeld thinks that this is extremely doubtful, "particularly as nobody besides Poléjaeff has seen them in H. friabilis or any other sponge." But is this so? for in another paragraph we read :

:

"The spherical bodies which Schmidt and Poléjaeff consider as young stages of these filaments-in fact, as terminal knots, either dropped off, or on the way to produce a filament-have also been observed and carefully studied by Schulze, who considers them as monocellular Algæ, which have nothing whatever to do with the filaments."

Lendenfeld says that "no trace of filaments or 'spores can be detected in the young embryos which are often found in specimens of Hircinia."

On the physiology of the group, this monograph throws but little light :

"Our knowledge of the vital functions of sponges is at present exceedingly unsatisfactory. We do not even know which parts of the sponge absorb nourishment, or, in fact, what kind of food the sponges take in. We are equally ignorant concerning their respiration and secretion."

There being then no facts to serve us as guides to knowledge, the next "best thing" is to have recourse to imaginations, and our author "thinks" that "it is by no

means unlikely that the sponges may exclusively ab liquid food-that is to say, organic substances disson in the water which is continuously passing through canal system. All the other organisms in which arran ments are made to insure a continuous water curre I refer to the higher plants-absorb exclusively nouri material in solution (the absorption of gaseous forci plants does not concern us here). The existence of traversing canal system and a continuous water cr seems to me to point to the nourishing material sponges being in solution in the sea-water. The numero fine sieves and filter arrangements generally, and the me fact that the water always enters through the smaller ho and is expelled through the larger, clearly shows tha sponges are not desirous that large food-particles shoc enter their canal system."

Even granting that the word "exclusively should! after the word "material," we do not quite understan the comparison of the well-known facts of plant physio as they are presented to us in the above extract, nor how it helps us to an understanding of how the sp adds to its protoplasm; the undoubted power poss by some of the sponge-cells to lay down silica, lime, à quite different functionally from the phenomena attendgrowth and development, using these terms in Here Spencer's sense; but once set a thinking, our aut proceeds, and telling us that a "tape-worm is an u which takes up liquid food, and which has no spe digestive apparatus, and that it evidently takes up a quantity of material from the surrounding chyle thro the apparently indifferent cylindrical ectodermal ep. lium cells; that the excess material and waste prod are got rid of by the nephrydia," he goes on to that he is inclined "to think that in sponges we may ha a similar mode of absorption of nourishment"; but tr where are the nephrydia or their analogues? and thinks again "that it is not impossible that the cla chambers may be partly analogous to the nephryda the Coelomata, and that the collar-cells may, bes performing other functions, also secrete the unre However uncertain, he adds, this hypothesis may app "I think there can be no doubt that there is more probility in it than in the view, held by Carter and others

the older authors, that the ciliated chambers are mere digestive apparatus." This seems a rather dreamy h thesis, with no facts for its foundation; but it is butt to remark that it comes at the very end of a volume wh is a record of numerous and important observations

Under the headings variability, parasitism, and biosis, many interesting details are given. The aut thinks that certain forms of Aulena and Chalinops imitate "certain siliciferous Cornacuspongia. Ths sponges have descended from those which they imter and, whilst they have lost the spicules in the fibres, the have retained the outer appearance of their better tected ancestors in a most striking manner.” Apparent) "the primordial sponge ancestors were free-swimm and had no skeleton. Some produced a calcare others a siliceous skeleton; in both the subseque development, the formation of ciliated chambers, a the ancestors did not possess, and the fixing of the and rays of the spicules, were the same. The prince Silicea had indifferent irregular spicules, from which th

on and the tetraxon spicules were developed by an captation of the divergent development of the canal tem. The primordial forms of both lived in water a silica, and certain forms of both lost their spicules consequence perhaps, of rising from deeper to shallower water, where silica is more scarce. In both, some forms are lost the skeleton altogether, while others have reed it gradually by spongin."

