No. 2.] BRITISH ASSOCIATION MEETING. 135 



The chemist and the astronomer have joined their forces. An 

 astronomical observatory has now appended to it a stock of re- 

 agents such as hitherto was only to be found in the chemical 

 laboratory. A devoted corps of volunteers of all nations, whose 

 motto might well be Uhiqite, have directed their artillery to every 

 re2;ion of the universe. The sun, the spots on his surface, the 

 corona and the red and yellow prominences seen round him dur- 

 ing total eclipses, the moon, the plauets, comets, auroras, nebulae, 

 white stars, yellow stars, red stars, variable and temporary stars, . 

 each, tested by the prism, was compelled to show its distinguish- 

 ing prismatic colours. Rarely before in the history of science 

 has enthusiastic perseverance directed by penetrative genius pro- 

 duced within ten years so brilliant a succession of discoveries. 

 It is not merely the cliemistry of sun and stars, as first suggested, 

 that is subjected to analysis by the spectroscope. Their whole 

 laws of being are now subjects of direct investigation ; and already 

 we have glimpses of their evolutional history through the stupen- 

 dous power of this most subtle and delicate test. We had only 

 solar and stellar chemistry ; we now have solar and stellar physi- 

 ology. 



3. MOTION OF THE STARS. 



It is an old idea that the colour of a star may be influenced by 

 its motion relatively to the eye of the spectator, so as to be tinged 

 with red if it moves from the earth, or blue if it moves towards 

 the earth. William Allen Miller, Huggins, and Maxwell showed 

 how, by aid of the spectroscope, this idea may be made the foun- 

 dation of a method of measuring the relative velocity with which 

 a star approaches to or recedes from the earth. The principle is, 

 first to identify, if possible, one or more of the lines in the spec- 

 trum of the star, with a line or lines in the spectrum of sodium, 

 or some other terrestrial substance, and then (by observing the 

 star and the artificial light simultaneously by the same spectro- 

 scope) to find the difi"erence, if any, between their refrangibilities. 

 From this diff'erence of refrangibility the ratio of the periods of 

 the two Hghts is calculated, according to data determined by 

 Fraunhofer from comparisons between the positions of the dark 

 lines in the prismatic spectrum and in his own " interference 

 spectrum " (produced by substituting for the prism a fine grating). 

 A first comparatively rough application of the test by Miller and 

 Huggins to a large number of the principal stars of our skies, 

 including Aldebaran, a Orionis, b Pegasi, Sirius, a Lyrce, Capella, 



