Intelligence and Miscellaneous Articles. 79 



RESEARCHES ON THE VARIATION IN THE DISPERSION OF LI- 

 QUIDS UNDER THE INFLUENCE OF HEAT. BY M. J.-B. BAILLE. 



In a previous research I had investigated the influence of heat on 

 the refraction and dispersion of solids whose expansion is regular. 

 The great distinction which this research received from the Academy- 

 led me to extend these investigations to liquids. Several researches 

 had already been made on this subject, among others those of 

 Messrs. Dale and Gladstone (I860) and M. Fouque (1867) ; but 

 these physicists had more especially in view the refraction of liquids ; 

 and as in my previous investigations I had arrived at the conclusion, 

 that the dispersion of solids increases with heat, I wished to ascer- 

 tain if the dispersion of liquids was also subjected to some special law. 

 The apparatus and the method I used have already been described. 

 Since, from the nature of the case, it was necessary to work rapidly, 

 the approximation is not so close as in my former experiments. I 

 have used the indices of the three Fraunhofer's lines C, D, and F, 

 and have obtained a large number of results, among which I will 

 cite the following : — 



Distilled Water. 

 It was first ascertained that the refractive index diminishes pro- 

 gressively from to 100 degrees, and that the variation of this 

 index remains very feeble up to 6 degrees, when it commences to 

 increase with the temperature. The vicinity of the point 4 degrees, 

 corresponding to the maximum density, did not appear to influence 

 the refractive index, as has been found by M. Jamin and Messrs. 

 Dale and Gladstone. F n — C». 



C„. I) n . F„. Units of the 



fifth place. 



2-00 1-33251 1-33482 1-33897 646 



3-50 1-33248 1-33479 1-33894 646 



4-50 1-33247 1-33479 1-33894 647 



5-25 1-33243 1-33475 1-33890 647 



8-00 1-33231 1-33461 1-G3874 643 



15-25 1-33165 1-33392 1-33799 634 



Omitting the intermediate determirations. 

 100-00 1-31799 1-31943 1-32284 485 



It is seen from this Table that the dispersive power measured by 

 the difference between the extreme indices is constant, or even 

 slightly increases, from 2 to 5 degrees, and that from this point it 

 diminishes regularly and pretty rapidly. 



Though these numbers differ somewhat from those of Messrs. 

 Dale and Gladstone, this constancy of dispersive power up to 5 de- 

 grees is undoubted ; for it is found in their numbers — a coincidence 

 the more remarkable that they have not noticed this feature. 

 Sulphur et of Carbon. 



C„ D M . F w . D»-rG. F n -C,„ 



In units of the In units of the 

 fourth order fourth order. 



14. ...1-6213 1-6309 1-6556 96 247 



25.... 1-6156 1-6248 1-6492 92 244 



It is thus seen that under the influence of heat the index of sul- 

 phuret of carbon considerably diminishes. The dispersive power 