While acknowledging that some authors whose opinions carry great weight, such as Balfour, Bütschli, and as consider the sponges as a separate group, equal valce to the groups Protozoa and Metazoa, Lendenfeld t but conclude that the sponges are, without doubt, ana, and certainly Coelentera, in the sense of being ided with a simple body cavity.

The last twenty pages of the work are devoted to a nopsis of all the known sponges, giving the classes, Lines, orders, and genera. In this extremely useful list Lere is a short analysis of the families and orders, wach is based on the labours of Vosmaer, Ridley, Dendy, Sollas, Schulze, added to those of the author's own. The author ends his treatise with the statement that "Now Mat all the groups of sponges have been thoroughly investigated, we may consider our knowledge of their phylogenetic affinities established on a satisfactory footing" po; but it seems well to call to mind the statement th which he closes his short preface, and with which we feel the more inclined to agree, our present knowledge (the group... has only just arrived at a stage corremang to the knowledge of the higher animals of half Tentury ago" (p. 5).

in concluding our only too brief notice of this important work, for which all workers on the group must thank Dr. Indenfeld, we may mention that the sponge portraits for the most part photo-lithographs taken from the rnal types; though in a few cases, where no good Demens were available, the lithographic illustrations are from drawings.

THE FLORA OF SUFFOLK. The Flora of Suffolk. By W. M. Hind, LL.D., Rector Honington, assisted by the late Churchill BabingPUB, D.D., F.L.S. With a Chapter on the Geology, Camate, and Meteorology of Suffolk, by Wheelton Hind, M.D., F.R.C.S. Pp. 508, with a Map. (London Gilbert and Jackson, 1889.)

UFFOLK is a characteristic lowland maritime English county, the flora of which, at the present day, tains absolutely no infusion of the boreal element, area is about 1500 square miles. The whole surface flat, without any prominent rocks. It is underlain by uk, which, in the north and west, lies immediately below the subsoil, but, in the south and east, is covered Tertiary and Glacial deposits, which at Harwich have en found to reach a thickness of 1000 feet before the Walk is reached. In White's history of the county, its s are classified into three groups: heavy lands, in each clay predominates; mixed land, common mixed rich deep moulds, fen-lands, and rich marshes; and lands, consisting of sand over chalk. To the first belong the soils of the western two-thirds of the

The

county, except in the extreme north and near the coast. The mixed lands are found-one portion east of the heavy lands between the Orwell and the Stour; a second in the north, between Halesworth and Yarmouth; and a third west of the heavy lands between Holston and Newmarket. The sandy, or light, soils are in the extreme north-west, in what is called the "Breck district," between Thetford and Mildenhall, where are found the rarest plants of the county, such as Veronica hybrida, V. triphyllos, V. verna, and Apera interrupta. The coast is remarkable for the extent of its tidal estuaries and bays, creeks and havens. There are no cliffs of any considerable height, but a great extent of sand and shingle. beach at Orford, where grows the great mass of Lathyrus maritimus, the seeds of which saved the life of many poor people in a famine in the middle of the sixteenth century, is said to have the greatest breadth of sand any. where on the English coast. The rivers are shallow streams with slow currents. In the north-east there are several lakes of brackish water, not so well known as the Norfolk Broads, of which Braydon Water covers 1200, and Thorpe Mere 1000, acres. The fresh-water lakes of the county are few and small. There is a considerable area of fen- and marsh-land, both in the north-west and east, so that we get in the county all the conditions that produce a rich low-country flora, and, superadded to the common lowland plants, rarities characteristic of chalk country, the seashore, and fen-land ditches and marshes.

