1877.] 



the Chloride-of- Silver Battery. 



521 



on the disk was 30,000 grains with the point negative, and 18,000 grains 

 when it was positive : to reproduce these strains the paper had to be 

 loaded with 129,600 and 53,530 grains respectively after the current had 

 been shut off. 



"When terminals with plane or spherical surfaces are used, the luminous 

 phenomena preceding the jump of the spark do not take place, and there 

 is scarcely an appreciable adherence between the band of paper and the 

 terminals ; it generally takes a diagonal position, forming a bridge between 

 them. 



Between a point and a disk the spark is longest with the point positive, 

 when. from 5000 to 8000 cells are used; but for a less number of ele- 

 ments, 1000 to 3000, it is longest when the point is negative. 



The length of the spark is greatly influenced by the form of the point : 

 thus with a point in the form of a cone of 20 degrees the striking- distance 

 is 0*184 inch with 5640 ceils and 0*267 inch with 8040; while with a 

 point approaching a paraboloid in form, and with the same base and of 

 the same height as the cone, it is 0*237 inch with 5640 cells and 0*343 



inch with 8040. The ratios ^=0*776 and ?^ = 0*778, almost iden- 



237 343 



tical, represent the proportion which exists between the length of spark 



obtained with a conical point and one paraboloidal in form. 



The striking-distance between a point and a plate is in accordance, 



very nearly, with the hypothesis of this distance increasing in the direct 



ratio of the square of the number of elements, at all events up to 8040 



cells, thus *: — 



Number of cells... 1000 2000 3000 4000 5000 6000 7000 8000 



in. in. in. in. in. in. in. in. 

 Distance observed... 0-0051 0-0221 0*0554 0*103 0*159 0*222 0*286 0*352 

 Distance calculated 0-0055 0-0220 0*0495 0*088 01375 0*198 0*2695 0*352 



Between plane, spherical, or cylindrical surfaces the striking-distance 

 does not follow this law ; on the contrary, the increase is nearly, but not 

 quite, in the ratio of the number of cells. "We have given the striking- 

 distance from 1000 to 8000 volts, between spherical surfaces 1*5 inch 

 diameter and 3 inches radius, in the Proceedings, No. 182, so that it is only 

 necessary here to state the striking-distance for 



1000 cells. 8000 ceUs. 



in. in. 



Between spherical surfaces 0*0050 0*0810 



plane surfaces 0*0104 0*0852 



„ two concentric cylinders . 0*0071 0*0991 



It must, however, be stated that very probably the striking-distance 

 for 1000 cells between plane surfaces is too great, on account of the diffi- 

 * Proc. Roy. Soc. 1876, vol. xxiv. p. 167. 



