CHAPTER IV. 



FACTORS OF A CORPUSCLE: AN EXPERIMENT. 



Concerning corpuscles, we have so far found that they 

 are little bodies, laden with negative electricity, dancing off 

 from glowing metals, incandescent carbon or gas flames; 

 and we have now a very reasonable curiosity to know 

 (1) how fast they travel, (2) what electric charge they 

 carry, and (3) what they weigh. If we but knew these 

 three elements, we may be sure we should know the corpus- 

 cles fairly well, so far as their extrinsic qualities go. And, 

 if our search is to continue, it is to the discovery of these 

 elements that we must now proceed. 



These values are readily determinable for corpuscles as 

 they fly off from hot metals, but it may be more convenient 

 to derive them, here, for corpuscles emitted by metals under 

 the impact of ultra-violet light. We are already acquainted 

 with the fact that glowing metals give off negatively elec- 

 trified particles, or corpuscles; but it is an entirely new 

 statement to say that metals, without the application of 

 any heat whatever, will give out these same corpuscles on 

 mere exposure to light. But the fact is without difficulty 

 demonstrated by charging a newly cleaned surface of zinc 

 with electricity, and exposing it to the light from an arc 

 lamp ; for the zinc plate rapidly loses its electrification, and, 

 reasoning anologous to that previously applied, leads irre- 

 sistibly to the conclusion that the loss is occasioned by cor- 

 puscles flying away with it. 



It turns out, however, that the active constituent of the 

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