88 



ON THE SPECTROSCOPE. 



By Q. J. Snelus, Assoc. R.S.M, (Workington). 



DeUvered to the Workington Society (April 26th, ia76), and before the 

 Cumberland Association (May 1st, 1876,) at Whitehavpn. 



The invention of the' Spectroscope may fairly be considered one of 

 the most important triumphs of modern science. 



In explaining its construction and use it will be advisable that I 

 remind you briefly of the nature of light. Modern Physicists hold that 

 light is the result of vibrations of the particles of an extremely attenuated 

 medium, termed the luminiferous ether, which is supposed to permeate all 

 space. Just as touncl is the result of motion imparted to the air, which 

 motion is propagated in the form of waves, the size of the wave determining 

 the pitch of the sound ; so light is the result of wave motion among the 

 particles of the luminiferous ether, different sized waves producing 

 differently coloured lights. But while the motion of the air producing 

 sound is comparatively slow, the highest musical sound that the ear 

 is capable of detecting being produced by 38,000 vibrations per 

 second, and the lowest by 16, the smallest number of vibrations 

 capable of affecting the eye and producing a red ray is about 451 millions 

 of millions per second and the length of the wave is only ,^^ ^^^ th 

 part of an inch. As the waves decrease in length and increase in velocity 

 the eye interprets the result as orange, yellow, green, blue, and violet, 

 respectively, till we get up to 789 millions of millions per second with 

 wave lengths of ^,\,. th the H line in the violet, which is the most rapid 



^ 04,000 



wave the eye can register under ordinary circumstances. White light is 

 the result of vibrations of several degrees occuring together. When 

 white light impinges upon different objects they stifle some rays and either 

 reflect or transmit others. When white light falls perpendicularly upon 

 colourless glass, if the two surfaces are parallel, the ray passes straight 

 through, it is neither bent oiit of its course nor changed in any way, but if 



