M. Cahours on Acetosalicyle. 299 



portion to the size of the machine must be very considerable; 

 and the only advantage which they appear to possess as a com- 

 pensation for this loss, is that of affording very long sparks from 

 a large conductor. 



The cause of this difference in the exciting power of plates 

 and cylinders is not to me perfectly clear. It is possible that 

 the difference in the chemical composition of plate- and flint-glass, 

 as well as the difference in the mechanical character of their sur- 

 faces, the latter being a surface of fusion and the former a ground 

 and polished surface, may have some influence over their electric 

 capabilities. There is also another peculiarity to which I have 

 before alluded in connexion with plate- and crown-glass, viz. their 

 retentiveness of the electric charge, which may operate as preju- 

 dicially to the free action of electricity excited on its surface, as 

 it does to the free action of a charge communicated by metal 

 coatings when used in the form of a Ley den jar or coated plate. 

 I am more inclined, however, to believe that the cylinder owes 

 its superiority to the fac£ that the electrical excitation of the in- 

 terior consequent on the friction of the exterior, is incapable of 

 exercising any controlling inductive action internally, every por- 

 tion of this inner surface being diametrically opposed to another 

 portion similarly electrified. 



The whole of the action is thus determined to the external 

 surface, as is the case with an electrified hollow metal cylinder 

 or sphere, which exhibits scarcely any electrical effects in the 

 interior, though its outer surface appears highly charged. This 

 is not the case with the plate, both of whose surfaces are freely 

 induced upon by surrounding objects. 



Any amount of electrical excitation therefore on one side of 

 the plate will require, for the full development of its free action, 

 an equal amount of excitation of the same kind on the other 

 side, in order to compensate for the controlling action of vicinal 

 inducing bodies. Since, however, this will only account for the 

 loss of one-half of the power, there' remains still another source 

 of equal loss to be discovered; for, admitting upon this principle 

 of compensation that two rubbers are necessary in order to 

 obtain the full ( ffect of one, we still by no means account for the 

 fact that the cjuantity actually developed by one pair of rubbers, 

 is only half of what it should be as compared with a cylinder. 



XXXVII. Chemical Notices from Foreign Journals. 



By E. Atkinson, Ph.D. 



[Continued from p. 11 7-] 



COUMARIC acid, C'^ U^ Q*', stands to hydride of salicyle, 

 Qij j[G Q4^ i,i tij(. same relation as does cinnamic acid, 

 C'« IP 0", to hydride of bcnzoylc, C" IP' 0^. I3oth acids expc- 



