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as the foundation of that side of medical and surgical practice which is based on a sound knowledge of regional anatomy. The incomplete recognition of the physiological aspect of anatomy is, we think, the weak part of the book, and it is especially shown in the scanty notice which is taken of the action of the muscles and their association with the movements of the joints.

To enable both these lines of anatomical study to be pursued, the student is accustomed to employ at least two text-books; the one in connection with his systematic work, the other as a guide to the dissection of the body. Prof. Macalister apparently expects, as, indeed, he states in his preface, that his text-book should stand in the place of the two customarily employed. We doubt, however, whether this expectation will be fulfilled. For his text-book, in addition to what is essential in topographical description, by containing an account of the microscopic structure of tissues and organs, a section on embryology, and a detailed description of the bones, is necessarily a work of considerable size and weight, and too cumbersome to be conveniently carried to and fro by the student, as is required with a dissecting-room manual. On the whole, therefore, we prefer the old and well-accustomed lines on which text-books have for so long been written, to Prof. Macalister's modified plan.

But whilst expressing our inability to regard the method which has been followed in the descriptive anatomy of the soft parts as an improvement on the customary arrangement of systematic text-books, we recognize with pleasure the clearness of the descriptions and the many suggestive hints, both morphological and practical, which the book contains. The volume is profusely illustrated with upwards of eight hundred wood-cuts, about one half of which are original figures.

OUR BOOK SHELF.

A Treatise on Ordinary and Partial Differential Equations. By W. W. Johnson. (London: Macmillan, 1889.)

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WE have read Prof. Woolsey Johnson's work with some interest: his style is clear, and the worked-out examples well adapted to elucidate the points the writer wishes to bring out. He appears to recognize Boole, but, so far as the text is concerned, does not acknowledge the existence of Mr. Forsyth's fine work. We do not say that he was under any obligation to do so, but nowadays we are so accustomed to see a list of authors upon whom a writer has drawn that we missed it here. An amount of space somewhat greater than usual has been devoted to the geometrical illustrations which arise when the variables are regarded as the rectangular co-ordinates of a point. This has been done in the belief that the conceptions peculiar to the subject are more readily grasped when embodied in their geometric representations. In this connection the subject of singular solutions of ordinary differential equations, and the conception of the characteristic in partial differential equations may be particularly mentioned." This is certainly the most prominent feature of the early chapters, and it is, to our mind, clearly put before the student. Reference is duly made to Prof. Cayley's work in the Messenger of Mathematics (vol. ii.), which initiated the present mode of treatment of the subject, but not to Dr. Glaisher's "Illustrative Examples' (vol. xii.), nor to Prof. M. J. M. Hill's paper (London Math. Soc. Proc., vol. xix.), in which the theorems stated by Prof. Cayley are proved. This paper, though read before the Society, June 14, 1888, may not have reached

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the author before his work was in the printer's hands. ve do not say that a perusal of it would have called for a: further notice than a reference. Symbolic methods cout author satisfies himself with referring the student to the in for their due meed of recognition and employment. The table of contents for the topics included and the orde pursued in treating them. The work consists of twelve chapters divided up into twenty-four sections: i. (1) cusses the nature and meaning of a differential equation between two variables; ii. (2, 3, 4,) equations of the his order and degree; iii. equations of the first order, but not of the first degree, (5) singular solutions (discriminazz cusp-, tac-, and node-loci), (6) Clairaut's equation, geometrical applications, orthogonal trajectories; iv. equations of the second order; v. (9, 10) linear equations with constant coefficients, in (10) symbolic methods art employed; vi. (11-13) linear equations with variable coefficients; vii. (14, 15) solutions in series; viii. (16. the hypergeometric series; ix. (17) special forms of differentia. equations, as Riccati's equation (due reference is made to Dr. Glaisher's classical paper in the Phil. Trans. for 1851. Bessel's equation, and Legendre's equation (reference # made to text-books and memoirs); x. (18-20) equation ential equations of the first order; xii. (23, 24) partial der involving more than two variables; xi. (21, 22) partial d ential equations of higher order. Examples for practice added at the end of each section. Though Prof. Johr== cannot lay claim to have made here any additions to ou knowledge of the subject, he has produced an exceed introductory hand-book for students, and this, we expert. was the object he proposed to himself in its compilatica We have omitted to state that all use of the compit variable is eschewed.