The country is so easy of access from the centres where have lived many of the best botanists of bygone time, such as London, Cambridge, Yarmouth, Norwich, and Saffron Walden, that the principal features of its botany have long been known, and many excellent botanists, from the time of Buddle down to the present day, have resided within its compass. The father of Suffolk botany was Sir John Cullum, F.R.S., who lived near Bury St. Edmunds, and kept a diary between 1772 and 1785, in which he has recorded the occurrence of upwards of 500 plants. To his son, Sir Thomas Cullum, F.R.S., who was also an enthusiastic botanist, Sir J. E. Smith dedicated his "English Flora." In the present work there is not only a full general history of the progress of Suffolk botany, but, under each plant, the name of its first known collector is registered. The first "Flora" of the county was published in 1860. It was carried out mainly by the exertions of the late Mr. E. Skepper, working under the superintendence of Prof. Henslow. After it was published, Mr. Skepper made a great many notes for a new edition, but he died in 1867. For several years the Rev. Churchill Babington, who settled in the county in 1866, paid attention to the subject. In 1875, the Rev. W. M. Hind, a very competent botanist, well known by his "Flora of Harrow," settled in the county, and Dr. Babington sought and obtained his assistance to carry on the work. Dr. Babington died early in the present year.

The

The bulk of the book is, of course, occupied by the enumeration of the species and an account of the distribution and special localities of the varieties. county is divided into five districts, and the distribution of the plants is traced through them. Only the Phanerogamia and Vascular Cryptogamia are dealt with, bu the mosses of the county have also been well worked.

There is also a detailed tabular comparison of the plants of Suffolk with those of Norfolk, Cambridgeshire, and Essex, and a short chapter on the characteristic plants of the different soils of the county, which will be found very interesting to students of plant-dispersion. The chapters contributed by Dr. Wheeler Hind, the son of the editor, on the geology, physical geography, and meteorology of the county are very full, clear, and add greatly to the interest of the book.

One of the most interesting circumstances in the county flora is the occurrence of several maritime plants far inland. In the Breck country, between Thetford and Mildenhall, grow Vicia lutea, Erythræa littoralis, Rumex maritimus, Carex arenaria, Phleum arenarium, and Corynephorus canescens. These are all seaside plants, and their occurrence fifty miles inland is accounted for by Prof. Newton and the editor by supposing that an arm of the sea has penetrated here southward from the Wash at a comparatively recent period.

It is in Norfolk and Suffolk that the most valuable observations have been made, by Mr. Clement Reid and his fellow-workers, in illustration of the time of origin of our present British flora. The Cromer plant-bed extends into Suffolk, past Pakefield, to Southwold and Dunwich. This is pre-glacial, and yet, out of upwards of forty plants found in it that have been clearly identified, there are only two that are not British now-the spruce fir and Trapa natans. At Hoxne, near Diss, lacustrine deposits have been found resting on a bed of boulder clay, but beneath beds which contain bones of the elephant. In these are contained Salix polaris, S. Myrsinites, Betula nana, Hypnum sarmentosum, and a Pinus which is probably sylvestris—all characteristic Arctic-Alpine types, associated with many lowland plants which grow unchanged in Suffolk at the present time. A chapter in the book contains a list of all these plants, but their geological position is not clearly explained.

It will be seen that this is a very interesting and complete county flora, and that it is worthy of being studied carefully by all who are interested in the distribution of our indigenous plants. J. G. B.

THE MANUFACTURE OF IRON AND STEEL. Iron and Steel Manufacture. By Arthur H. Hiorns. (London: Macmillan and Co., 1889.)

This volume is meant yoccupy that position.

HIS volume is meant as a text-book for beginners, It is full of information, and information of the very kind which the student should possess before entering upon the study of the greater works of Percy or Fhillips. On the other hand, those already engaged in the metallurgy of iron and steel will find in these pages much that may be referred to.

The book begins with a brief history of the processes that have been employed down to our own time, the landmarks in which are Dud Dudley's successful attempts to smelt with coal at the beginning of the seventeenth century; Cort's introduction of the puddling process in 1784; Neilson's recommendation to use hot blast in 1828; the revolution produced in the iron trade by the invention of the Bessemer steel process in 1855, as supplemented by R. F. Mushet, of the Siemens furnace and steel

process, and finally of Thomas and Gilchrist's bar process.

