The form Mycoderma cerevisiae was thoroughly examined. The author's results confirm what is known as to its aërobian characters. Statements as to its identity with Oidium lactis were not only not confirmed, but the author grew these two forms side by side, and maintains their distinctness. Nor could he obtain spores in this fungus, thus failing to confirm earlier statements to the contrary. He regards it as probable that oildrops have been mistaken for spores; he also finds that in later stages of fermentation by this organism a strong oily-smelling body is produced.

66

With regard to Bacterium aceti, the author has nothing new to add. A point of some interest was the repeated production of acetic ether, which scented the laboratory, when this Schizomycete was growing in company with the small white aerobian top-yeast referred to under (8). Full details regarding the rest of the organisms, which have nothing to do with the gingerbeer plant" proper, are given in the original paper. Physical Society, December 4.-Prof. W. E. Ayrton, F.R.S., President, in the chair.-A paper on a permanent magnetic field was read by Mr. W. Hibbert. The author had noticed the approximate constancy of an aged" bar magnet, and he obtained still greater constancy by attaching pole pieces to a bar magnet, of such a shape as to give a nearly closed circuit of small magnetic resistance." The pattern now described consists of a steel rod I inch diameter and about 2 inches long, with a cast-iron disk 4 inches diameter and thick fixed at one end; the other end is fitted in a hemispherical iron shell which surrounds the bar and comes flush with the upper surface of the disk. An annular air space less than inch wide is left between the cylindrical surface of the disk and the inside of the shell, and when the bar is magnetized, a strong magnetic field exists in this space. To use this field for producing electromagnetic impulses, a coil of wire is wound in a shallow groove on a brass tube which can slide axially through the annular space, thus cutting all the lines. The tube is allowed to fall by its own weight, a neat trigger arrangement being provided for effecting its release. The instrument exhibited had 90 turns of

wire in the coil, and the total magnetic flux across the air space was about 30,000 C.G. S. lines. A large electro-magnetic impulse is, therefore, obtainable even through resistances as great as 10,000 ohms. Tests of three instruments show that there has been practically no magnetic decay in seven months. The author therefore considers them satisfactory, and is prepared to supply them as magnetic standards. To facilitate calculation, the number of lines will be adjusted to a convenient number, say 20,000 or 25,000. Several uses to which the instruments are well suited are mentioned in the paper, and a simple way of determining permeability by the magnetometer method is described. Mr. Blakesley thought the name given to the instrument was inappropriate, for it really gave a constant impulsive E. M. F. Dr. Sumpner said the constancy of the sensibility of d'Arsonval galvanometers was a measure of the Constancy of magnets having nearly closed circuits. Such instraments, in use at the Central Institution, had remained unchanged for several years. Prof. S. P. Thompson admired Mr. Hibbert's instrument, and thought it would be very useful in laboratories. Standard cells, he said, were not always reliable, and condensers were the most unsatisfactory of electrical standards. On the subject of permanency of magnets, he said that Strouhal and Barus found that magnets with nearly closed circnts were most constant, and that, to give the best results, the hardness of the steel should be less the more closed the Ciuit. Mr. Hookham had also found that by using a nearly cel circuit, and reducing the strong magnetization by about to per cent., great constancy could be obtained. Some years

ago he (Dr. Thompson) had tried the effect of ill-treatment on ingnets, and observed that touching or hitting a magnet with non-magnetic material had little effect, whilst similar treatment with iron or magnets affected them considerably. Suddenly removing the keeper of a magnet tended to increase the magnetism, whilst putting a keeper on suddenly had the reverse effect. Strouhal and Barus had also investigated the temperature coefficient of magnets, and found that this might be reduced by

