260 On the Excitement of Voltaic Plates. 



instituted many experiments on the subject: — but I am not sa« 

 tisfied that he has demonstrated it. The species of demonstra- 

 tion to which I have been accustomed, has always carried to 

 niv mind a degree of conviction far more irresistible than any 

 thing I have ever seen written on the subject of an electric fluid. 

 1 cannot help thinking that the points which are here considered 

 as demmistrated, have been only very ingeniously supposed ; the 

 suppositions being grounded on their capability [if true) of ex- 

 plaining electrical phoenomena. I do not mean to argue that 

 thcv are not true ; it might be as difficult to prove their falsity 

 as their truth ; we all know on whom rests the onus proband}. 

 Admit them, and probably they will explain very agreeably a 

 number of important and interesting pheenomena: — Give to 

 Archimedes a point on which to rest the fulcrum of his lever, 

 and he moves the earth. 



Mr. De Luc also seems to think that the rejection of the idea of 

 an electric fluid, such as he has analysed and described, involves 

 the whole field of electricitv and galvanism in obscurity. Now 

 I cannot possibly conceive how pausing a little before we enter 

 into tlie mazes of hypothesis can liave such an effect ; at the 

 same time I am satisfied that by stepping too boldly into the 

 w ide field of speculation we endanger the interest and reputation 

 of science. I do not consider the remote causes of phasnomena 

 to be the objects of science ; but the generalization of the known 

 properties of bodies, and the discovery of those properties by 

 observation and experiment. Thus, I suppose the science of 

 physical astronomy complete, although the remote cause oi gra- 

 vitation remain for ever unknown ; and the science of pneumato- 

 logv has been carried to a high degree of perfection by those 

 authors who have made no reference to the essential qualities of 

 spirit; and I cannot perceive an absolute impossibility for all 

 pheenomena, termed electrical, whether they become evident in 

 our confined laboratories or in the great laboratory of Nature, 

 the universe, being generalized and arranged in the form of a 

 science, independent of any curious inquiries as to the existence 

 and nature of an electric Jlnid. However indispensable, it is 

 certainly not sufficient that the causes to which we refer phee- 

 nomena be capable of explaining them ; thev must be known to 

 have an existence, before they can be supposed to operate. 



" It is a dictate of common sense," says the excellent Reid, 

 " that the causes we assign of appearances ought to be real, 

 and not fictions of human imagination ; and it is likewise self- 

 evident, that such cJTiuses ought to be adequate to the eflfecls 

 which are conceived to be produced l)vthem." Impressed with 

 tliis opinion, I do not think it advisable to interweave with ex- 

 perimental facts and legitimate conclusions, hypothetical as- 

 sumptions. 



