116 Professor Low's Remarks on the Review of his 



on which it is received? To go no further in a discussion 

 which has ah'eady extended this paper too much, if the agent 

 is the same in all cases, and the difference perceived is due to 

 the receiving surface, how is it that a ray of light which has 

 passed through a piece of transparent glass can no longer 

 excite phosphorescence in the sulphuret of lime ? Can we 

 escape the conclusion that the ray has had something removed 

 from it, or has had some modification impressed on it, or, in 

 short, that something invisible to the eye has been taken away? 



To my mind these considerations are conclusive, and 1 

 therefore regard the tithonic rays as constitutiyig a fourth im- 

 •ponderahle, and the phosphorogenic rays as a fifth. 



University of New York, 

 April 12, 1844. 



XVI. Remarks on the Review of a work entitled^ " An Intjuiry 

 into the Nature of the Simple Bodies of Chemistry," in- 

 serted in the Philosophical Magazine for Api'il 1844. By 

 David Low, Esq.^ F.R.S.E.y Professor of Agricidture in the 

 University of Edinburgh. 



To Sir David Brewster^ K.H., Sfc. S^c. Sfc. 

 Dear Sir, 

 A LTHOUGH I have not the pleasure of a personal ac- 

 -^^ quaintance with you, I will venture to address you as if 

 I had, on the subject on which I am now to trouble you. 



I send you a little work published about six months ago, 

 together with the April Number of the Philosophical Magazine, 

 in which a criticism on the work appears. I call it a criticism, 

 but you will perceive that it is nothing but an attack, and a 

 very virulent one, on the author. 



An opinion entertained by many chemists, it is well known, 

 is, that the simple bodies of chemistry, so called, are not 

 really simple, or that they can only be termed simple with re- 

 lation to the present state of our knowledge and our means of 

 analysis. I have ventured to enunciate the proposition some- 

 what more precisely, and endeavoured to prove that these 

 bodies cannot be separated in their nature and functions from 

 the great class of bodies which we know to be compound. 

 Thus chlorine cannot be separated as one of a distinct order 

 of natural bodies from cyanogen, with which it exhibits the 

 closest parallelism in its chemical actions and relations. 



To establish and illustrate my argument, I have ventured 

 to inquire whether we cannot reasonably suppose the simple 

 bodies, so called, to be resolvable into other bodies of the 

 same class. I assume, in the first place, that all these bodies 

 may be resolved into three, hydrogen, carbon and oxygen, 



