Intelligence and Miscellaneous Articles. 393 



this way the phenomenon seems likely to prove of value in the sepa- 

 ration of organic compounds. The phenomena sometimes also afford 

 curious evidence of chemical combinations ; but this subject cannot 

 here be further dwelt upon. 



The appearance which the rays from an electric spark produce in 

 a solution of sulphate of quinine, shows that the spark is very rich 

 in invisible rays of excessively high refrangibility, such as would 

 plainly put them far beyond the limits of the maps which have 

 hitherto been made of the fixed lines in the chemical part of the 

 solar spectrum. These rays are stopped by glass, but transmitted 

 through quartz. These circumstauces I'ender it probable that the 

 phosphorogenic rays of an electric spark are nothing more than rays 

 of the same nature as those of light, but which are invisible, and not 

 only so, but of excessively high refrangibility. If so, they ought to 

 be stopped by a very small quantity of a substance known to absorb 

 those rays with great energy. Accordingly the author found that 

 while the rays from an electric spark, which excite the phosphores- 

 cence of Canton's phosphorus, pass freely through water and quartz, 

 they are stopped on adding to the water an excessively small quan- 

 tity of sulphate of quinine. 



At the end of the paper the author explains what he conceives 

 to be the cause of the change of refrangibility, and enters into some 

 speculations to account for the law according to which the refrangi- 

 bility of light is always lowered in the process of internal dispersion. 



LXII. Intelligence and Miscellaneous Articles. 



REMAEKS ON THE MECHANICAL EQUIVALENT OF HEAT. 

 BY A. r. KUPFFER. 



WHEN a perpendicular wire fastened at its upper end is loaded at 

 its lower end with a weight, it is expanded longitudinally to a 

 certain degree. Let us, for example, imagine a wire whose length 

 and radius (I assume that the section is a circle) are equal to unity 

 stretched by the unity of weight, and call the extension which it 

 thus suffers Z ; we will call this quantity the elastic constant. 



When the same wire has its temperature raised from the freezing 

 to the boiling-point of water, it also suffers an expansion, which we 

 will call a. 



The quantity of heat which effects this expansion can only be 

 determined comparatively; we may imagine a cylinder of water, 

 whose height and radius at 32° are likewise equal to unity, and take 

 the quantity of heat necessary to raise the temperature of this cylin- 

 der from 32° to 212° as unity. Then 



m . S 

 is the quantity of heat necessary to raise the temperature of the 

 above-mentioned wire from 32° to 212°, m representing the specific 

 heat of the metal of which the wire is made, and S its specific weight 

 compared with water. 



Now since the extension which a wire suffers is equal to the forces 