The Land of an African Sultan: Travels in More 1887, 1888, and 1889. By Walter B. Harris, F.R.GS (London: Sampson Low and Co., 1889.)

A GOOD deal has been written about Morocco late. and Mr. Harris's volume is an interesting, although not a very important, contribution to the literature of the subies. He describes first a journey through northern Moroc then a journey with H.B.M. Special Mission to the court of the Sultan at Morocco city, next a visit to Waran and a ride to Sheshuan; and in a final chapter he sums up the impressions produced upon him by the Moors and ther country. In the chapter on his ride to Sheshuan, he describes a place which had been "only once before looked to have produced an exhaustive work on Morocco; bu: upon by Christian eyes." Mr. Harris does not pretend he presents clearly what he himself has had opportunities of observing.

Wayside Sketches. By F. Edward Hulme, F.L.S., F.S.L (London: Society for Promoting Christian Knowledge. 1889.)

THIS is a pleasantly conversational book on all sorts of subjects more or less connected with natural history or country life: birds, caterpillars, flowers, snow-crystals and the forms of clouds, all come in for a share of atten tion. Without having any scientific pretensions of own, the book may well serve to rouse a first interest in many branches of science. The numerous illustrations are very good indeed.

LETTERS TO THE EDITOR. [The Editor does not hold himself responsible for opinion: pressed by his correspondents. Neither can he undertan to return, or to correspond with the writers of retu manuscripts intended for this or any other part of NATULE No notice is taken of anonymous communications.] Influenza.

THE following paragraph, taken from Sir David Brewster's "Life of Sir Isaac Newton," is not uninteresting at the presti time:

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which he has shown that the malady with which he was afflicted September 1693 was probably influenza or epidemic catarrhal fever, which prevailed in England, Ireland, France, Holland, and Flanders in the four last months of 1693. This distemper, which lasted from eight or ten days to a month, was so general, That few or none escaped from it '; and it is therefore probable, as D:. Dowson believes, that Newton's mental disorder was merely the delirium which frequently accompanies a severe attack of influenza. See Dr. Theophilus Thomson's Annals of Influenza or Epidemic Catarrh in Great Britain,' published in 1852 by the Sydenham Society. See also the Philosophical Transactions for 1694, vol. xviii. pp. 105-115." W. GREATHeed.

ABOUT forty-five years ago I paid a visit with a friend to the laboratory of the celebrated chemist Prof. Schonbein, the discoverer of ozone in the atmosphere and the cause of influenza. Just prior to our visit the Professor had obtained some ozone, and had inhaled it for the purpose, as he said, of giving himself influenza, in order to ascertain how it would affect him. We toth distinctly observed most of the ordinary symptoms of the malady. AUGUSTUS HARVEY.

12 Landridge Road, Fulham, January 17.

Rainbow due to Sunlight reflected from the Sea. I HAVE never heard of a rainbow, due to the image of the sun in water, having been seen; and I think the following letter, from an old student of mine of sixteen years ago, may interest your readers. WILLIAM THOMSON.

The University, Glasgow, January 7.

ON September 18, 1889, I saw a rainbow, caused, not by the direet rays of the sun, but by their reflection from the sea.

We were at the height of 900 feet; the sky was all clouded except along the western horizon; the sun, an hour before setting, was hidden; but its rays were reflected from the sea. A drizzle was falling, and my companion was remarking how strong the light from the sea was, when it occurred to me that it might give a bow. And there it was behind us--not the usual recumhent bow, less than a semicircle, but an overhanging one, greater tan a semicircle. The clouds were drifting from the west, so that the sun came into view; and the usual rainbow became visible with its secondary bow; so that three rainbows were seen

ce. The sea-bow and the usual bow were identical at the horizon. The angle between them was greater than the sun's

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angular height, but not double. It seemed as if the complementary segment of the rim had been folded up from beneath into view, but that the colours were not reversed. The sea-bow was just as bright as the secondary bow, which it intersected.

From the fact that the three were seen together, for over 3 minutes, at least in part, I would argue that it is no unusual sight, and that in Scotland, where bows are so frequent, and plenty of comparatively smooth water available, this sea-bow may be looked for and seen.

I may mention, also, that I saw a fourth bow that evening. After the sun had set, a bow of one colour, an orange-pink, took the place of the usual bow. The source of light, I thought, was a cloud just over the place where the sun had set.

WILLIAM SCOULLER.

