45 



of an extraordinary quantity of the vapour of Sodium in their 

 composition. 



One point of importance to be ascertained by means of the 

 " Meteor Spectroscope" is whether shooting Stars and their 

 luminous trains, are composed of porous or of solid matter, 

 and from Spectrum Analysis of the August Meteors the pro- 

 bability is that their composition is a mineral substance in 

 which sodium is one of the principal ingredients. 



• From the study of mineral matter in a state of incandes- 

 cent vapour, Spectrum Analysis has become of the greatest 

 importance. Much is also learnt by observations on the light 

 transmitted by or reflected from solutions of colored sub- 

 stances, however small the proportion in which they may be 

 present, and in this way the Spectroscope has been very 

 successfully applied to the Microscope. In examining the 

 solutions prepared for this part of the subject there will be 

 seen on the stage of the Microscope what have been named 

 Fraunhofer's dark lines, which have been made by Professor 

 Kirch off the key by which this kind of writing can be de- 

 ciphered and read. 



When a ray of light falls upon a glass prism two different 

 actions take place ; first the ray is refracted or bent out of its 

 course, secondly, it is opened or spread out like a fan. This 

 last action is called dispersion ; the dispersion of any part of 

 the spectrum is proportional to the angular interval between 

 two rays of nearly equal refrangibility ; both these actions 

 depend on the substance employed in the formation of the 

 prism. The size and character of a Spectroscope, the quality 

 and number of prisms required, with such refracting angles 

 as will produce the greatest dispersion with the least loss of 

 light, should be regulated by the work required of it. 



For the detection of metals, the spaces, and bands by which 

 their presence is indicated, are consj^icuously shown by an 

 instrument that will display the chief lines of the Solar 

 Spectrum, but there are many thousand lines discernible with 

 more powerful apparatus, and many lines that appear single 

 under ordinary circumstances,are found to be double ormultiple 

 when examined by superior means. 



As a means of research, the application of Spectrum 

 Analysis to the Microscope has not yet been attended with 

 results of so decided a character as the study of mineral 

 matter in a state of incandescence, although by such applica- 

 tion we can detect and measure very minute quantities, and 

 also compare the spectra of two solutions together. 



It is much more difficult to learn what is and what is not 

 characteristic in objects prepared for examination in this kind 



