C. GENERAL PHYSICS. 153 



known to the French artists. He quotes a glass manufactured 

 by Barclon, whose aperture is 1.6 inches, which, with a 

 magnifying power of sixty times, shows the companion to 

 Polaris. l3e Abbadie calls attention to this matter in order 

 to indicate to astronomical amateurs what degree of visibility 

 can be attained with small instruments, and especially since 

 it shows that in a telescope the perfection of the workman- 

 ship of the lenses is of more importance than their great 

 dimensions. 6 i?, 1873, 92. 



SPECTRA OF SIMPLE AND COMPOUND BODIES. 



Lockyer, in a recent letter on the subject of spectral anal- 

 ysis, states that he has studied various series of salts : First, 

 those series in which the atomic weights vary ; second, those 

 in which the associated elements vary ; and among his con- 

 clusions we note the following : 



1. In compounds of lead, the diminution of the spectral 

 rays, both in length and number, coincides with the increase 

 of the atomic weight of the non-metallic element in the com- 

 pounds under consideration. In compounds of barium with- 

 fluorine, he finds that its spectra are far simpler than those of 

 lead. So also with strontium and magnesium, and their com- 

 pounds of fluorine, there are, as in the case of barium, only four 

 lines in their spectra. He thinks that this anomaly is due to 

 the excessively refractory nature of these fluorids, preventing 

 them from volatilizing so readily as do the compounds of 

 lead. The compounds of sodium with chlorine and fluorine 

 and iodine have given results quite opposite to those given 

 by the compounds of lead ; that is to say, the iodine, etc., 

 produce metallic spectra very complete. Lockyer has also 

 discussed the diflerence between the spectra produced by a 

 flame and those given when we make use of the electric 

 spark, and he finds the difl*erences are such as are probably 

 due only to the diflerence in the intensity of the heat and 

 light. He lias also investigated the spectra of the above- 

 mentioned chemical compounds when heated in hydrogen as 

 well as in atmospheric air, and concludes that a compound 

 body has a spectrum as well defined as that of a simple body; 

 but that, while the spectrum of this latter consists of lineS 

 whose number and thickness augment with the molecular 

 density, the spectrum of a compound body, on the other 



G2 



