420 PROCEEDINGS OF THE AMERICAN ACADEMY 



In applying the above methods, I have used prisms with brass 

 frames, and have cemented the glass-plates either with common or with 

 marine glue, the latter being employed for aqueous solutions. Good 

 workmanship would doubtless make it possible to fit the plates to the 

 sides of the prisms so that they could be held in their places by springs, 

 the prisms being perfectly tight; but I have not found this to be the 

 case with prisms from German workshops which I have examined. 



The process which I have given above furnishes, of course, a new 

 application of the spectroscope to quantitative chemical analysis, — all 

 the results obtained by Landolt with the spectrometer being obtained 

 with the spectroscope alone ; but it is hardly necessary to say that a 

 good spectrometer is an instrument greatly to be preferred, since it 

 may be used also as a spectroscope, and since direct methods are always 

 better than those of comparison. 