The chapter which deals with chemical principles an. changes, inserted for the benefit of those having a lime. knowledge of chemistry, is valuable on account of t simple manner in which it is written; this is particular the case as regards oxidizing and reducing agents, the examples given of oxidation and reduction showing t reactions very clearly. A chapter is devoted to the definition of metallurgical terms, refractory materials ar fuel, another to the ores and alloys of iron, and then = description of the various processes employed in the met lurgy of iron and steel is given, attention being prett equally divided between the two metals.

The most ancient and most difficult method of e tracting iron from the cre is what is known as the dre method, and the author explains clearly the two causes of its failure, whether in the case of the old Catalan or an of the modern processes, and the reason why the bla furnace, although an indirect, has proved so successfa's method. These two causes are "the easy oxidation iron by carbonic acid and water, at the temperature: which ferrous oxide is reduced to the metallic state by carbon, carbonic oxide, or hydrogen, and the facility wit' which iron at a red heat combines with carbon."

The preparation of the ores for reduction in the blas furnace and their treatment therein are next broug forward, the advantages and disadvantages of the ho blast, the utilization of waste gases, the dimensions and form of blast furnace and subsidiary subjects bec treated of.

The metal being now in the state of pig-iron, the mean of refining and puddling are described; the various ar rangements are set forth by which attempts have bee made to effect the work of the puddler by mechanica means, whether by automatic rabbles or rotatory furnaces. and their relative advantages and disadvantages. A chap ter is devoted to the treatment of puddled iron under the hammer and in the rolling mill, and to the tinn and galvanizing of iron.

Leaving the subject of malleable iron, the author ne considers the question of iron-founding. He describes the cupola furnace in which the pig metal is fused; and tat various methods of moulding and casting, and the brand. of pig-iron used for different purposes, are treated of

About a third of the book is devoted to the consider tion of steel; it is in this branch of the treatment of that the greatest development has occurred of late years. and the book under review treats of all the moder practice. It is pleasant to find, too, in the preparation o an elementary work, that constructive perspective ha been employed. Modern processes are not brought prominence simply because they are modern, and ancien methods are not thrown into the shade if still employe Amongst the latter we find full attention given to the cementation process, and crucible steel; whilst a chapt is devoted to each of the processes of Bessemer a Siemens. The book finishes with a chapter on ster casting and on testing.

The volume before us is intended to assist pup preparing for the ordinary grade examinations of the C and Guilds of London Institute, and its author-*** principal of the School of Metallurgy in connection with

the Birmingham and Midland Institute-is to be congratulated on the good work he has done in this connection. The book is illustrated with 72 figures, which agree with the simplicity and clearness of the diction, and questions are found at the end of each chapter, which have been well prepared to test the learner's apprehension of it, contents. We are pleased to be able to recommend ims little work, as a foundation for the study of the metallurgy of iron and steel.

OUR BOOK SHELF.

On the Creation and Physical Structure of the Earth. By J. T. Harrison, F.G.S., M. Inst. C. E. (London: Longmans, 1889.)

THIS book brings to mind one of the most winning of the raganes of childhood. A bright child of an inquiring tim will sometimes sit with comical sedateness listening to the talk of its elders. It may afterwards be overheard repeating to one of its playmates, or to some lucky adult who has the knack of winning its confidence, such derbed scraps of the conversation as have found a reting place in its little brain; and, conscious even at its ear age of the necessity of some continuity in a narrative, filing up the gaps with inventions or criticisms of its own, charming every way, but mainly on account of their utter want of connection with the subject of the converaton which it is attempting to report. So our author has listened to the teaching of many geologists, and has illed many detached passages from their writings: these be repeats to the world in a book, printing between them Comments and lucubrations of his own, about as innocent and as little apposite as the child's prattle-hardly so using, however. The following passage is a fair sample of the writer's own share in the book. "The termination of the Secondary Period, which introduced these altered conditions of the surface of the northern hemisphere, was really the commencement of what is called the Glacial epoch in Europe. We have noted signs of glaciation Conng the deposition of the upper chalk in India and North America, but now the conditions which induced that daciation are extended in such a manner as to unite hese districts, and produce that enormous accumulation of snow and ice at the North Pole, the weight of which in the Miocene epoch depressed the crust in that region and upheaved the mighty mountain ranges to which I have just referred.

