412 Scientific Intelligence. 



weights thus obtained for equal volumes of the various liquid and 

 solid species are evidently the specific gravities of these species ; 

 that of hydrogen at the standard temperature and pressure being 

 unity (H„ = 2 - 0). They are at the same time the integral weights 

 of the species compared." Notwithstanding this clear statement 

 in both papers that it is hydrogen at 0° and 760 mm which is to 

 serve as the unit of specific gravity alike for gaseous, liquid and 

 solid species, the reader will find in these papers, and also in the 

 first edition of the author's New Basis for Chemistry (1887), an 

 error in the subsequent calculation. The problem having been 

 approached from the comparison of the weights of equal volumes 

 of liquid water at 0° and 100°, and of water-vapor at 100° and 

 760 mm , by an inadvertence (until now unperceived) the weights 

 alike of hydrogen gas and of water-vapor at the latter tempera- 

 ture were substituted for their weights at 0° and 760 mm ; thus lead- 

 ing to a grave error in the figure given for the integral weight of 

 liquid water, and of bodies for which it serves as the unit of spe- 

 cific gravity, and making it equal 29244. In fact, however, tak- 

 ing as the unit of weight that of the litre of hydrogen gas at 

 standard temperature and pressure (0° and 760 mm ) and comparing 

 it with that of liquid water at 100° (its temperature of formation 

 at 760 mm ), when a litre of it weighs 95 8 '78 grams, we have : 



0-0896 : 958-78 : : 2 : x = 21400-3. 

 This value is thus alike the specific gravity of the liquid on the 

 hydrogen basis and its integral weight, which, if we take H 2 0= 

 17-96, corresponds vei'y closely to 1192(H 2 O)=2140S ; ice being 

 probably 1094(H 2 O), calcite, 584(CCa0 3 ) and aragonite, 630 

 (CCa0 3 ). While the writer regrets this error in calculation, made 

 in direct contradiction to the principles laid down by him in both 

 of the papers cited, it will be seen that its correction in no way 

 affects their argument, which he hopes to develop further at an 

 early day. 



"Washington, D. C, February 22, 1888. 



6. Absorption. Spectra. — The relation of absorption spectra to 

 the various physical constants of the substances which afford the 

 spectra has not been fully made out. Fb. Stenger's experiments 

 conduct him to the conclusion that the absorption of light by 

 various substances depends primarily upon the size of the physical 

 molecule. Changes in the state of aggregation, or changes pro- 

 duced by different media in which a substance is dissolved pro- 

 duce absorption spectra of different character only when the 

 state of the physical molecule is also altered. The author dis- 

 cusses, from this point of view, the law of Kundt connecting the 

 index of refraction and the dispersive power of a medium in 

 which a substance is dissolved with the displacement of absorp- 

 tion bands toward the red end of the spectrum. Vogel's re- 

 searches upon the absorption of dyes in the solid state, obtained 

 by staining gelatine films, and their absorption in the liquid 

 state is also adduced as an evidence of the truth of the author's 



