July 13, 1893] 



NATURE 



26 ( 



From this table we have the result that the gases fall into 

 four groups, the members of any one group having within the 

 limits of experimental error the same ratio of the specific 

 heals. 

 These groups are — 



I. Methane. 

 II. The three methyl compounds. 



III. Ethane and its derivatives. 



IV. Propane and its derivatives. 



If the members of a group have the same ratio of the specific 

 heats, wd l^now that the ratio of the internal energy absorbed 

 by the molecule to the total energy absorbed, per degree rise of 

 temperature, is the same for all. Hence we have the result 

 that, with the single exception of marsh gas, the compounds 

 with similar formulae have the same energy-absorbing power, a 

 result which supplies a link of a kind much needed to connect 

 the graphic formula of a gas with the dynamical properties of its 

 molecules. 



From the conclusion we have reached, it follows with a high 

 degree of probability that the atoms which can be interchanged 

 without effect on the ratio of the specific heats have themselves 

 the same energy-absorbing power, their mass and other special 

 peculiarities being of no consequence. Further, the anomalous 

 behaviour of methane confirms what was clear from previous 

 determinations, namely, that the number of atoms in the mole- 

 cule is not in itself sufficieut to fix the distribution of energy, 

 and suggests that perhaps the configuration is the sole deter- 

 mining cause. 



If this is so, it follows that ethane and propane have the same 

 configuration as their monohalogen derivative?, but that 

 methane differs from the methyl compound*, a conclusion that 

 in no way conflicts with the symmetry of the graphic formal.Te 

 of methane and its derivatives, for this is a symmetry of 

 reactions, not of form. 



"On Interference Phenomena in Electric Waves passing 

 through different Thicknesses of Electrolyte." By G. Udny 

 Yule. Communicated by Prof. G. Carey Foster, F. R.S. 



In the spring of 1889 Prof. J. J. Thomson published ' a 

 description of some experiments made by him for comparing the 

 resistances of electrolytes to the passage of very rapidly alternat- 

 ing currents, the method consisting in comparing the thicknesses 

 of layers of different electrolyte; which were equally opaque to 

 Hertzian radiation. Daring last winter I made trial of an 

 arrangement identical in principle but more completely analo- 

 gous to Hughes' induction balance. The method seemed, how- 

 ever, to offer several difficulties and disadvantages, and finally I 

 adopted another, also, one may say, analogous to Prof. Thom- 

 son's, inasmuch as it measures transparencies, but in outward 

 appearance completely different from his. 



The wires B, F, D, about I mm. diameter, were spanned 

 6 cm. apart. If these wires be made too short, a wave-train 

 emitted from B, B' may reach the electrolyte .r,, or the bridge D, 

 be reflected, and return to B before the primary has practically 

 done oscillating. If this occur, the state of the secondary may 

 affect the primary as in an alternate current transformer. If, 

 however, B.r, be made longer than half the effective length of 

 the wave-train, the reflected waves will not reach B until 

 the primary oscillations have practically come to rest, and 

 under these circumstances the latter will know nothing about 

 any alternations in the secondary at or beyond x^. This reaction 

 of the secondary on the primary had been first noticed, and to 

 a serious extent, by Herr J. Ritter von Geitler' with an exciter 

 of the type used by Blondlot.^ 



In the actual apparatus the wires were at Fj run out through 

 a window in a loop of about 50 m. circumference round the 

 laboratory garden. They re-entered the room at Fj and were then 

 run vertically through the vessel for containing the electrolyte. 

 The circuit was completed by another loop, FjFj, 50 m. long, 

 round the garden, re-entering the room at K4, connecting to the 

 electrometer at E, and bridged at D, 2 '25 m. = i A. from the 

 electrometer. According to the researches of Bjerknes {loc. cit.) 

 these dimensions should be sufficient, with the present apparatus, 

 to prevent any sensible reaction. 



The electrometer was the same one as that used by Bjerknes 

 in his researches in the same laboratory. It is a simple quad- 

 rant electrometer with only one pair of quadrants and an un- 

 charged aluminium needle of the usual shape suspended by a 

 quartz fibre. One quadrant is connected to each wire. The 

 needle taking no account of sign, elongations are simply pro- 

 portional to the time integral of the energy : first throws, not 

 steady deflections, are read. 



Various glass jars were used for holding the electrolyte. 

 The wires were run vertically through holes drilled in the 

 bottom of the jar, into which they were cemented. 



Several trials were made of this apparatus with dilute solutions 

 of copper sulphate. Readings were taken in pairs alternately, 

 with no solution in the jar and with some given thickness ; 

 usually about ten readings at each point. The ratio of the trans- 

 mitted intensities so obtained was determined for several points 

 and plotted as a curve. Some 5 or 6 cm. of electrolyte was the 

 maximum thickness that could be used in these first experiments. 

 The curves so obtained for these badly-conducting solutions 

 always differed sensibly from the log-arithmic, and the more 

 so the more the solution was diluted. If the mean log. dec. 

 over the w hole thickness was taken, the corresponding value of 

 the specific conductivity appeared extremely high. 



It appeared likely that these irregularities might be due to 

 interference effects analogous to Newton's rings (by transmission), 

 or the phenomena of " thin plates," particularly in view of the 



f>' 



^-^~U 



^ 'J 



'■^* 



Fig. 



3D 



Let ASA' be a Hertz exciter, and B, B' secondary conductors 

 similar to the primary from which a pair of long wires, stretched 

 parallel to each other, are led off to a considerable distance. 

 One may regard the wires simply as guides for the radiation, 

 which then travels straight up the space between them. If we 

 run these wires for a certain length, /, through an electrolyte, 

 the radiation will have to traverse this and will be partly ab- 

 sorbed. If an electrometer be connected at E, a quarter wave- 

 length from the bridge at the end of the wires, readings taken 

 with various thicknesses of electrolyte should, according to my 

 expectations, give a logarithmic curve, from which the specific 

 resistance would be at once calculable. 



The actual dimensions of the exciter, &c., erected were the 

 same as those use by Bjerknes. ^ 



A, A', B, B' circular zinc plates, diameter . 40 cm. 



Distance from A to B 30 „ 



Length of wire ASA (2 mm. diameter) . . 200 ,, 



Wave length, A 900 ,, 



" Roy. Soc. Proc," vol. xlv. p. 269, i88g 

 IVieiientann's Annalen, vol. xliv. p. 513, 



[891. 



NO. 1237, VOL. 48] 



results obtained just previously by Mr. E. H. Barton in the same 

 laboratory. I consequently desired to investigate forsuch inter- 

 ference phenomena over as great a thickness of electrolyte as 

 the absorption would permit of using. Distilled water offered 

 itself naturally as the best electrolyte for this purpose. 



For the containing vessel a glass cylinder 114 cm. high was 

 used ; the internal diameter varied somewhat, but was about 1 2 

 cm. at the narrowest. 



With this apparatus a series of observations were made for 

 various thicknesses of distilled water. To cover, as far as possible, 

 irregularities in sparking, readings were now taken in pairs 

 alternately at the point to be determined and some other point 

 taken for the time as the standard ; it would have caused ton 

 great delay, and consequent irregularity in the effectiveness of 

 the sparks, were all the water to be siphoned out between each 

 pair of readings. As before, ten or twelve readings were usually 

 taken at each point. The throw obtained with no liquid was 

 also always taken as unity. 



As a specimen of the usual spark variation', the following 



1 Doctor-Dissertation, Bonti, Jan. 1893, p. 32. 



2 Com/t. Rend., vol. cxiv., p. 283, Feb. 1892. 



