282 



Dm De La Rue and H. W. Miiller. [Nov. 20 



a table previonsly calculated, the value of the deflection in ohms of 

 resistance per cell could be read off; this multiplied by 11,000 gave 

 the total resistance of the battery ; the tube was then connected with 

 the terminals and the galvanometer again observed ; this gave a less 

 deflection and indicated a greater resistance, which, multiplied by 

 11,000, gave the total resistance of the tube and battery : by sub- 

 tracting the resistance of the battery the resistance of the tube was 

 ascertained. Calling the total resistance R, the tube resistance ?*, the 



tube-potential V, V— r X The tube-potential requisite to pro- 



R 



duce a discharge, with a pressure of 46,710 M, was found to be 

 10,250 cells; this gradually fell until a pressure of 0*642 m.m., 

 1,082 M- was reached, the tube-potential being then only 430 cells, 

 after which it rapidly rose and, at 8"6 M, it required a potential 

 of 8,937 cells to produce a discharge. From the experiments de- 

 scribed in Part II (p. 103, foot note), it was found that, in another 

 tube, it required the full potential of 11,000 cells to produce a dis- 

 charge at 3 M, and that, at 1*8 M, this potential was insufficient. 

 The obstruction to the discharge in tube 162 was as great at 8*6 M, as 

 at 28,553 M pressure, and required 8,950 cells in each case. A few of 

 the more remarkable phases of stratification in tube 162 are shown in 

 one of the plates which illustrate the paper. 



The next part of the paper deals with the potential necessary to 

 produce a discharge between disks 1*5 inch in diameter, at a constant 

 distance and at various pressures. 



In the first instance, an experiment was made in order to ascertain 

 whether there was either any condensation or dilatation of the gas 

 in contiguity with the terminals before the actual passage of the dis- 

 charge. In order to do this an apparatus was constructed, as shown 

 in fig. 1. 



It consists of a glass cylinder, the depth of which is accurately the 

 same in every part, so as to ensure the parallelism of two glass disks 

 which close its ends. 



These are held in contact with the ends of the cylinder by means of 

 screw-clamps made of ebonite, and the whole apparatus is supported 

 on a tripod ebonite stand, which is fastened to a square wooden foot. 

 Attached parallel to the top and bottom glass disks, by means of 

 flanged- screw rods, are two brass disks with rounded edges, 4 inches 

 in diameter; these are maintained at a distance of 0*13 inch, 3'3 m.m., 

 at which the discharge of 11,000 cells would only just take place. 



The ends 'which project through the glass disks are furnished with 

 binding-screws for attaching wires from the battery. 



On the side of the cylinder is a tubulure in which is fitted a gauge 

 containing strong sulphuric acid, so as to dry the inside of the ap- 

 paratus, and to indicate whether any condensation or dilatation of the 



