146 TIIE PHOSPHORESCENCE OF BODIES. [MEMOIR VIII. 



front of it, so that when the spark passed, a brilliant 

 glow arose in the spar, which was at once viewed 

 through the analyzer of the instrument. But though 

 the experiments were made both by daylight and lamp- 

 light, no kind of effect could be detected. Had any 

 molecular change occurred, it could not have escaped 

 notice. 



In Fig. 16, a b is the polariscope, c the flat piece of 



fluor-spar, b the analyzer, d d 

 the wires giving the electric 

 spark. 



These experiments were first 

 made by using as the analyzer 

 a doubly refracting achromatic 

 prism ; they were, however, re- 

 peated with a Nicol, in which 

 the eye is not disturbed by a 

 bright image as in the other 

 case. Having fixed the plate of polished fluor in the 

 polariscope, it was readily perceived that it possessed 

 naturally a structural arrangement, for there were cloudy 

 spaces or lines in it which contrasted with the faint 

 white light passing in the adjacent parts. It was also 

 seen that this structural arrangement could be deranged 

 in a transient manner, either by pressure or an unequal 

 warming, as is well known of other bodies ; but when a 

 powerful electric discharge was passed near the spar, 

 and a brilliant phosphorescence took place, no impres- 

 sion could be detected. Even when the iron wires rest- 

 ed on the spar, and the explosion passed over its surface, 

 nothing was perceptible except along the line between 

 the ends of the wires, where the surface was roughened 

 or abraded by the force of the discharge. 



But though these experiments with polarized light 

 give a negative result, or, at all events, prove that a 



