TRANSACTIONS OF THE SECTIONS. 41 



On Symmetric Conductors, ami the construction of Li cjhtning -conductors 

 By Prof. Cn. V. Zekger*. 



It is an experiment very well known in physics, to place two insulated metallic 

 hemispheres in contact with an insulated sphere of brass. If the former he charged 

 with electricity and removed from the inner brass sphere, no trace of electricity is 

 found on its surface. The electricity is shown to be accumulated only ou the s"ur- 

 face of the outer spherical conductor, with equal tension at every point of that 

 surface. 



The author shows that if the outer hemispheres be replaced by two circular 

 wires, no action whatever will be found ou the inner conductor. This fact may be 

 best illustrated by the apparatus shown, which consisted of a very sensitive electro- 

 scope placed on a brass plate, supported by a well-insidated stand. If a charged 

 ebonite rod be brought near to the electroscope when protected by two circular 

 wires placed round it, in such a manner as to be in connexion with its gold leaves, 

 or even if it is brought into contact with the ball of the electroscope, there is no 

 action upon the leaves; and if the electrified rod be brought between the two 

 wires and the electroscope itself, only a small action is observed. The author has 

 tried this experiment with a powerful electric machine (a Holtz machine), and 

 finally with a large induction-coil of Kuhmkorlf ; and the result was, that sparks 

 of 35 centims. length produced no effect ou the electroscope. 



At the request of M. Faye, Ruhmkorff made similar experiments with his largest 

 electric machines, putting a workman in the space between the protecting wfres. 

 There was no sensation of electric shocks on using the most powerful electric 

 machine, though a shock was felt on the head of a workmnn when a large induc- 

 tion-coil was used. The author showed that the effect produced by the action of 

 the pointed needle,^ though greatly diminished by the wires, is yet sensible, and 

 that in Ruhmkorfi's experiment a discharge produced by the interference of a 

 pointed body may account for the diflerence observed by him. 



It is easy to see that this experiment may prove useful in regard to the construc- 

 tion of electric apparatus and of lightning-conductors. The author, therefore, has 

 examined the action of other forms of symmetrically-arranged conductors. In the 

 first instance he tried parabolic wires, joined in the same manner to the electroscope 

 to be protected from the action of electricity, with the same effect; next rect- 

 angular wires. If the electroscope is placed exactly in the middle of the rectangular 

 wire, no action is observed; placing it excentrically, there is small but increasing 

 action, at least if electric sparks of great intensity are striking the ball of the elec- 

 troscope. _ If a needle or any other sharp -pointed body is placed between the pro- 

 tecting wire and the electroscope, it is easy to observe the different actions produced 

 by placing the electroscope in an excentrical position. 



Symmetrical wires placed on buildings or over entire cities in this way, would 

 probably give complete protection from atmospheric electricity ; for if the electric 

 clouds were even to enter between the objects protected and the protecting vrires, 

 their activity would be gi-eatly diminished, as shown by the experiments described; 

 for the wires would become immediately charged, and nearly all the electricity 

 would be accumulated on their surface, without any danger to the protected build- 

 ings of being struck by lightning. 



Meteobology &c. 



On the Undercurrents of the Bosphorus and Dardanelles. 

 By William B. Caepenter, MD., LL.D., F.R.S. 



In continuation of his communication last year on the Gibraltar Undercurrent 

 and General Oceanic Circulation, Dr. Carpenter gave the following summary of the 

 results of the experiments recently made, under direction from the Admiralty by 

 Capt. Wharton of H.M.S. ' Shearwater,' to put to the test the correctness of I)r. 

 * Vide Comptes Eendus de I'Academie des Sciences ,Sept. 8, 1872; Le Monde, Sept. 1872. 