subjecting the magnet to rapid changes of temperature after the first magnetization, and then remagnetizing. Mr. W. Watson inquired what was the percentage fall in strength of Mr. Hibbert's magnets. The bars used in magnetic surveys had been tested frequently, and they lost about o'5 per cent. in 6 months. The President asked what were the temperature coefficients of the magnets described in the paper? Mr. Evershed, he said, thought it was between O'OI per cent. and o'05 per cent. for ordinary magnets. He thought the instrument shown by Mr. Hibbert would be of immense value if the magnet was really permanent. By it ballistic galvanometers could be readily calibrated, and, when combined with a resistance box, it could also be used as a standard for current; for, since the constant of a ballistic galvanometer for quantity can be determined from its constant for current, if the periodic time be known, conversely that for current can be found from the constant for quantity. In some instances this would be of great use. Speaking of the temperature coefficient of condensers, he said that in some cases the specific inductive capacity of dielectrics diminished with rise of temperature whilst in others it increased. Mr. Hibbert, in reply, said he found the temperature coefficient of his magnets to be, roughly, about 0'03 per cent., but he had not investigated the matter very carefully. In making his measurements no correction had been made for the variation of capacity of his condenser with temperature.-Mr. Walter Baily took the chair, and the President communicated a note on rotatory currents. The subject, he said, was probably familiar to most persons present, for it had been frequently referred to in the scientific papers. Alternate currents could be obtained from an ordinary direct current dynamo by making contact with two points in the armature, say by connecting these points to insulated rings on the shaft, and using extra brushes. A direct current motor similarly treated transforms direct currents into alternating currents, or into mechanical power. If two pairs of points in the armature be selected, situated at opposite ends of two perpendicular diameters, then two alternating currents differing in phase by 90° can be obtained; and by choosing suitable points in the armature, two, three, or more currents differing in phase by any desired angles can be produced. In ordinary motors the connections for doing this would be troublesome, but the Ayrton and Perry form, which has a stationary armature, lends itself readily to this purpose, for contact can be made with any part of the armature with great facility. A motor of this kind was exhibited, in which contact was made with four equidistant points on the armature. On connecting opposite points through fine platinum wires, and running the motor slowly, the wires glowed alternately, one being bright whilst the other was dark, and vice versa, thus demonstrating the existence of two currents in quadrature. When the four points on the armature were wires became incandescent in succession, the glow appearing to joined to the four corners of a square of platinum wire, the travel round the square, and suggesting the idea of rotatory currents. A Tesla alternating current motor was also driven by two currents differing in phase by 90°, obtained from the armature of the Ayrton and Perry direct current motor above mentioned. The ease with which currents differing in phase by any amount can be obtained from such a motor led the author to investigate theoretically the case of two circuits connecting opposite ends of two diameters inclined at any angle, a. Calling the currents in these circuits at any instant, A1 and A2, he had found that

The expression for p shows that the phase of the current in cir cuit A, is independent of the resistance. On the other hand, varying alters . It was also pointed out that tan (+4) is generally greater than tan a.-Prof. J. Perry, F.R.S., read a paper on struts and tie-rods laterally loaded. He pointed out that, in the case of struts, a slight want of straightness may considerably reduce the breaking load. Even if a strut be originally straight and the thrust properly distributed, its weight usually produces lateral loading and consequent bending. Similarly, centrifugal force produces lateral loading in connecting rods. For some years the author has given his students practical examples of struts and tie-rods to work out, taking into account the effect of lateral loads. The chief results obtained, together with a general treatment of the whole subject, are embodied in the paper. Where the curves of bending moment and the deflections due to lateral loading can be easily developed by Fourier's series, solutions can readily be found. Simple cases of uniformly loaded struts and tie-bars have been fully worked out, and also the case of locomotive coupling rods. In one problem on the latter subject, a rectangular cross-section was chosen, and the proportions of depth to breadth determined so as to make the rod equally strong in the two directions when running at various given speeds. With cranks 12 inches long, the results show that, at a speed of 390 revolutions per minute, the ratio of depth to breadth must be infinite, so as to give equal strength, so great is the influence of the lateral loading due to centrifugal force, when combined with the thrust. Horizontal tie rods loaded by their own weight have been investigated, and the tensions required to neutralize compression due to bending determined. A steel bar, I inch diameter and 48 inches long, was used as a strut, with a thrust of 1500 pounds. The maximum stress, due to bending by its own weight alone, was 810, and on applying the thrust the maximum stress was raised to 23, 190, or about 26 times that due to lateral loading alone. More complex cases have also been treated, the results of which are given in the paper.

PARIS.

