160 THE ROYAL SOCIETY OF CANADA 



also an attempt made with a freezing microtome. Thin slices were 

 ultimately obtained by freezing the rubber in liquid air and then 

 cutting it with a sharp knife or razor. Slices obtained in this way 

 were still too thick for satisfactory work and it was necessary to obtain 

 sheets which had been rolled out by mechanical means. These were 

 quite thin and could be readily used in all experimental work. 



Preliminary tests were made to determine whether there were any 

 absorption bands produced in a continuous spectrum. A quartz 

 uviol spectrograph was used for this determination. As a source of 

 light, a Nernst lamp was used, and also an arc in which different 

 metals could be inserted as terminals. A photograph of the spectrum 

 produced by the Nernst was first obtained and directly below it a 

 photograph of the spectrum after it had passed through a thin sheet 

 of rubber mounted directly in front of the slit of the spectrograph. In 

 this way the two spectra could be readily compared and their charac- 

 teristics noted. 



The photographs obtained show that rubber absorbs light and 

 that the more refrangible rays are more readily absorbed, so that 

 any change or alteration in the characteristics of the rubber must be 

 due principally to these rays. These results are, however, not sufifici- 

 ently quantitative in nature to warrant any definite assumption as to 

 the amount of light that is being actually absorbed. 



The second stage of the experimental work was undertaken with 

 the object of determining more definitely in a quantitative way a 

 measure of this absorption. A suitable method of investigation is 

 afforded by the photo-electric cell. The cell used in this work was of 

 the round bulb type, about 5 cm. in diameter and made of glass. The 

 arrangement of the apparatus was as shown in the following diagram. 

 (Fig. 1.) 



The source of illumination (A) was a Nernst lamp, the filament of 

 which was focused by a quartz lens (L) on the slit of a monochromatic 

 illuminator (M). The light on emerging from (M) fell on the photo- 

 electric cell (C), the silvered surface being charged to a potential of 6 

 volts by a battery (B). The filament of the cell was joined through 

 insulated connections to one pair of quadrants of a quadrant electro- 

 meter (Q), the other pair of quadrants being earthed. The quadrants 

 joined to the cell could be earthed by the earthing needle (N). The 

 needle of the electrometer was charged to a constant high potential by 

 a Tucker Hydroscopic Battery (H). The electrometer when adjusted 

 had a sensibility of 330 divisions per volt. The sensibility curve is 

 shown in Fig. 2. 