The book bristles with cataclysms and catastrophes. The shifting of a thin crust on an internal nucleus which it does not fit, and incessant protrusions of granite, are invoked to account for phenomena which every-day people still persist in thinking are satisfactorily explained by every-day causes. But the author is one born out of due time-two centuries too late. How he and Burnet would have enjoyed a crack together! But there is this To be said, the "Sacred Theory of the Earth" is Burnet's WD: the staple of the present work consists of extracts from the works of others. The mottoes are verses from the first chapter of Genesis, but their relevancy to the bject-matter of the chapters which they head is not

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A. H. G. Through Atolls and Islands in the Great South Sea. By F. J. Moss. (London: Sampson Low, 1889.) Ma Moss-a member of the House of Representatives, New Zealand-started from Auckland, in September 1886, in the schooner Buster, for a voyage among the islands and islets of "the outer lagoon world." He was absent seven months, and during that period he crossed the equator six times, and visited more than forty islands among the least frequented groups. In the present

volume he sums up the impressions produced upon him by what he saw and heard in the course of his voyage. Mr. Moss, in dealing with matters which really interest him, shows that he is an accurate observer and a man of sound judgment. His style, although plain and unpretending, is well fitted for the task he has fulfilled. The best parts of the book are those in which he tries to convey some idea of the daily life led by those natives whose customs he had an opportunity of studying. He appreciates warmly some aspects of the various Polynesian types of character, but thinks that the people are likely to degenerate rapidly, unless they can be provided with a better class of native teachers than most of those to whom the duty of guiding them is now intrusted. What is needed, he thinks, is, that the islanders shall have in their work and in their amusements freer scope for the imaginative powers with which they are endowed, and the exercise of which is too often foolishly discouraged. Everything Mr. Moss has to say on this subject deserves the serious consideration of those to whom his warnings and counsels are either directly or indirectly addressed.

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 intended for this or any other part of NATURE, No notice is taken of anonymous communications.] Who Discovered the Teeth in Ornithorhynchus ? IN NATURE of November 14 (p. 31), Profs. Flower and Latter criticise my note which appeared the week previous (November 7. p. 11), concerning the discovery of teeth in the young Ornithorhynchus. They promptly dismiss my claim that Sir Everard Home discovered the teeth of the young Ornithorhynchus, by stating that the structures described and figured by Sir Everard are the well-known cornules of the adult animal.

If they will take the trouble to turn to the plate cited by menamely, Plate lix. of the second volume of Home's "Lectures," 1814-and will read the accompanying explanation, they will see that Home was familiar with the teeth of both the young and the old animal.

For the benefit of those who may not have access to Home's "Lectures," I here reproduce outline tracings of two of his thorhynchus-the "first set," as Home says, figures. Plate lix. Fig. 2, shows the teeth of the young Orni66 to show that there are two grinding teeth on each side." The next figure is a similar tracing from the succeeding plate in Home's "Lectures" (Plate Ix.), which represents, to again use Home's words, "the under jaw of the full-grown Ornithorhynchus paradoxus, to show that there is only one grinder on each side." Both of these figures are natural size.

In the face of these facts, further comment seems unnecessary. I admit, of course, that Home did not discover the chemical composition of the teeth of the young animal-this was Poulton's discovery. C. HART MERRIAM. Washington, D.C., November 30.

[We do not reproduce the outlines sent, as anyone interested in the subject may see the originals, not only in Home's "Comparative Anatomy," but in the Philosophical Transactions, where they first appeared.-ED, NATURE.]

