138 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



been removed with the help of a Sprengel pump. With an 

 apparatus of this description, the disks and arms spun around 

 rapidly when luminous rays were directed upon it, but ob- 

 scure heat rays produced no effect upon it. When sub- 

 mitted to the action of light from which 95 per cent, of 

 the heating rays had been cut out by the interposition of a 

 plate of alum, the disks still revolved, though with some- 

 what diminished velocity. Contrary to expectation, it was 

 the blackened faces of the disks that were repelled by the 

 light. 



THE SPECTEOSCOPE W 7 ITII A FLUOEESCENT OCULAE. 



In observing the most refrangible portions of the spec- 

 trum it is common to use two methods either the spectrum 

 falls upon a plate sensitive to the ultra violet rays, or else 

 the spectrum falls upon a fluorescent substance which has 

 the property of revealing these rays. To this a third meth- 

 od is now added by Soret, whose application is very simple. 

 Soret's method consists in this, that he inserts a plate of trans- 

 parent fluorescent substance in the tube of the spectroscope, 

 and observes the spectrum with a telescope whose ocular is 

 inclined to its axis. With a plate of uranium glass the flu- 

 orescent spectrum is well seen. The best substance, how- 

 ever, is a somewhat concentrated solution of aesculin, by 

 means of which the spectrum may be traced up to the line 

 O. This simple apparatus affords an especially convenient 

 method for examining the spectrum of the ultra violet por- 

 tion of the solar light. 19 C, VIL, 232. 



ON THE INTENSITY OF THE LIGHT EEFLECTED FEOM GLASS. 



Dr. Glau states that hitherto the investigations of the 

 properties of reflected light have, by preference, referred to 

 the ratio of the two principal components to each other, as 

 well in respect to their phases as to their intensity; and in 

 but few cases has it been attempted to make a direct com- 

 parison of these two components in regard to the incident 

 light. The only experiments on the intensity are found in 

 Arago's works, and are quite fragmentary, and on that ac- 

 count the inquiry has been undertaken anew by Dr. Glau, 

 in order especially to test the accuracy of Cauchy's for- 

 mula. His observations give the ratio of the intensity of the 