Academy of Sciences, December 14.-M. Duchartre in the chair. On the distribution of prime numbers, by M. H. Poincaré. On the fixation of nitrogen by arable soils, by MM. Arm. Gautier and R. Drouin. The conclusion is drawn that only soils containing organic matter fix the free or ammoniacal nitrogen of the atmosphere, even in the absence of plants, and that the organic matter existing in all arable soil is an indispensable intermediary in this fixation of nitrogen.-On the camphoric and isocamphoric esters, and the constitution of the camphoric acids, by M. C. Friedel.-Remarks on the history of supersaturation, by M. Lecoq de Boisbaudran. The author gives some notes, made by him in 1866, on the subject of supersaturation, which are in agreement with the phenomena of solution observed in recent years.-Observations of Borrelly's asteroid (Marseilles, November 27, 1891), made at Paris with the East Tower equatorial, by Mdlle. Klumpke. Observations for position were made on November 30, December 2 and 5.-On integrals of the second degree in problems of mechanics, by M. R. Liouville. On a class of congruences of lines, by M. A. Petot.-On the actual state of geodetic and topographic works in Russia, by General Venukoff.-A brief note on the maps of Russia, prepared under the direction of General Kowersky.-On circular polarization, by M. E. Carvallo.-On a thermo electric standard of electromotive force, by M. Henri Bagard. The author has experimented with thermo-electrolytic couples consisting of two liquids, one an amalgam of zinc, containing a known proportion of this metal, and the other a solution of sulphate of zinc. He finds that such a couple is absolutely constant between two given temperatures, its electromotive force between o° and being given by the formula

E=0001077 + 0·000000902.

And it is not necessary to exercise any great precision in the determination of the weight of zinc dissolved in the known weight of mercury to form the amalgam, for the variation of the electromotive force when the couple is at the temperatures o° and 100° appears to be only 0.0001 volt when the proportion of zinc was varied from 0.00025 to 0.00075 the mass of the mercury.-The three basicities of phosphoric acid, by M. Daniel Berthelot. The basicities have been investigated by the author using a method of determining the electric conductibilities of phosphoric acid solution, and of the same with varying quantities of soda, potash, or ammonia respectively added. The conclusion is drawn that monobasic and bibasic phosphates are stable even in dilute solution, and that the tribasic alkaline phosphates are nearly completely dissociated in dilute solution. Phosphoric acid differs completely from the true tribasic acids as the monobasic and bibasic salts of the latter are partially dissociated by water, and the tribasic salts, on the contrary, are stable in solution.— Salts in solution, sodium sulphate and strontium chloride, by M. A. Etard.-A green solid chromic sulphate, by M. A. Recoura. It has the formula Cr(SO4)3,11H2O. Bismuthic acid, by M. G. André.-On the distillation of oil, by M. Pierre Mahler. A new porcelain, asbestos porcelain, by M. F. Garros.On the presence of reticulated tissue in the muscular walls of the intestines, by M. de Bruyne. On the first phases in the development of Crustacea edriophthalma, by M. Louis Roule.-On Gymnorhynchus reptans, Rud., and its migration, by M. R. Moniez.-On the role of the foot as a prehensile organ in Hindoos, by M. Felix Regnault. Many travellers have remarked on the ability possessed by most Hindoos of using the foot as well as the hand in work of all descriptions. M. Regnault has made some measurements of the lengths of the feet and toes of a number of natives, and draws some conclusions therefrom as to the adaptation "of the organ to the function."--On the discovery of Tertiary shells in the volcanic tufa of Limburg (Grand Duchy of Baden), by M. Bleicher. -The circulation of winds on the surface of the earth: fundamental principles of the new theory, by M. Duponchel.

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CONTENTS.

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169

172

173

Wright: "Principles of Agriculture"

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Dyer and Whitcombe: "Elementary Trigonometry

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analogy, nevertheless theoretical speculations and practical researches are indicated, which, in the long run, must throw more light on the question.

But, in spite of all this, the book is not satisfying. The main objections which have been urged against the physical theory still exist.

To the fundamental question" Is solution a physical or a chemical process?"--the answers are various. The opening definition and much that follows seem quite decisive on this point: "Solutions are homogeneous mixtures."

Dissolved substances obey gaseous laws because "the molecules of the solvent in the interior of the solution act equally in all directions on each molecule of the dissolved substance, these molecules are all free to move as if there were, on the whole, no action upon them. Hence it follows that the kinetic energy of the molecules of the dissolved substance is equal to that of the gas at the same temperature."

The deviations of concentrated solutions from the simple gaseous laws are explained by the fact that in such cases the osmotic pressure is high, and that “compound gases of simple composition show marked deviations from the gaseous laws at such pressures."

