48 The Microscope. 



of the spectrum test, which gives to its application so great a value 

 and so extensive a scoj)e. It responds distinctly and immediately 

 where the highest magnifying powers of the best microscopes can 

 no longer give us any information. It gives us a most valuable 

 reaction for every alteration or change which blood undergoes when 

 acted upon by physical or chemical agencies ; it analyzes the flames 

 of gases, and those of mineral and metal poisons, and unravels the 

 secrets of crime, depending upon the administration of these 

 destructive agents, with wonderful precision and unimpeachable 

 certainty. 



SPECTROSCOPIC ANALYSIS. 



By spectroscopic analysis, we understand a scientific process or 

 procedure in which light, solar, stellar or artificial, is made use of to 

 analyze and demonstrate both organic and inorganic substances. 

 The instrument employed consists of a system of prisms and lenses 

 by which rays of light are broken up into a series of colored tints 

 called a spectrum, and which offers to the eye all the colors of the 

 rainbow with great beauty and brilliancy. We call this instrament 

 a spectroscope, and if adjusted to a microscope, a micro -spectro- 

 scope. The spectroscope may have one or many prisms ; the more 

 good prisms a spectroscope has, the higher and greater is its 

 dispersive power. Two or more telescopic tubes may enter into its 

 construction. One tube is provided with a slit arrangement to 

 admit and regulate the admission of light. The source of light 

 may either be an oil or petroleum lamp placed before the slit, or we 

 may utilize sun and starlight ; other illuminating sources are 

 furnished by the oxygen lime-light, by burning magnesium, the 

 electric arc, and various other artificial means. One of the tubes 

 carries also one or more collemator lenses, which are necessary to 

 collect the admitted rays and to make them parallel. The light, in 

 passing through the prism or prisms, is refi'acted, and its rays 

 broken up in a colored image or spectrum, which passes to the 

 observer's eye and is appreciated by the retina. By appropriate 

 means we can also throw the image upon a white screen. For some 

 instruments there is a very useful and necessaiy scale attached, 

 which divides the spectrum in a certain number of degrees, 

 usually 140. It is very useful to locate very definitely the bright and 

 dark lines and absorption bands, especially when working with 

 artificial light, which cannot produce the Frauenhofer sunlines. The 

 scale was introduced by Steinheil. 



In the micro-spectroscope, the mechanism is such that two 