86 Calle de la Independencia, Valparaiso, November 9, 1889.

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It may be useful for R. L. and some others to apprehend this principle in word-building-viz. that compound Greek adjectives do not take the lengthened genitive as root; thus the correct Latin equivalent for the corresponding Greek adjective is not echinodermatus" but "echinodermus,' not "distomatus" but "distomus." Hence, the correct form for the neuter plural of the former is "Echinoderma ;" and for the neuter singular of the latter is Distomum. And it would be wrong to write "Distomatida" as the family name, and correct to write "Distomidæ." Hence Osteolepidæ and the like are admissible, since they may be considered as formed from adjectives, and not from the substantive (of questionable form itself) in -is.

Exact Thermometry.

R. L. + E.

SINCE the publication of my letter in NATURE (December 19, 1889, p. 152) on the cause of the rise of the zero-point of a thermometer when exposed for a considerable time to a high temperature, two letters on the same subject have appeared, one from Mr. Herbert Tomlinson (January 2, p. 198), the other from Prof. E. J. Mills (January 9, p. 227), who replies to my objections to the plastic theory.

Mr. Tomlinson considers that my experiments seem to leave no doubt that compression, due to the plasticity of the glass, is not the main cause of the rise of the zero-point, but he considers that it is not merely the prolonged heating, but also the change of temperature (heating or cooling), that is effective in bringing about the change. I have not yet had time to make any special experiments to test this point, but I may perhaps mention that such data as I possess seem rather to point to the conclusion that long-continued steady heating is more effective than alternate heating or cooling. As the following experiment, made about a year ago, seems to bear on the point, I give the results :Approximate 6 3 6 6 6 31 66 time in hours. Rise of zero

point

1°·6 0°·15 0°·85 0°′5 0°′1 1°′2 0° 0°

Total

rise of

zero

|

4°4

Two other thermometers, heated each day for about six hours, showed after nine days rises of zero-point of 3°8 and 4°1 respectively, but in these cases the change was apparently not quite complete. The temperature was in each case 280°, and all these thermometers belonged to the same batch as those employed in my experiments already described in NATURE.

Prof. Mills does not regard the experiments as conclusive, but criticizes my results in the following words: "The zero movement, however, only ranged from 1° to 12-small readings which might very possibly have been obtained, or not, on either of the thermometers at other times." This criticism, in striking contrast to the rest of the letter, appears to be rather unkind either to me or to my thermometers, I hardly know which. I sincerely hope that none of my thermometers are capable of such erratic behaviour as to show changes of zero-point of 1° (or even twice this amount if the plastic theory is correct) without extraordinary treatment, or that my readings of temperature are reliable only to within 1° or so. But to make the matter more certain, I will continue the heating of the two thermometers, A and C, under the same conditions as before, and will also heat two more thermometers under similar conditions to about 360°. Prof. Mills mentions the very curious behaviour of lead-glass thermometers at different temperatures, but his objection on that score to the temperature 280° does not seem to apply, as my thermometers are all made of soft German soda-glass. It may, however, be useful to heat two more thermometers to a temperature of about 220° in order to compare the total rise with that at 280° and 360°.

With regard to the statement that the final state of a thermometer kept at the ordinary temperature for an infinite time would differ from that of the same thermometer after being subjected to prolonged heating at a high temperature, I am not prepared to give a decided opinion either one way or the other, but it does appear to me to be rather a daring procedure to make observations of the minute changes of zero-point over a few years, and to extrapolate from a decade or so to eternity.

I am also quite willing to admit that there may be other causes tending to raise the zero-point besides the equalization of tension, such, for instance, as the chemical changes alluded to by Prof. Mills; but I should like to ask, as I am ignorant on the point, whether there is any experimental evidence of their nature or existence. SYDNEY YOUNG.

University College, Bristol, January 11.

Foreign Substances attached to Crabs.

IN your issue of December 26, and also in exhibiting his collection of crabs before the Linnean Society, Mr. Pascoe cast some doubt on the function of the two pairs of modified legs of Dromia vulgaris, which are usually supposed to be adapted to the retention of the sponge with which it covers its carapace.

That these legs were really used for this purpose I was enabled to observe, during my stay at the zoological station in Naples last winter. I had in my tank several specimens, in some of which the sponge had also extended on to the ventral surface, over the edge of the carapace, thus securing a firm hold apart from the action of the legs. In all specimens, however, there are seen, when the sponge is removed, which requires considerable force, two oblique depressions into which the legs fit, giving them thus a distinct hold on the sponge.

