284 



Drs. De La Rue and H. W. Miiller. 



[Nov, 20, 



disks to the striking distance at atmospheric pressure for the battery of 

 11,000 cells. Afterwards a less number of cells was connected with the 

 disks and the bell- jar gradually exhausted until the discharge occurred; 

 the height of the gauge was then read off. Then a less and less 

 number of cells was connected with the disks and the operation was 

 repeated. There was a gauge about 36 inches long attached to the 

 pump-plate in order to indicate the pressure beyond the range of the 

 gauges attached to the pumps. 



In air the discharge took place at ordinary atmospheric pressure 

 with 11,000 cells when the disks were 0*13 inch, 3*3 m.m. distant; and 

 with 600 cells at an average pressure of 10 m.m. 



In hydrogen it took place at atmospheric pressure with 11,000 cells 

 when the disks were 0*22 inch, 5*59 m.m. distant ; and with 600 cells 

 at an average of 14 m.m. pressure. 



In carbonic acid, at atmospheric pressure with 11,000 cells, when 

 the disks were 0*122 inch, 3*096 m.m. distant; and with 600 cells at 

 an average pressure of 5*2 m.m. 



The numbers obtained for air, hydrogen, and carbonic acid respec- 

 tively were plotted down on millimetre scale paper, the abscissee being 

 1 m.m. = 2,500 M> the ordinates 1 m.m. = 25 cells, and curves drawn 

 to give a mean of the several observations. These appeared to re- 

 semble hyperbolic curves so closely that true hyperbolic curves were 

 found partly by a geometric construction, partly by computation, 

 which would intersect the mean experimental curves in two points. 

 The results of experiment were again laid down on these new curves, 

 and it was found that they did not differ more from them than they 

 did from each other. 



The ratio of the transverse axis (pressure) to the conjugate axis 

 (potential) of the hyperbolas set out on the above-mentioned scale, 

 was — 



For air 0*9665 



., hydrogen . . . . . . . . 1*0170 



,, carbonic acid . . . . . . . . 1*0690 



The striking distances at atmospheric pressure for spherical surfaces 

 3 inches radius and 1*5 inch diameter, with various potentials, as 

 given in Part I, page 14, curve VIII, and at page 64, also those for 

 nearly flat surfaces in pages 19 and 64, were reduced to millimetres 

 distance and plotted down in the same way, but not on precisely the 

 same scale as the preceding curves for constant distance and various 

 pressures. Hyperbolic curves were also found which intersected the 

 experimental curves in two points. 



It was seen in the case of spherical surfaces, the result having been 

 obtained as the average of a great number of experiments, that the 

 hyperbola coincided closely with the observations, while for plane 