I SHOULD be very sorry to deny the credit of any discovery to Sir Everard Home, or anyone else, if any evidence could be shown of its having been made. Of the figures cited by Dr. Hart Merriam, that of the younger animal seems (as far as can be judged from the roughly executed engraving, with the assistance of the descriptive text) to represent the horny plates, showing the hollows from which the true teeth have recently fallen; that of the old specimen, the same plates after they are fully grown, and their surfaces worn down by attrition. This difference led Home to conjecture that these plates were changed during the growth of the animal-a view which was corrected by Owen ("Comp. Anat. of Vertebrates," vol. iii. p. 272), by the statement

that "each division or tubercle of the [horny] molar is separately developed, and they become confluent in the course of growth.' By the way, no one can have been better acquainted with the work of Home than his successor in the Hunterian Chair, Sir Richard Owen; and yet, in his numerous references to this subject (Art. "Monotremata," "Cyclop. Anat. and Physiology"; "Odontography"; "Comp. Anat. of Vertebrates," &c.), no trace is shown of any knowledge of a discovery which could not have failed to have interested him, if it had been made before his time.

If a cursory perusal of Sir Everard Home's first account of the mouth of the Ornithorhynchus (in the Philosophical Transactions for 1800), or any interpretation placed upon his figures, might lead anyone to infer, with Dr. Merriam, that the real teeth of the young animal had been discovered at that time, the best possible authority may be conclusively cited against such an idea, no other than that of Home himself, who, in his later description of the same specimen ("Lectures on Comparative Anatomy," 1814), describes the organs in question as "the first set of cuticular teeth”—an expression quite incompatible with their being the teeth described by Mr. Poulton and Mr. Oldfield Thomas. It really seems superfluous to have to remind a zoologist of such high repute as Dr. Hart Merriam that the difference between teeth with the structure and mode of growth which characterize these organs in the Mammalia generally, and the horny epithelial plates of Ornithorhynchus, is not merely one of "chemical composition." W. H. FLOWER.

The Pigment of the Touraco and the Tree Porcupine. ATTENTION has been lately again directed to the red pigment in the wing feathers of the touraco, which has been stated by several observers to be soluble in pure water. Prof. Church, who was the first to experiment upon this pigment (The Student, vol. i., 1868; Phil. Trans., 1869), quotes Mr. Tegetmeier and others, to the effect that this pigment can be washed out of the feathers by water. Later, M. Verreaux (Proc. Zool. Soc., 1871) confirmed these statements from his own experiments while travelling in South Africa; attempting to catch one of these birds whose feathers were sodden with rain, he found that the colour stained his hands "blood-red." A few years ago Prof. Krukenberg ("Vergl. Phys. Studien ") took up the study of turacin-as Prof. Church termed the pigment-and added some details of importance to Prof. Church's account; Krukenberg, however, contradicted certain of the statements quoted by Church with reference to the solubility of turacin in pure water, remarking that the pigment in the dead bird is insoluble in water. writer in the Standard of October 17 is able "partially to confirm" the assertion that turacin is soluble in pure water. Seeing that there is some conflict of opinion with regard to this matter, I think it worth while to state that I found it quite easy to extract with tap water (warm) some of the pigment from a spiritpreserved specimen of the bird; only a very small amount couid be extracted in this way, and the feathers were not perceptibly decolorized even after remaining in the water for a fortnight. I also experimented upon a feather just shed from one of the specimens now in the Zoological Society's Gardens; this was steeped in water for some time without any effect being visible, but after a period of two days the water became stained a very faint pink. The touraco, however, is not a unique instance of a terrestrial animal with an external colouring matter soluble in water. I am not aware whether other cases have been recorded, but I find a pigment of a similar kind in a South American tree porcupine (Sphingurus villosus).