If the latter be, however, removed from the animal but left in the tank, the crab soon sets to work to regain possession of its covering, and can be seen to use its modified hinder pairs of legs most effectually for this purpose. It would seem therefore beyond doubt that these modified legs serve not only for holding on the sponge, but also for getting hold of a new sponge, should the old one get injured or die, as must happen not unfrequently. F. ERNEST WEISS. The Zoological Laboratory, University College, January 6.

Galls.

I AM Sorry if I unintentionally misrepresented the opinions of Prof. Romanes and Dr. St. George Mivart in suggesting that they wished to assail the theory of natural selection in their recent communications to NATURE on this subject. They must, however, pardon me for saying that I still think the extract to which I alluded in my note admits this interpretation. As my views of the relations of gall-formation to the theory of natural selection are clearly at variance with those of your correspondents, perhaps you will allow me space to give briefly the grounds upon which I base my conclusions.

There are in England about ninety well-known varieties of galls, and of this number fully a third are found in the oak. About half the oak galls are formed on growing leaves. In nearly one-third of the total number the grub is hatched, and the gall is fashioned in a developing bud. We can readily imagine, in the case of a tree with deciduous leaves, that the presence of a few galls upon its foliage would not greatly affect its chances of survival, if its fitness was in other respects complete. It is otherwise when a gall occupies the position of a developing bud, especially when the bad is a terminal one. In this case there occurs coincidently with, and as a result probably of, the adventitious formation, an arrest of normal development and growth. Indeed, I believe "the gnarled and twisted oak" owes many of its gnarls and most of the twists to the common oak-apple and other bud-galls. If a tree endowed with less developmental vigour and with fewer supplementary buds than the oak had been exposed to the repeated attacks of the insects for many generations in a struggle for existence, it would doubtless have long ago succumbed, and it would have done so by a process of natural selection operating in the ordinary manner, and not "at the end of a long lever of the wrong kind," whatever that may mean. This selective process in the case of gallbearing trees has left possible traces of its action to-day, for I am unaware that any other English tree than the oak is attacked by terminal bud-galls. The terminal leaf-galls of certain Salices and Conifers can scarcely affect their growth and development to the same extent as the bud-galls.

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involuntary host of Dr. Lewis's Filaria, and his leg the seat or Elephantiasis lymphangiectodes, accompanied by hypertrophy of many integumentary structures of the limb. Oak-spangies on the other hand, are to my mind comparable to the circl nests of ringworm, or to the sprouting epithelium of a Verr. necrogenetica. Such comparisons may be of little scient value, yet I take it they are as useful in their place as attenŢA: to gauge the amount of "disinterestedness" shown by a calita when it becomes the unwilling host of the gall-producing Ceuthorhynchus sulcicollis. W. AINSLIE HOLLIS.

Brighton, December 30, 1889.

The Evolution of Sex.

THE interesting note of Mr. M. S. Pembrey in your issue of January 2 (p. 199), induces me to draw the attention of your correspondent to a short paper of mine just published or mo course of publication) in the Ibis, where I communicated b experiences of a friend, who had hatched a series of part eggs, belonging to the genus Eclectus, in which the young males are green, the young females red. It is remarkable t by far the larger number of the birds hatched were males. I: each case only two eggs were laid, and the breeder himself, with out being able to tell why, is of opinion that nearly all t hatches consisted of male birds. As there are still many embry of those Eclectus in my hands, the sex of which is not yet termined, I hope to be able to make known the result of my s vestigation later, whether the pairs are always males, or alway females, or consist of a male and a female bird, at least sometimes Meanwhile, I should be glad to hear if anything more is km.45 about the sexes of birds which lay only two eggs at a time, A. B. MEYEÄ. Royal Zoological Museum, Dresden, January 5.

"Manures and their Uses."

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ALLOW me to thank the well-known writer "W." for h review of the above-mentioned book. "W." does not hold with the view that "farmyard manure is erroneously supper to contain all the necessary plant-foods required for the growth of plants." I believe, with M. Ville and others, that “he farmer who uses nothing but farmyard manure exhausts b land." "W." speaks of this as an "obvious fallacy." If statement is wrong, would "W." kindly answer the quotatio given on p. 76 of the book in question. The quotation "run as follows:

"M. Grandeau (the French agricultural authority) recently estimated that one year's crop in France represents 298.200 tons of phosphoric acid, of which only 151,200 tons were to covered from the stable dung, thus leaving a deficit of 147,000 tons, equal to over one million tons of superphosphate, to t made good by other means.

