November 14, 1895] 



NA TURE 



47 



no near affinity with any other, either palaeontological or recent. 

 While the structure of the stem resembles that of the Cala/nariea, 

 the mode of formation of the spores is analogous to that of the 

 LycopodiacecE. — On the development of 'I'riiholonia tcrreuiii, by 

 "■ [lor P. Voglino, 



SOCIETIES AND ACADEMIES. 



London. 

 Physical Society, November 8.— Prof. A. W. Riicker, 

 fcVice- President, in the chair. — Mr. W. H., Everett read a paper 

 )n the magnetic field of any cylindrical coil or plane circuit. 

 The method of treatment is based on the formula for the force 

 iue to an element of current. A single integration applied to 

 Sne component of this force gives for any point in the field due 

 plane circuit the force perpendicular to its plane ; and a 

 Jouble integration gives the longitudinal force at any point due 

 a cylindrical coil of any cross-section, the depth of winding 

 jing supposed inconsiderable. For coils in which the latter 

 condition does not hold, an approximate solution can readily be 

 found. The force parallel to the plane of a circuit and the 

 transverse force due to a coil are investigated in a similar 

 manner. The general results are of a very simple form, and 

 Admit of easy approximate calculation. Special formulae are 

 <leduced for coils of rectangular cross-section, the general 

 ■expressions being in this case integrable. Appended to the paper 

 are some numerical results giving the values of the forces 

 At different points due to coils of various dimensions. 

 Prof. Perry said he considered the paper to be a valuable one, 

 particularly as illustrating a practical mathematical method of 

 integrating Mr. Trotter .said the paper was of interest to him, 

 as he considered that several of the author's results might be 

 applied to the solution of problems on illumination — for instance, 

 the illumination of a room by a circle of lamps. Mr. Rhodes 

 regretted that it had not been possible to supply a proof of the 

 paper before the meeting. The method in which the author 

 •obtained the force outside a solenoid as the difference of the 

 forces due to two solenoids, reminded him of the method em- 

 ployed in calculating the attraction of, say, a truncated pyramid. 

 Prof. Silvanus Thompson said the author had mentioned several 

 previous papers on the subject, but had not referred to one by 

 Prof Viriamu Jones, in which the force due to a solenoid is 

 •obtained in terms of elliptic integrals. Another method of 

 attack was to calculate the work done when a 'unit poie is carried 

 through the solenoid and back outside to the starting-point. 

 Prof. Ayrton said he also regretted the absence of a proof of the 

 l^aper. He considered it of great importance to have exact and 

 simple methods of calculating the forces due to a solenoid. The 

 ■Chairman (Prof Riicker) said he had made a somewhat 

 similar calculation in connection with the magnetic effect 

 ■oi sheets of basalt below the surface of the earth. — Mr. E. 

 H. Griffiths read a paper, by himself and Miss Dorothy 

 Marshall, on the latent heat of evaporation of benzene. 

 The method employed is similar to that used by one of the 

 authors in the determination of the latent heat evaporation of 

 water {/V«7. Trans. 1895). The loss of heat due to the evapora- 

 ion is balanced by (a) the heat supplied by an electric current ; 

 {b) a secondary supply due to the work done by the stirrer ; (t) 

 a slight gain or loss due to small unavoidable changes in temper- 

 ature of the calorimeter. The comparative values of the various 

 sources of heat (if we denote the supply due to the electrical 

 -current by 1000) is approximately : — Electrical = 1000 ; stirring 

 = II ; changes in calorimeter temperature ± 5. The electrical 

 supply could be measured with extreme accuracy, and the above 

 table shows that small errors in the determination of the remain- 

 ing thermal quantities are of little importance. The results may 

 ibe summed up in the formula 



L = 107-05 - 0*1981 fl 

 where 6 is the temperature and the thermal unit at 1 5' C. is used. 

 The discussion on this paper was postponed till after the reading 

 of the paper by Prof. Ramsay and Mi.ss Marshall, on a method of 

 ■comparing the heats of evaporation of different liquids at their 

 boiling points. The method employed has already been 

 described before the Society (January 11, 1895). The liquid to 

 be experimented on is put into a glass bulb enclosed in an outer 

 jacket filled with the vapour of the same liquid. An open tube 

 is attached to the top of the bulb, so that there is free communi- 

 cation between the interior and the vapour jacket, 

 and no loss of material. Inside the bulb is a spiral 

 ■of fine platinum wire, attached to stout plati.num 



NO; 1359, VOL. 53] 



terminals which are sealed into the glass. The temperature of 

 the liquid in the bulb is raised to the boiling point by the vapour 

 jacket ; thus when a current is sent through the wire, the whole 

 of the heat developed is spent in converting a portion of the 

 liquid into vapour. Two such bulbs are connected in series, 

 and the ratio of their losses of weight is the inverse ratio of the 

 heats of evaporation of the liquids. A correction is made for the 

 inequality in resistance of the spirals, and the ratio of the dif- 

 ferences of potential between the ends of the spirals, when the 

 current is passing, is determined in each experiment by Poggen- 

 dorfTs method. Results are given for fourteen liquids. Prof. 

