THERE ARK MORE THAN THKEE IMPONDERABLES. 215 



ins that rock-salt is perfectly transparent to calorific rays, that glass is much less so, 

 that Rochelie salt, alum, and sulphate of copper are almost, opaque ? It is surely impos- 

 sible to confound the phospborogenic emanation of an electric spark with its rays of 

 light ; the latter pass perfectly through glass, the former do not. So far as the eye can 

 distinguish, an electric spark, the rays of which have passed through glass, differs in no 

 respect from one the rays of which are received directly into the eye. If we consider 

 the constitution of such a rav, previous to and after its passage through glass, the eye 

 can disc-over no difference; but, as respects the phosphorogenic emanation, there was 

 something existing iu that ray at the first of these epochs which had ceased to exist in 

 it at die second ; a something not having the quality of communicating any impression 

 to the organ of vision ; and that which we cannot see, surely no man will acknowledge 

 to be light. 



992. But the reader may inquire, What has all this discussion of the characters of the 

 phosphorogenic emanation to do with the existence of the tithonic rays as a fourth im- 

 ponderable ! A few words will show. From these considerations and experiments, 

 we have arrived at the conclusion that there exist in the beams of an electric spark 

 invisible rays, which are therefore totally distinct from light. They occupy the same 

 spectrum region as the tithonic rays which decompose iodide of silver ; their leading 

 character is, that glass, which is transparent to the rays of light, is opaque to them. 



993. But the admission of this fact breaks down at once the doctrine of a trinity of 

 imponderables, and compels us to enlarge our list of those living forces of chemistry. 

 The great obstacle which is in the way of admitting the tithonic rays as a fourth im- 

 ponderable, is in the circumstance that it would impress a very serious change on that 

 science, and apparently afford an argument of weight against the mathematical theory 

 of light I believe that some great generalization will hereafter prove that all these 

 imponderables are modifications of one primordial principle. I also believe that some 

 capital experiment will hereafter show that the forty different metals we are acquainted 

 with are merely modifications of one or two more simple forms ; but these are things 

 that we are unable to deal with now ; and viewing the experiments which have been 

 made in the last few years, not as mathematicians, but as chemists, all men must ac- 

 knowledge that our prevailing doctrines of the nature and number of the imponderables 

 are liable, before long, to undergo a very serious modification. 



994. The admission that the phosphorogenic emanation and light are principles 

 differing from the tithonic rays and from each other, relieves us of much difficulty in 

 increasing our list of imponderables. If these principles differ thus intrinsically from 

 one another, the question comes home to us, What are they? If electricity, and heat, 

 and light are three recognised imponderables, are not the tithonic rays a fourth, and the 

 phosphorogenic emanation a fifth ? 



995. In view of this, I would suggest the propriety of ceasing to call these last by 

 the epithet of emanations, and of giving them the more appropriate name of PHOSPHO- 

 ROGENIC RAYS. 



996. And now, what appears to become of M. BECQUEREL'S hypothesis, that all the 

 different effects we have been considering are due to light, and are presented to us 



