291 



chemical action at one pair of plates cannot pass by another pair ex- 

 cept an equal chemical action take place there ; and as the chemical 

 and electrical action are always equivalent, the equal chemical action 

 at the second pair will do no more than suffice to transfer forwards the 

 forces disturbed at the first pair, and can add nothing to their quan- 

 tity : but they can add to their intensity, and in fact the recurrence 

 of a second chemical action at the second pair of plates has exactly 

 the same effect as would be produced by a more intense chemical ac- 

 tion at the first pair. In this way it is that numbers of plates give 

 energy to the voltaic pile, and enable its power to penetrate elec- 

 trolytic bodies and permeate bad conductors in a manner which could 

 not be done by the electricity of a few pairs of plates only. 



The fourth part of the paper relates to the resistance opposed to 

 the electric current at the place of decomposition, and refers this at 

 once to the resistance of the chemical affinity which has to be over- 

 come. This of course varies with the number of places where de- 

 composition is effected, the strength of the affinity of the elements of 

 the decomposing body for each other, and the nature of the substance 

 against which the decomposition is effected, and by which it may very 

 frequently be assisted. All these are taken into account, their ge- 

 neral, and occasionally particular, results shown, and their perfect 

 harmony with the principles previously advanced pointed out. 



In the last part of the paper some general remarks on the active 

 voltaic battery are made, in which the influence of several distinct 

 causes in producing a rapid change and deterioration of action is 

 pointed out. Each of these causes is considered separately, and the 

 effects they produce are shown to be necessary consequences of the 

 principles already laid down as those of the voltaic battery. 



The following Papers were then read : 



1. " Observations on the Teredo navalis and Limnoria terebrans, as 

 at present existing in certain localities of the British Islands." By 

 William Thompson, Esq., Vice-President of the Natural History 

 Society of Belfast. Communicated by J. G. Children, Esq. Sec. U.S. 



The opinion which has been advanced, that the Teredo navalis is 

 no longer to be found on the British coast, is shown by the author to 

 be erroneous ; for numerous specimens of that destructive animal, 

 collected from the piles used in the formation of the pier at Port- 

 patrick in Ayrshire, were furnished to him by Captain Frayer, R.N. 

 (of His Majesty's Steam-packet Spitfire). Some of these specimens 

 had attained the length of nearly two feet and a half, a magnitude at 

 least equal to, if not exceeding, the largest brought from the Indian 

 seas. After giving a description of the animal, the author enters into 

 an inquiry into the agency it employs to perforate the timber which 

 it consumes as food, and in which it establishes its habitation. He 

 ascribes tonne action of a solvent, applied by the proboscis, the smooth 

 and rounded termination of its cell, which is afterwards enlarged by 

 the mechanical action of the primary valves. 



The author then gives an account of the natural history and opera- 



