184 ACTINISM AND ELECTRICITY. 



thing is quite evident, electricity suffers a disturbance 

 of one order, by light; and an excitement of another by 

 its associated principles in the sunbeam. If a yellow 

 glass is interposed between the galvanic arrangement 

 and the sun, the electro -chemical precipitation goes on 

 in the same manner as it would in perfect darkness, 

 and no extra excitement is produced upon the plates of 

 the battery. From this it would appear that actinism 

 and. not light is to be regarded as the disturbing power.* 

 It has already been shown that yellow media possess the 

 power of stopping back the chemical agent. 



We have already detailed many of the peculiarities of 

 the different varieties of Phosphori, which would seem 

 to be the result of light. Phosphorescence is probably 

 excited by those rays which produce no direct effect 

 upon the eye. If we spread sulphuret of calcium upon 



* Memoir on the Constitution of the Solar Spectrum, presented 

 at the meeting of the Academy of Sciences, 1842, by M. Edmond 

 Beequerel; Des effets produits sur les corps par les rayons solaires, 

 par M. Edmond Becquerel, aide au Museum d'Histoire Naturelle : 

 Memoire presente a 1' Academic des Sciences, le 23 Octobre, 1843. 

 " Dans le courant de ce- memoire, j'ai employe les noms de 

 rayons luinineux, chimiques, et phosphorogeniques, pour designer, 

 dans chaque cas, la portion des rayons solaires qui agit pour pro- 

 duire, on particulier, les effets lumineux, chimiques, et phospho- 

 rogeniques; mais cela est sans prejudice de 1' opinion que je viens 

 d'emettre touchant 1'existence d'uii seul et rneme rayonnement." 



" My reply is this,'' says M. Arago, in his paper entitled 

 Considerations relative to the action of Light : " It is by no means 

 proved that the photogenic modifications of sensitive substances 

 result from the action of the solar light itself. The modifications 

 are, perhaps, engendered by invisible radiations mixed with light 

 properly so called, proceeding with it, and being similarly re- 

 fracted. In this case, the experiment would prove not only that 

 the spectrum formed by these invisible rays is not continuous, 

 that there are solutions of continuity as in the visible spectrum,, 

 but also that in the two superposed spectra these solutions cor- 

 respond exactly. This would be one of the most curious, one 

 of the most strange results of physics." Taylor's Scientific- 

 Memoirs. 



