On the Length of Waves of certain bright Lines in the Spectrum. 259 



fettered by cohesion, the integral of which bears comparison with 

 the more intense of the chemical forces. The H in its connexion 

 with the metal may be compared to the H in the hydrocarburet 

 C*H, which, being one-half CH 2 the olefiant, and one quarter 

 C 2 H 4 etherine, we may by analogy hold as possible, yet, like a 

 metallic hydride, having the affinity of its constituents for oxygen 

 and the other electro-negative elements too exalted to exist in a 

 state to be recognized. In pyroxylic spirit it appears combined 

 with water, C^H .HO*; in chloride of methyle, C^HCl, com- 

 bined with chlorine, &c. 



However this may be, it cannot be disputed that chemical 

 elements unite in modes that, estimated dynamically, are speci- 

 fically distinct. Besides those above noted, there seems to be 

 another, as in the case of chloride of nitrogen, where not only 

 force, but heat and light accompany the disunion of elements 

 — is evolved instead of being absorbed. In the usual case, force 

 or heat causes the separation ; in the fulminate, the separation 

 causes (apparently) force and heat. Such considerations must 

 enter into any system of classification of chemical com- 

 pounds that is not quite artificial and arbitrary. To include 

 under the same type a liquid of which the elements are in a 

 burnt condition, with another the major part of which is in an 

 unburnt condition, is simply to ignore the dynamical theory of 

 heat, to reject as a guide a principle that has never failed to yield 

 rich returns to those who have resigned themselves entirely to 

 its guidance in the study of nature. 



Edinburgh, August 1, 1863. 



XXXY1. Determination of the Length of the Waves of certain bright 

 Lines in the Spectrum. By Dr. John Mtller of Freiberg* 



AS well-divided glass screens offer the simplest and most 

 accurate means of ascertaining the length of the waves for 

 the differently coloured rays, I have had recourse to an unex- 

 ceptionably perfect screen that I recently obtained from Nobert, 

 of Barth in Pomerania, to determine the length of the wave of 

 the red lithium line (Li a), the yellow sodium line (Naa), and 

 the blue strontium line (SrS). This screen had 2001 lines in 

 the width of 4 Paris lines ; the distance from the middle of one 

 line to the middle of the following one, a magnitude which we 

 shall designate by b, amounted to ;,, -002. It was so placed on 

 the centre stage of a small goniometer of Babinet's construction, 

 that its plane was at right angles to the axis of the telescope 

 provided with the slit. A small gas-lamp was then placed in- 



* Translated from Poggendorff's Annalen, vol. cxviii. p. 641, and com- 

 municated by W. G. Lettsom, Esq. 



S2 



