176 



NATURE 



\_Ju7ie 24, 18S0 



ratio of increased pressure 104. The central spindle 

 relatively still shorter. At times only the terminals were 

 illuminated, but sometimes strata formed on the positive 

 terminal. Fig. 29 is another representation copied from 

 a drawing. 



Fig. 25.— Distance X 4, 3"6 inches, pressure 170-5 mm., 

 224,342 M, 6300 cells, current not measured. The central 

 spindle has decreased relatively still more. 



Fig. 34, Distance X 7, 6-3 inches, pressure 3 mm., 

 3947 M, 1200 cells, the bottom point positive current 

 0'03896 W, a splendid stratification, though somewhat 

 unsteady ; the figure partly copied from a photograph, 

 partly from drawings. It was thought at first that well- 

 defined strata would not be formed in a jar of such large 

 diameter with the quantity of current at disposal, but this 

 experiment shows that this conjecture was unfounded. 

 The negative glow completely fills the neck of the jar. 



Fig. 31. — Distance 6'3 inches, pressure 2'4 mm., 3158 

 M, 1200 cells, current o'02728 W, a very steady stratifica- 

 tion when the bottom point was positive ; this curious 

 stratification completely overlapped the whole surface of 

 the bottom point and the brass holder, as if pushed back 

 by a force emanating from the negative, the glow around 

 the negative completely filled the upper portion of the 

 jar. 



An inner tube was now inserted in the bell-jar in order 

 to ascertain whether the contraction of the space sur- 

 rounding the discharge would have any effect on the 

 production of strata. A number of holes had been drilled 

 in opposite sides of the tube, which is 8 inches long and 

 I 'S inch in diameter. These holes were drilled with the 

 object of straining very fine platinum wires across at 

 different heights for ascertaining the temperature of the 

 arc at these positions, but in the experiments about to be 

 described there were no wires. 



The bell -jar was refilled with hydrogen and ex- 

 hausted ; distance of points 6'3 inches, pressure 2 mm., 

 2,632 M, 2,400 cells ; when the top point was positive 

 there was a production of ordinary strata resembling 

 (Fig. 32). But when the bottom was positive a very 

 remarkable phenomenon was observed, namely, the pro- 

 trusion of strata through the small holes, ^th inch in 

 diameter, in the walls of the inner lube, this being acconv 

 panied by an overpouring of negative discharge above the 

 top of it (Fig. 33). It seemed as if the positive discharge 

 sought a complete neutralisation with negative electricity 

 beyond the confines of the tube, the area of which was too 

 small to permit of complete relief. The close confinement 

 of the discharge at the bottom end of the tube which rests 

 on the glass plate of the pump may account for the non- 

 oozing out of strata through the holes when the top point 

 was positive. 



Some gas let in, pressure 4 mm., 5,263 M, 2,400 cells, 

 current 0-15470 W, a well-defined stratification occurred 

 when the bottom point was negative, but no oozing out 

 through the holes in the tube. Fig. 32. 



In order to prosecute their experiments in a vessel of 

 still greater capacity, the authors had constructed a larger 

 jar with a neck at each end, or more properly speaking, 

 perhaps, a tube supported horizontally on ebonite crutches. 

 It is 37 inches long and 5];! inches in diameter, its cubical 

 content was found to be 14,435 cub. centims., or 3'8 times 

 that of the bell-jar employed in the experiments on the 

 electric arc. The tube is shown in Fig. 5. 



The experiments with this tube will necessarily occupy 

 a considerable period, partly on account of the long time 

 it takes to exhaust it after each set, partly on account of 

 the v.ariety of experiments it is intended to make with it ; 

 consequently they describe only a few of the first results 

 hitherto obtained. 



For Example in Air 

 Pressure 3 mm., 3,947 M, 6,300 cells. Two luminosi- 

 ties were formed, the ring negative being surrounded with 



a nebulosity which completely filled the end of the tube. 

 The tube glowed brilliantly with a blue fluorescent light, 

 which proved to have great actinic power. A dry-plate 

 photograph obtained in five seconds records a very curious 

 phenomenon, namely, that the outer boundary of the 



luminosity appears darker than the tube (Fig. 35). It is 

 to be remarked that while the discharge was reddish 

 (nitrogen), the fluorescence of the tube was blue ; the 

 effect appears to be due to the absorption of a portion 

 of the fluorescent light emanating from the back of the 



