502 



HISTORY OF SCIENCE. 



It would lead us far beyond our limits to state the facts from which 

 observers have been able to infer the existence in the sun of several 

 gaseous strata in which the different elements are arranged. Mr. 

 Lockyer's spectroscopic researches have enabled him to specify the 

 chemical elements contained in each layer, as in the following table : 



_, (An unknown element (?). 



The Corona .... ] Sub-in candescent hydrogen. 



( Incandescent hydrogen. 



\ An unknown element (?) for which the name Helium 

 The Chromosphere . . . < is proposed. 

 7 Calcium. 

 (^Magnesium. 



The region of the Solar Spots . 



I Iron. 

 Manganese. 

 Cobalt. 

 Nickel. 

 Copper. 

 The Keversmg Layer . . \ Zinc. 



I Potassium. 

 I Strontium. 

 I Barium. 



Cadmium. 

 I Lead. 



The reader must have observed how remarkably the results of the 

 spectroscopic observation of the heavenly bodies has tended to con- 

 firm the nebular hypothesis of Laplace (page 269). The chemistry of 

 nebulae, stars, and suns was but a few years ago a thing which even wise 

 philosophers deemed an impossible attainment. Now it has come to 

 pass that, after Galileo's discoveries and Newton's great conception of 

 universal gravitation, no additions to our knowledge have more deeply 

 modified our ideas concerning the universe at large than those new 

 facts which the spectroscope has revealed. It was for this reason 

 imperative that a chapter should be devoted to the notice, however 

 incomplete, of the revelations of the spectroscope. Necessarily a mul- 

 titude of interesting researches have been passed over in silence, and 

 some remarkable developments of spectroscopy altogether omitted. 

 Such, for example, is the application of the spectroscope to the micro- 

 scope by Mr. Sorby, in which this subtle mode of analysis is made to 

 reveal the presence of substances which would defy all other methods 

 of detection. Thus, a droplet of blood, less than a pin-head in size 

 nay, even the thousandth part of a grain can infallibly be recognized, 

 and also the state of that blood with regard to oxidation revealed. 



This chapter has been occupied with the description of observed 

 phenomena, from which many important discoveries have resulted, but 

 from which no comprehensive general theory has yet emerged. In 

 truth, the facts treated of here are in the condition of the facts of 



