1861.] on Electrical Quantity and Intensity, 339 



Ruhmkorff coil combined very high tension with considerable quantity, 

 and its physiological effects were therefore very violent. 



A frictional machine was exhibited by Mr. Varley, constructed 

 on a plan of Dr. Winter's ; the plate was of vulcanite, or vulcanized 

 India rubber, about three feet in diameter, excited by amalgam in the 

 usual way ; its peculiarity was a large and lofty wooden ring, with a 

 metallic rod in its interior, which, by its overshadowing inductive in- 

 fluence, increased the length of the sparks from six or seven inches to 

 nearly eighteen. 



The forces of electrical attraction and repulsion are sometimes 

 stated to vary as the square of the intensity, sometimes as the square 

 of the quantity, and sometimes as the square of the distance ; but it 

 was contended, that these effects were due to the circumstance that the 

 quantity usually varies in the same ratio as the tension, and as the dis- 

 tance ; and that all the phenomena were more rationally explained by 

 the assumption that electrical attraction and repulsion vary in the 

 simple ratio of the quantity and of the tension, and of the distance 

 inversely. 



The instances in which the quantity present is not simply depen- 

 dent on the tension, are those in which other electrified bodies are 

 present, which, by their inductive influence, affect the quantity present 

 in all bodies in their vicinity without necessarily affecting their 

 tension. An insulated cylinder was connected with the positive pole of 

 a DanielPs battery of 600 cells, its negative pole being connected with 

 the earth ; so that the cylinder was in a condition to give off" a powerful 

 and visible current to another wire connected with the ground ; in this 

 condition a positively electrified disc was approached to it, and by its 

 inductive influence was shown to render one end of the cylinder 

 electrically negative, so that a carrier ball applied to that end showed 

 it to have a negative charge, thus presenting the apparent paradox of 

 a negative electrified body giving off a positive current to the earth, or 

 vice versa. One end was negatively electrified, and the other end 

 positively, but the tension was the same everywhere. 



According to the ordinary way of regarding this class of phenomena, 

 it was usual to state that the ends of the cylinder acquired a state of 

 positive or negative intensity y or that they had their intensity changed : 

 it was contended that this gave an inaccurate idea of the real nature 

 of the change, and that the approach of an electrified body, how- 

 ever near or however violently it might be excited, could not in the 

 slightest degree affect the tension of a conducting body, which was in 

 connection with the earth : the only influence it could have would be 

 to alter the quantity in the second body, by driving a portion of 

 its electricity downwards to the earth. It might be assumed as a law 

 that the tension of the electricity in every part of a conducting body of 

 moderate dimensioiis was the same, notwithstanding the vicinity of other 

 electrified bodies. If a positively electrified body were brought near 

 an insulated conductor, the distribution of the electricity in the second 

 body was changed, and its whole tension was raised, but the tension 



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