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This porcupine has bright yellow spines which are for the most part concealed by abundant long hair.

therefore, a considerable probability that in the living ani the pigment is also soluble in water. I believe that this yea pigment is undescribed, but I have not yet completed my of it; in any case, it is not zoofulvin or picifulvin, or "lipochrome." FRANK E. BEDDARD

Exact Thermometry.

IN the account which Prof. Mills has given (NATURE, Dec ber 5, p. 100) of M. Guillaume's "Traité pratique de la Ther métrie de précision," the permanent ascent of the zero-poitt a mercurial thermometer, after prolonged heating to a high te perature, is stated to be due to compression of the bulb-renderet more plastic by the high temperature-by the external ata spheric pressure.

The constant slow rise of the zero-point of a thermometer: the ordinary temperature is mentioned by Prof. Mills; and late Dr. Joule's observation of this change in a thermo during twenty-seven years is specially alluded to. It may imagine, be taken for granted that after the lapse of a sute length of time-possibly many centuries-a final state of eq brium would be attained; and it has always appeared to t that the effect of heating the thermometer to a high temperature is simply to increase the rate at which this final stateapproached. It is my impression that, owing to the more rap cooling of the outer parts of the bulb after it has been blown, the inner parts are in a state of tension, as, to a very exaggera degree, in the Prince Rupert's drops; and that it is the graha equalization of the tension throughout the glass that causes t contraction; in other words, that the process is one of annealing.

This explanation appears to be supported by the facts-'t that when a thermometer is exposed for a long time to a g temperature, the zero-point rises rapidly at first, then me more slowly, and finally becomes constant or nearly so; (2) t the higher the temperature the more rapidly is this state (equilibrium attained. I do not know of any experime evidence that the rate of ascent is influenced by changes external pressure, and it seemed to be desirable to test the point.

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In order to do this I have exposed three thermometers, A, B and C, constructed by the same maker and of the same kind of glass, to a temperature of about 280° for several days in the same vapour-bath, under the following conditions:-The therm meters were all placed in glass tubes closed at the bottom. ( being suspended from above), and the tubes were heated by the vapour of boiling bromonaphthalene. One of the tubes-th containing thermonieter C-was exhausted so as to reduce : the air. external pressure on the bulb to zero; the others were open to In thermometer A there was a vacuum over the mercury, but air was admitted into B and C to increase the internal pressure. Consequently, the bulb of A was exposed

a resultant external pressure equal to the difference between the barometric pressure and that of the column of mercury in the stem of the thermometer; the internal and external pressures ut the bulb of B were approximately equal; lastly, the intern pressure on the bulb of C was the sum of the pressures of the column of mercury in the stem and of the air above it, while the external pressure was zero.

The following results were obtained :

Zero before heating...

After 2 hours' heating

After an additional 5 hours' The spines themheating

selves are parti-coloured, the greater part being tinged with a vivid yellow; the tip is blackish-brown. I was unable to extract this pigment with chloroform, or with absolute alcohol even when heated; like so many other colouring substances which are insoluble in these fluids, the pigment could be extracted by potash or ammonia; I found also that tap water, warm or cold, dissolved out the yellow colour; the action was slower than when the water was first rendered alkaline by the addition of ammonia, but, unlike the touraco, the pigment was nearly, if not quite, as completely dissolved. The skin, from which the spines were taken, was a dried skin of an animal recently living in the Zoological Society's Gardens; it had not been preserved in alcohol or treated in any way which might lead to the supposition that the pigment was chemically altered. There is,

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Total rise of zero-point... The thermometers were heated until 5 p.m. each day, the zero-points read on the following morning.

If the diminution of volume of the thermometer buli, usually observed, were due to external pressure, the zero point of 1 should have risen, that of B should have remained nestl stationary, while that of C should have fallen. Instead of sho however, the zero-points of all three thermometers rose at near the same rate; therefore the yielding of the bulbs to pres owing to the plasticity of the glass, if it occurred at all, had sensible effect on the result. SYDNEY YOUNG University College, Bristol, December 12.

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