 Ramsay drew special attention to the table giving the values 

 of the quotient ML/T, where M is the molecular weight, T the 

 absolute temprature, and L the latent heat. Very curious 

 differences are noticeable in the case of water, alcohol, and acetic 

 acid. Prof. Carey Foster expressed his admiration for the method, 

 since it obviated the necessity of knowing the specific heat of the 

 liquid vapour. Prof. Silvanus Thompson said the difficulty ex- 

 perienced in the case of water due to electrolysis might be 

 obviated by the employment of a spiral of lower resistance and 

 a larger current, so that the difference of potential between the 

 ends of the spiral should be less than 17 volts. The Chairman 

 said Captain Abney had asked him to inquire to what extent 

 the temperature of the liquid was affected by radiation. 

 Mr. J. W. Rodger asked if any direct experiment had been 

 made to determine if the temperature of the liquid was not above 

 its true boiling point. In some cases differences of as much as 

 2° might exist between the temperature of the liquid and that of 

 the vapour given off. The dififerences in the value of ML/T 

 in the case of water, alcohol and acetic acid might be due to the 

 fact that the vapours of alcohol and water were simple, while the 

 vapour of acetic acid was complex. Mr. R. Appleyard sug- 

 gested that the differences obtained i.i the case of water might 

 be due to the presence of dissolved air. Mr. Griffiths said that 

 the objection to the adoption of Prof. Thompson's suggestion 

 was the fear that with short wires an excessive difference in 

 temperature between the wire and the liquid might exist. Mr. 

 Rhodes asked if Mr. Griffiths could trust his determinations of 

 temperature to ^^J^jg^th of a degree. Mr.Griffiths, in reply, said 

 that he thought there was no limit to the accuracy with which a 

 difference of temperance could be measured ; the absolute tem- 

 perature, however, he only relied upon to xAiy'^h of a degree. 

 Prof. Ramsay said the fact of superheating existing would not 

 affisct the results, since near the temperatures at which they were 

 working the latent heat did not vary appreciably with the tem- 

 perature. In reply to Captain Abney, he said some previous 

 experiments by Dr. Young and himself had shown that the 

 vapour jacket was quite impervious to radiant heat from 

 without 



Paris. 



Academy of Sciences, November 4. — M. Marey in the 

 chair. — Action of silicon on iron, chromium, and silver, by M. 

 Henri Moissan. By heating silicon with soft iron, chromium, or 

 silver in the electric furnace or otherwise, compounds havjng the 

 composition Fe.^Si and CrjSi are produced by the two former 

 metals, and silver dissolves a notable proportion of silicon, but 

 deposits it again on solidification in the crystalline state. The 

 silicides of iron and chromium are produced at temperatures 

 below the melting points of either constituent, probably owing to 

 the vapour tension of silicon at the temperature of formation ; 

 the whole process much resembles cementation. These silicides 

 are readily attacked by hydrofluoric acid or aqua regia, slowly 

 acted on by hydrochloric acid and unacted on by nitric acid. 

 Fused potassium nitrate and chlorate do not act on these com- 

 pounds, but they are easily decomposed by fusion with a mixture 

 of nitrate and carbonate. — M. de Freycinet describes the aim of 

 his book, " Es.says on the Philosophy of the Sciences," of which 

 a copy is presented to the Academy. — Elements of Swift's comet 

 (1895 II)' by M. L. Schulhof. These elements are compared 

 with the elements for Lexell's comet given in Le Verrier's table 

 (for /i = + o"9), and show very near agreement. — Spectro- 

 scopic researches on the star Altair. Recognition of an 

 orbital movement 'and of an atmosphere, by M. H. Des 

 landres. (See our Astronomical Column.) On the binomial 

 differential equation of the first order, by M. Michel Petro- 

 vitch. — New method for the extraction of roots of numbers, 

 by M. Manuel- Vazquez Prada. — Expression of the pressure 

 supported by the shaft of a hydraulic turbine at work. 

 Theorem concerning the dynamical effect of the water. Note 

 by M. Bertrand de Fontviolant. It is concluded that : The 



