402 Intelligence and Miscellaneous Articles. 



silk ribbon, or a column of oil. On the other hand, no electro- 

 dynamic effects are seen under these conditions, and it is not 

 evident a priori that the slow movement of electricity is subject to 

 the same laws as that which regulates electric currents. The object 

 of this memoir is to show that Ohm's law, which applies to a 

 constant current, applies also to the slow propagation of electricity 

 in cases in which the electric flow may be considered to be constant. 

 He has found that the mode of propagation is the same in both 

 cases, and that the results attained in studying the case of imperfect 

 conductors, throw great light on important questions in reference 

 to true currents. 



The instrument which serves to measure the tension is a gold- 

 leaf electroscope ; the separation of the leaves is determined by 

 means of a telescope and a scale. The author employs two different 

 methods for measuring the intensity of the electric flow. The 

 method of the duration of the flow consists in giving such a charge 

 to the electroscope that the gold leaves take a position A ; it is put 

 in communication with the ground by means of the conductor 

 through which the electricity flows, and the time t is measured 

 which elapses while the gold leaves pass from the position A to 

 another position B. Q being the quantity of electricity lost by the 



electroscope, — is the electric loss of the electroscope in the unit of 



time. The conductor is removed and the experiment is repeated, 



and rp is obtained, which is the electricity lost by the electroscope 



alone in the unit of time. Consequently Q( — J represents the 



intensity of the electric flow in the conductor employed. The 

 second method consists in employing a discharging electroscope 

 the gold-leaf of which comes in contact with a small copper ball 

 communicating with the ground. The conductor in which electricity 

 is propagated puts a reservoir of electricity in connexion with this 

 electroscope ; and the intensity of the flow may be obtained from the 

 number of its discharges in a given time. 



Some of the principal results only can be enumerated here. 



The intensity of the flow is inversely proportional to the length of 

 the conductors. — This law has been verified for cotton threads of 

 different lengths by both of the above methods. It only obtains 

 with exactitude where the electric loss in the thread is inconsiderable 

 in reference to the flow itself. Where this condition does not pre- 

 vail, the author has found that the loss is proportional to the square 

 of the length of the thread, as it ought to be from the law of tensions. 

 According to M. Gaugain, the following are the conditions to be 

 fulfilled in order to obtain results agreeing with Ohm's laws, — laws, 

 that is to say, which ought to apply to the case of a constant flow, 

 and a loss by the air which may be neglected : — 



1. A reservoir of great capacity must be added to the electroscope. 

 The author used a condenser. 



2. Feeble tensions must not be used, and the initial tension of 

 the electroscope must not differ by more than a few degrees. 



