200 



violet, and that, not only for these rays as a whole, hut for the rays 

 of each refrangibility in particular. For this purpose it is sufficient 

 to form a pure spectrum with sun-light as usual, employing instead 

 of a screen a vessel containing a decoction of the bark of the horse- 

 chestnut, or a slab of canary glass, or some other highly sensitive 

 medium, and then to interpose the medium to be examined, which, 

 if fluid, would have to be contained in a vessel with parallel sides 

 of glass. Glass itself ceases to be transparent about the region 

 corresponding to the end of the author's map, and to carry on these 

 experiments with respect to invisible rays of still higher refrangibility 

 ■would require the substitution of quartz for glass. The reflecting 

 power of a surface with respect to the invisible rays may be examined 

 in a similar manner. 



Tlie eff'ect produced on sensitive media leads to interesting informa- 

 tion respecting the nature of various flames. Thus, for example, it ap- 

 pears that the feeble flame of alcohol is extremely brilliant with regard 

 to invisible rays of very high refrangibility. The flame of hydrogen 

 appears to abound in invisible rays of still higher refrangibility. 



By means of the phenomena relating to the change of refrangibi- 

 lity, the independent existence of one or mere sensitive substances 

 may frequently be observed in a mixture of various compounds. In 

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

 ration of organic compounds. The phenomena sometimes also aff"ord 

 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 circumstances render 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 ])hosphores- 

 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 exjAains 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, 



"2. "Analytical Researches connected with Steiner's Extension of 

 Malfatti's Problem." By Arthur Cayley, M.A., Fellow of Trinity 

 College, Cambridge. Communicated bv J. J. Svlvester, Esq., F.R.S. 

 Received April 12, lcS52. 



