132 Professor Tyndall [June 1, 



induction, where water is the conductor, whilst it is known to be 

 essential to the many, only because, when water is the electrolyte 

 employed, electrolytic conduction is essential to every case of 

 electrolytic action. 



[M. F.] 



WEEKLY EVENING MEETING, 



Friday, June 1. 



The Duke op Northumberland, K.G. F.R.S. President, 

 in the Chair. 



Professor Tyndall, F.R.S. 

 On the Currents of the Ley den Battery. 



In our conceptions and reasonings regarding the forces of nature 

 we perpetually make use of symbols, which, when they possess a 

 high representative value, we dignify with the name of theories. 

 We observe, for example, heat propagating itself through a bar of 

 metal, and help ourselves to a conception of the process by com- 

 paring it with water percolating through sand, or travelling by 

 capillary attraction through a lump of sugar. In some such way 

 • we arrive at what is called the material theory of heat. The thing 

 seen is thus applied to the interpretation of the thing unseen, and 

 the longing of the human mind to rest upon a satisfactory reason, is 

 in some measure satisfied. So also as regards the subject of the 

 present evening's discourse ; we are not content with the mere facts 

 of electricity ; we wish to look behind the fact, and prompted by 

 certain analogies we ascribe electrical phenomena to the action of a 

 peculiar fluid. Such conceptions have their advantages and their 

 disadvantages ; they afford peaceful lodging to the intellect for a 

 time, but they also circumscribe it ; and by and by, when the mind 

 has grown too large for its mansion, it often finds a difficulty in 

 breaking down the walls of what has become its prison instead of 

 its home. Thus, at the present day, the man who would cross the 

 bounds which at present limit our knowledge of electricity and 

 magnetism finds it a work of extreme difficulty to regard facts in 

 their simplicity, or to rid them of those hypothetical adornments 

 with which common consent has long invested them. 



But though such is the experience of the earnest student of 

 Natural Philosophy at the present — though he may be compelled to 

 refuse his assent to the prevalent theoretic notions, he may never- 