The inference from such statements obviously is, that solution is purely physical; to the dissolved substance are to be ascribed even the deviations from the gaseous laws; the solvent may be ignored. This is, indeed, the logical outcome of the physical theory.

On the other hand, evidence such as the following has to be considered :

"Every liquid is capable of taking up every gas, and combining therewith to form a homogeneous liquid or solution. . . Two classes of these gas-solutions are to be distinguished. . . . In cases belonging to the second class, e.g. in a solution of hydrogen chloride in water, we have sufficient grounds to assert that chemical change

occurs."

The distinction drawn between crystalloids and colloids is of the same order as the above :-

"Those of the first group (crystalloids) dissolve in water with more or less marked changes of temperature; they raise the boiling-points, lower the freezing-points, and generally exert a marked influence on the properties, of their solutions. The others (colloids) do not exhibit all these properties: their solutions are mechanical mixtures rather than compounds."

Experiment has shown that the molecular weight of the same dissolved substance, obtained by the Raoult methods, varies in many cases with the solvent. In order to make theory harmonize with practice, this explanation is given :

"We know that iodine, sulphur, and many other substances exist in different molecular conditions. It is not, then, to be wondered at that a definite substance should exhibit different molecular conditions when dissolved in different solvents. The different solvents act like different temperatures or pressures.”

The notion of a passive solvent evidently does not here apply. Even on making allowance for a loose use of the terms mixture and compound, it is hard to see how these latter statements accord with the ideas of the functions of the solvent and dissolved substance derived from those quoted previously.

At

That the book is a portion of a larger treatise is evident, to its detriment, in several ways. One instance, which can hardly escape observation, is the absence of any detailed account of the support to the physical theory which has been drawn from the electrolysis of solutions. first sight, it is difficult to conceive that, in a work on the physical theory, of which the hypothesis of electrolytic dissociation is an integral part, no mention should be made of the quantitative estimate of the degree of dissociation which has been derived from a study of electric conductivity. The reason is, that electro-chemistry is treated in Vol. II. of the "Lehrbuch," and a second edition of this volume is not yet published. It would have been judicious to have delayed publication of this book till portions of the subject of electro-chemistry could have been included.

It would have been desirable, it seems to us, to have made some adequate reference to other theories which have been put forward in explanation of the phenomena of solution. The only statement which can be construed into an allusion to the hydrate theory occurs when treating of the point as to whether or not a salt in aqueous solution is united with its water of crystallization. And here the question is somewhat contemptuously disposed of:

"The endeavours of many investigators to find proofs in favour of the existence in solutions of combined water of crystallization have not led to results which can be received without objection; these endeavours may therefore be passed over."

Fault might well be found on the score of incompleteness with much of the evidence put forward in portions of the book. The chapter on salt solutions is one of the most striking; it is, indeed, the only one which has for its theme the dissociation hypothesis; and bearing in mind the contention which this hypothesis has created, here if anywhere the matter put forward should have been beyond criticism. Tables are given of compressibilities, surface-tensions, viscosities, &c. ; while, to begin with, these properties are not defined, and several necessary details are omitted. Viscosity may be taken as a special and perhaps the worst example. Two tables are given with numerical values for viscosities. Whether these are absolute coefficients in dynes or relative times of transpiration is not stated. They are in reality relative values, the transpiration time of water under the experimental conditions being taken as unity. The numbers in the first table are said to have been "determined with half normal solutions, and referred to equivalent quantities of salt." The meaning of this rather redundant sentence is not quite clear. As a matter of fact, the observations were taken with half normal solutions, and referred to normal solutions by means of Arrhenius's formula connecting viscosity with concentration. Nothing whatever is said about the strength of the solutions used for the observations in the second table. They also relate to normal solutions, and were obtained by a similar but not identical method. The most important omission, however, and one occurring in the case of other properties, is that of the temperature of observation. When it is remembered that at 100° the viscosity coefficient of water is only one-fifth what it is at o°, the influence of temperature on viscosity is apparent. The difficulty in attempting to

compare viscosities has always been the choice of suitable temperatures of comparison-temperatures at which the substances are in comparable conditions. Reference to the original papers shows that the temperature of observation in the examples given was uniformly 25°. Whether under such conditions the viscosities obtained are comparable is open to question, and this point should have been discussed before any stress was put upon the figures, Such details as these ought surely to have been noted as necessary accompaniments of the experimental results.

