Mr. M. Roberts on the Electric and Nervous Influences. 31 



inserted in the address delivered at the first annual meeting 

 of the Geological Society of Dublin by their President, I then 

 extracted from my memoir on the East of Ireland certain 

 details, in which the occurrence of tin ore in connexion with 

 native gold in both Croghan Kinshela and Croghan Moira 

 mountains is again mentioned. 



We have it thus four times in evidence in print, dating 

 from the year 1801 to 1835, that tin ore does occur in Ire- 

 land, to which Dr. Smith's testimony in 1840 now adds a 

 fifth ; and this independently of what may be found in the 

 printed proceedings of the Dublin Society in the early part 

 of this century. But it follows from the preceding, that Dr. 

 Smith, in his examination of the washed sand lately procured 

 from Croghan Kinshela mountain, has not elicited a single 

 fact that was not established and known more than forty 

 years since. 



V. On the Analogy between the Phcenomena of the Electric and 

 Nervous Influences. By M artyn Roberts, Esq., F.R.S. Ed.* 

 1. \ LTHOUGH much has been said by eminent physio- 

 ■^"*- logists in endeavouring to prove that an essential dif- 

 ference exists between the nervous and the electric power, 

 yet there are so many points of analogy untouched by these 

 writers, and the facts they have adduced are so susceptible of 

 explanation by electrical laws, that I feel convinced there is 

 the greatest similarity, if not identity, between the nervous 

 and electric influence, both in their mode of action and in the 

 phenomena produced. 



2. In the first place, I may call attention to a beautiful ana- 

 logy which has, I believe, hitherto escaped observation, viz. 

 the influence of electricity on the circulation of fluids ; and 

 there is just cause for believing that a like influence governs 

 the circulation of the blood in the living body. 



3. If we calculate the force of the heart, we shall find it 

 wholly inadequate to propel the blood through the fine capil- 

 lary vessels of the system, unless it be assisted by some other 

 power. There are two sources of resistance to the motion of 

 fluids in tubes, at least two that especially apply to the motion 

 of the blood through the vascular system, viz. the tortuosities 

 of the tubes, and the adhesion of blood to the sides of the chan- 

 nel through which it is impelled. 



4. The resistance occasioned by the deviation of a channel 

 from a straight line is easily overcome when the motion of the 

 fluid in it is slow ; for this resistance is the destruction of the 

 momentum, or tendency of the fluid to move in straight lines, 



* Communicated by the Author. 



