INTRODUCTION. 



RECENTLY microscopic technology has risen to 

 an importance undreamed of in its early days. 

 The perfection of the microscope, by whose help 

 so many beautiful and important discoveries are 

 made, has given us such an insight into the nat- 

 ural history of the cell as to stimulate the study 

 of elementary organs, so far as possible, with 

 all available aids. The spectroscope, the polar- 

 iscope, and the induction coil, placed in our hands 

 by Bunsen, Huygens, and Faraday, are applicable 

 and must augment the value of the instrument 

 first given us by Hans and Zacharias Janssen ; 

 and even photography has of late been employed. 

 Physics has thus striven to bring this instrument 

 to as great a degree of perfection as possible ; 

 it remains for chemistry to find means of recog- 

 nizing and rightly understanding the composition 

 of the objects we investigate. In other words, if 

 we employ a thorough system of chemical analysis 

 with the optical apparatus we shall be able to 

 answer all questions lying within the range of pos- 

 sibility. It is this analysis, applied to objects 



xi 