"M. Grandeau also estimated that the entire number of fir animals in France in 1882, representing a live weight 6,240,430 tons, had accumulated from their food 193.453 tons of mineral matter containing 76,820 tons of phosphoric a These figures give some idea of the enormous quantities of phot phoric acid required to restore to the soil what is continua being carried away by the crops sold off the farm."

It must be borne in mind that in the above estimates, M. Grandeau includes the purchase of oil-cakes and other feeding stuffs. Therefore, if farmyard manure only contains about ha the amount of phosphoric acid (to say nothing of nitrogen, potash, &c.) required to retain the land in a fertile conditio how can I have attached "too much prominence to chemica manures, and too little importance to stock-feeding as a mann agency"? A. B. GRIFFITES

[DR. GRIFFITHS assumes that because, as asserted by M Grandeau, the balance of fertilizing matter in France is agai the land, "the farmer who uses nothing but farmyard mana exhausts his land." This is arguing from general principles special cases, and there is no sequence in his reasoning. A nation may be rushing to ruin, but that does not prevent at t dividual from growing rich. Phosphates and nitrates may diminishing, but that does not prevent them from accumulat o any particular farm. We traverse Dr. Griffiths's stateme without qualification, that the farmer who uses nothing else farmyard manure exhausts his land. We believe he improve his land.-THE REVIEWER.]

MAGNETISM II.

WHE WHEN one considers that the magnetic property is peculiar to three substances that it is easily destroyed by the admixture of some foreign body, as manganese-one would naturally expect that its existence would depend also on the temperature of the body. This is found to be the case. It has long been known that iron remains magnetic to a red heat, and that then it somewhat suddenly ceases to be magnetic, and remains at a higher temperature non-magnetic. It has long been known that the same thing happens with cobalt, the temperature of change, however, being higher; and with nickel, the temperature being lower. The magnetic characteristics of iron at a high temperature are interesting. Let us return to our ring, and let us suppose that the coils are insulated with a refractory material, such as asbestos paper, and that the ring is made of the best soft iron. We are now in a position to heat the ring to a high temperature, and to experiment upon it at high temperatures in exactly the same way as before. The temperature can be approximately determined by the resistance of one of the copper coils. Suppose, first, that the current in the primary circuit which we use for magnetizing the ring is small; that from time to time, as the ring is heated and the temperature rises, an experiment is made by reversing the current in the primary circuit, and observing the deflection of the galvanometer needle. At the ordinary temperature of the air the deflection is comparatively small; as the temperature increases the deflection also increases, but slowly at first; when the temperature, however, reaches something like 600° C., the galvanometer deflection begins very rapidly to increase, until, with a temperature of 770 C., it attains a value of no less than 11,000 times as great as the deflection would be if the ring had been made of glass or copper, and the same exciting current had been used. Of course, a direct comparison of 11,000 to I cannot be made to make it, we must introduce resistance into the secondary circuit when the iron is used; and we must, in fact, make use of larger currents when copper is used. However, the ratio of the induction in the case of iron to that in the case of copper, at 770° C., for small forces is no less than 11,000 to 1. Now mark what happens. The temperature rises another 15 C. the deflection of the needle suddenly drops to a value which we must regard as infinitesimal in comparison to that which it had at a temperature of 770° C.; in fact, at the higher temperature of 785° C. the deflection of the galvanometer with iron is to that with copper in a ratio not exceeding that of 114 to 1. Here, then, we have a most remarkable fact: at a temperature of 770° C. the magnetization of iron 11,000 times as great as that of a non-magnetic substance; at a temperature of 785 C. iron practically non-magnetic. These changes are shown in Fig. & Suppose now that the current in the primary circuit which serves to magnetize the iron had been great instead of very small. In this case we find a very differ

ent order of phenomena. As the temperature rises, the deflection on the galvanometer diminishes very slowly till a high temperature is attained; then the rate of decrease is accelerated until, as the temperature at which the sudden change occurred for small forces is reached, the rate of diminution becomes very rapid indeed, until, finally, the magnetism of the iron disappears at the same time as for small forces. Instead of following the magnetization with constant forces for varying temperatures, we may trace the curve of magnetization for varying forces with any temperature we please. Such curves are given in Diagrams 9 and 10. In the one diagram, for the purpose of bringing out different points in the curve, the scale of abscissæ is 20 times as great as in the other. You will observe that the effect of rise of temperature is to diminish the maximum magnetization of which the body is capable, slowly at

