588 



SUMMAEY OF CURRENT RESEARCHES RELATING TO 



tionately larger dispersion than solids of equal refractive index. For 

 the homogeneous-immersion method, however, fluids are required 

 which agree in refraction and dispersion with the glass of the objec- 

 tives. Finally, it is found that with an increasing total dispersion 



Refracting Substances. 



Fluor spar 



Distilled water, 22° C 



Sulphuric acid^hydr.) i*5 per cent. .. 



Sugar candy — sol. io per cent 



Alcohol, 38 • 8 per cent 



86-8 „ 



Calcspar (e) Hofm. IIJ 



Chloride of sodium— sol. 8 "6 per cent. 



Sugar candy— sol. 30 per cent 



Chloride of ammonium — sol. 9' 7 per cent. 



Arragonite (7) 



Glycerine, 49*7 per cent 



Acetic acid, 97*6 per cent 



Chloride of zinc — sol. 18 per cent. 

 Chloride of calcium — sol. IG'7 per cent. 



Topaz (3) 



Quartz (o) Hofm. I 



Glycerine, 1 00 per cent 



Chloride of sodium — sol. 26 "6 per cent. 



Topaz (a) 



Chlori'le ofammonium — sol. 24 "8 percent 

 Chloride of zinc — sol. 31*0 per cent. .. 



Quartz (c) Hofm. III. R 



Crown glass 



Heavy spar (7) 



Chloride of calcium — sol. 40 '6 T">er cent. 



Heavy spar (a) 



Crown glass (Merz IV.) 



Turpentine 



Rock salt, 22" C 



Arragonite (o) 



Calcspar (o) Hofm. Ill » ., 



Flint glass 



Naphthaline in Benzol 



Benzine, A 



Benzole, pure 



Sassafras oil 



Oil of anise 



Thallium glass 



Flint glass (Merz II.) 



Monobromide of naphthaline 



Bisulphide of carbon 



13-7 



Oil of cassia 



St. 

 V. W. 



v.'b. 



V. W. 



V. O. 



v. W. 



R. 



V. W. 



R. 



V. W. 



R. 

 V. W. 



Lo. 



H. 

 V. W. 



H. 

 V. W. 



St. 



R. 

 V. W. 



Lo. 



Ve. 

 V. W. 



Ve. 

 B.P. 



Ve. 

 V. W. 



Ve. 

 V. W. 



v.'w. 



•01004 

 •01305 

 •01350 

 •01351 

 •01368 

 •01376 

 •01381 

 •01428 

 •01451 

 •01466 

 •01477 

 •01493 

 •01501 

 •01559 

 •01599 

 •01691 

 •01711 

 •01712 

 •01715 

 •01715 

 •01720 

 •01757 

 ■01777 

 ■01867 

 •02043 

 •02106 

 •02145 

 •02194 

 •02311 

 •02904 

 •02950 



• 03032 

 •03086 

 •03815 

 ■03853 

 •03893 

 •04360 

 •0.=)977 

 •06709 

 •07008 

 •08369 

 •08411 



• 08576 

 •11270 



there is generally a larger partial dispersion in the blue. It is to 

 this point, as it seems to me, that the opticians will in future have to 

 direct theii* attention in the correction of the chromatic aberration. 



A comparison of the above three conditions can, however, only be 

 made by means of a tabular statement of the measurements hitherto 