In other directions the same tendency to omit essential particulars is traceable. In describing the series of operations whereby van 't Hoff was enabled to apply thermodynamics to solutions, it is not shown that the cycle, as conceived by him, is a reversible one. The whole practical utility of the process depends on its reversibility, for then only does the second law of thermodynamics apply. In connection with this point it is not obvious why the translator should prefer the term “reversible cyclical process" to the time-honoured and compact "reversible cycle." The use, too, of the shortened "cyclical process" as the equivalent of " reversible cycle" is inaccurate.

No doubt the incompleteness mentioned is due to the effort made by the author to make the most of his space. In some cases, however, space might be gained. For example, it is surely excessive to give two pages to Voit's method of obtaining diffusion constants, if it led to results which were "quite erroneous"; or to devote three pages to Planck's deduction of the vapour pressure of dilute solutions, if the fundamental thermodynamical equations are assumed.

Several points which require alteration may be summarized here. On p. 7, van der Waals's equation is given wrongly, a bracket being omitted. b in the equation is four times the volume of the molecules, not the volume of the molecules, as stated on pp. 7 and 34. No definite mention is made of what the ordinates and abscissæ are in the diagrams on pp. 66 and 67. On p. 70" differentiating for T❞ would usually be "differentiating with respect to T." "Narrower " should be "wider on p. 97, line 15. The expression 200 grams capacity" is used on p. 118. On p. 136, square root" should be "square." On pp. 186 and 187, 2015 is written for o On p. 237, 1/6 should be 1/7. On p. 238, is given instead of b- Bc 1-C'

66

b-B I-C

Mr. Pattison Muir has evidently attempted to give the sense of the original, without confining himself to a literal translation. He has succeeded in making a readable book, although in one or two instances, as in the account of magnetic rotation, the meaning is slightly obscure.

A careful study of this the latest addition to the literature on solution will, we think, confirm what to many has been all along apparent that solution is in the highest degree a complex process, and that the physical theory errs in treating it as being altogether too simple. Despite the success of this theory, which by establishing a striking analogy has admittedly done much in giving a fresh impetus to investigation, the mechanism of the process is still hidden. The attitude assumed by the upholders of

Colour Blindness and Colour Perception. By F. W. Edridge Green, M.D., F.G.S. (London: Kegan Paul, Trench, Trübner, and Co., 1891.)

Na work with this title one naturally expects to find

that such recognized authorities on the theory of colour perception as Young and Helmholtz are treated with the respect due to their labours and researches. The writer, however, not only refuses to pay homage at the shrine of such masters of natural philosophy, but deliberately devotes a considerable portion of his work to an exposure of the "fallacy of the Young-Helmholtz theory." The preface informs us that the book has been written for the benefit of those who may have to test for colour blindness. To such it will hardly be a recommendation to learn that the theories of Young and Helmholtz are mere fallacies, and that the tests for colour blindness as instituted by Prof. Holmgren are not worthy of the name. The question, of course, arises, What theory are we to adopt relative to colour perception when we have surrendered our allegiance to the theories which Mr. Green denounces? The author answers this query for us by propounding his own doctrine-" an application of the theory of psycho-physical perception, described in my book on 'Memory,' to the phenomena of colour blindness and colour perception." The arguments in support of this theory are based upon the examination of some 116 colour-blind persons, not an over-large number of cases to generalize from, especially when we learn something of the method pursued in the examination. Information afforded by the colour-blind themselves is one of the chief sources of Mr. Green's knowledge respecting colour blindness. He states that he has derived much valuable information from colour-blind persons relating to facts concerning their colour perception. We question much the trustworthiness of data acquired by interviewing colour-blinds as to the phases of their visual infirmity. Yet Mr. Green characterizes this information as trustworthy, and alludes to it as "definite facts of colourblindness, to which any future theory must conform." Many writers on colour blindness have stated that naming colours is a useless and misleading method of examination, because the colour-blind must use the conventional colour names and use them at random. But this reasoning, we are told, is a fallacy, because the colour-blind do not name colours at randɔm, but in accordance with their ideas of colour! Such is the language in which the author disposes of the "fallacy " of Holmgren's wool test. Equally illogical is another of his conclusions: "If, as some persons have said, testing by colour names is useless, then the whole series of colour names is useless."

Prof. Holmgren, it is admitted, has done good service in bringing the subject of colour blindness