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Inaugural Address delivered before the Institution of Electrical Enineers, on Thursday, January 9. by J. Hopkinson, M.A., D.Sc., F.R.S., President. Continued from p. 254

FIG. 8.

first, and rapidly at the end. It is also very greatly to diminish the coercive force, and to increase the facility with which the body is magnetized. To give an idea of the magnetizing forces in question, the force for Fig. 8 was o'3; and as you see from Figs. 9 and 10, the force ranges as high as 60. Now the earth's force in these latitudes is 043, and the horizontal component of the earth's force is o'18. In the field of a dynamo machine the force is often more than 7000. In addition to the general characteristics of the curve of magnetization, a very interesting, and, as I take it, a very important, fact comes out. I have already stated that if the ring be submitted to a great current in one direction, which current is afterwards gradually reduced to zero, the ring is not in its non-magnetic condition, but that it is, in fact, strongly magnetized. Suppose now we heat the ring, whilst under the influence of a strong magnetizing current, beyond the critical temperature at which it ceases to have any magnetic properties, and that then we reduce the current to

zero, we may in this state try any experiment we please. Reversing the current on the ring, we shall find that it is in all cases non-magnetic. Suppose next that we allow the ring to cool without any current in the primary, when cold we find that the ring is magnetized; in fact, it has a distinct recollection of what had been done to it before it was heated to the temperature at which it ceased to be magnetic. When steel is tried in the same way with varying temperatures, a similar sequence of phenomena

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cent. of nickel is non-magnetic as it is sure to come from the manufacturer; that is to say, a substance compounded of two magnetic bodies is non-magnetic. Cool it, however, a little below freezing, and its properties change: it becomes very decidedly magnetic. This is perhaps not so very remarkable: the nickel steel has a low critical temperature-lower than we have observed in any other magnetizable body. But if now the cooled material be allowed to return to the ordinary temperature it is mag

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FIG. 11.

is observed; but for small forces the permeability rises to a lower maximum, and its rise is less rapid. The critical temperature at which magnetism disappears changes rapidly with the composition of the steel. For very soft charcoal iron wire the critical temperature is as high as 880° C.; for hard Whitworth steel it is 690° C.

The properties of an alloy of manganese and iron are curious. More curious are those of an alloy of nickel and iron. The alloy of nickel and iron containing 25 per

netic; if it be heated it is still magnetic, and remains magnetic till a temperature of 580° C. is attained, when it very rapidly becomes non-magnetic, exactly as other magnetic bodies do when they pass their critical temperature. Now cool the alloy: it is nonmagnetic, and remains non-magnetic till the temperature has fallen to below freezing. The history of the material is shown in Fig. 11, from which it will be seen that from -20°C. to 580° C. this alloy may exist in either of two states, both quite stable-a magnetic and a non-magnetic-and that the state is determined by whether the alloy has been last cooled to -20° C. or heated to 580° C.

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Sudden changes occur in other properties of iron at this very critical temperature at which its magnetism disappears. For example, take its electrical resistance. On the curve, Fig. 12, is shown the electrical resistance of iron at various temperatures, and also, in blue, the electrical resistance of copper or other pure metal. serve the difference. If the iron is heated, its resistance increases with an accelerating velocity, until, when near the critical temperature, the rate of increase is five times as much as the copper; at the critical temperature the rate suddenly changes, and it assumes a value which, as far as experiments have gone, cannot be said to

differ very materially from a pure metal. The resistance of manganese steel shows no such change; its temperature coefficient constantly has the value of oo012, which it has at the ordinary temperature of the air. The electrical resistance of nickel varies with temperature in an exactly similar manner. Again, Prof. Tait has shown that the thermo-electric properties of iron are very anomalous-that there is a sudden change at or about the temperature at which the metal becomes non-magnetic, and that before this temperature is reached the variations of thermo-electric property are quite different from a nonmagnetic metal.

Prof. Tomlinson has investigated how many other properties of iron depend upon the temperature. But the most significant phenomenon is that indicated by the property of recalescence. Prof. Barrett, of Dublin, observed that if a wire of hard steel is heated to a very bright redness, and is then allowed to cool, the wire will cool down till it hardly emits any light at all, and that then it suddenly glows out quite bright again, and afterwards finally cools. This phenomenon is observed with

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