2 Mr. W. R. Grove on a Method of increasing 



four cells of 2 inches by 4 of the nitric acid battery be used, 

 and a pint Leyden phial, but little increase of effect will be 

 obtained by u*iug eight or more cells, and the platinum at the 

 contact breaker would be rapidly destroyed by the sparks. 



But substitute for tbe pint Leyden phial one of double the 

 capacity, and it will be found, that though this second phial was 

 inferior to the first with a battery of four cells (giving shorter 

 sparks, and fewer in a given time, though somewhat denser), 

 yet it is far superior to the first witli the battery of eight cells, 

 and the sparks at the contact breaker are no longer injurious. 



By adding more coated surface, for instance, another phial, 

 four more cells may be added, and increased effects will be ob- 

 tained, and thus with the same coil the brilliancy of the discharge 

 may be increased to an extent to which I have not yet found a 

 limit. I obtained this result some months back ; but not having 

 a large battery, I did not go beyond ten cells, which I found 

 would well bear a jar of one square foot coated surface. 



By the aid of Mr. Gassiot's more powerful apparatus, I have, 

 with him, used thirty cells of the nitric acid battery, 2 inches 

 by 4, and five square feet of coated surface ; the effects were very 

 striking, — a roar of voluminous discharge of 06 of an inch long, 

 increased to 1*3 inch when the flame of a spirit-lamp was placed 

 between the terminals. I have never witnessed such a torrent 

 of electrical discharges ; the noise could not be borne long with- 

 out great discomfort. 



With the same voltaic battery, and an additional square foot 

 of coated surface, the effect was somewhat diminished. Mr. Gas- 

 siot had not more than thirty cells available at the time of our 

 experiments, so that I have not yet ascertained the limit to which 

 this increase of power can be carried. I presume, however, there 

 is a limit, for reasons which will be presently apparent. 



The following precautions are essential to the success of the 

 experiment : — 



1st. The wire proceeding from the outer extremity of the 

 secondary coil must be connected with the inside or insulated 

 coating of the Leyden battery, if the battery is not wholly insu- 

 lated. The reason of this is, that the outer extremity of the coil 

 is the better insulated portion, and also that to which electricity 

 of tension flies off; a good spark can, under ordinary circum- 

 stances, be obtained from the outer, but scarcely any from the 

 inner terminal of the coil. 



2nd. The distance between the hammer of the contact breaker 

 and the soft iron core should be made as great as practicable, 

 at least one-eighth of an inch ; this is an important point as to 

 the theory and experimental results of the Ruhmkorff coil. 

 Time, as is well known, is necessary for the development of 



