278 



The author proposes to distinguish the terms tension and intensity, as 

 applied to electricity j expressing by the first, the actual elastic force 

 of a given quantity, accumulated in a given space ; and by the second, 

 the action of that part which is in a state of freedom, and which is in- 

 dicated by its effects on the electrometer. 



Experiments are next related, which were made for the purpose of 

 showing the incorrectness of the explanation of the above fact pro- 

 posed by Mr. Singer, namely, that it depends on the electrical action 

 of the atmosphere. In the transmission of electricity between con- 

 ductors placed at a distance, the quantity required to produce a dis- 

 charge is directly as the distance; and conversely, the distance is di- 

 rectly as the quantity. This distance will, therefore, be a measure of 

 the tension ; whereas the attractive force, as indicated by the elec- 

 trometer, is a measure of intensity only. Another conclusion deduced 

 from this train of reasoning is, that the resistance of the atmosphere 

 to the passage of electricity is not really greater through any one 

 discharging distance than through another, and is in no case greater 

 than the existing atmospheric pressure ; and it was found by direct 

 experiment, that the distance through which a given accumulation of 

 electricity could be discharged, is inversely as the density of the in- 

 terposed air. When this air preserved its density unaltered, the ele- 

 vation of its temperature produced no difference in its power of con- 

 trolling the escape of electricity ; hence it is concluded that heated 

 air is no otherwise a conductor of electricity, than in as much as it 

 has thereby become rarefied $ but heat applied to solid conductors 

 was found to diminish their conducting powers. 



The electrical capacities of conducting bodies of different shapes 

 was the subject of inquiry. In plates having the form of parallelo- 

 grams, the relative capacities, when the areas are constant, are in- 

 versely as the sum of the length and breadth ; and when this latter 

 sum is constant, the capacity is inversely as the area. The capacity 

 of a plane circle differs but little from that of a square having the 

 same area; nor does it make any difference if the plates be turned 

 into cylinders, or prisms with any number of sides ; and the capacity 

 of a sphere or cylinder is the same as that of a plane equal to it in 

 superficial extent. 



The author proceeds to investigate some laws relating to the action 

 of electricity, when resulting from induction ; and particularly that 

 of the relation between electrical attraction and distance ; adducing 

 experiments in confirmation of the former being in the inverse dupli- 

 cate ratio of the latter. The attraction actually exhibited between 

 two equal spheres, he considers as composed of a system of parallel 

 forces, operating in right lines between the homologous points of the 

 opposed hemisphere. The author concludes by various observations 

 on the transmission of electricity to bodies in vacuo, from which he 

 infers the fallacy of all explanations of the phenomena of electrical 

 repulsion, founded on the supposed action of the atmosphere. 



The reading of a paper, entitled, "On the Generation of the Mar- 

 supial Animals 5 with a Description of the impregnated Uterus of the. 



