450 



Mr. W. Crookes. 



[Feb. 17,. 



Experiments are next described on the resistance of air to the passage 

 of an induction spark. 



Since the publication of the author's researches on the phenomena 

 presented by the passage of the induction discharge through high 

 vacua, the present results — which, although never published, precede 

 by a year or two those just mentioned — have lost much of their 

 interest. 



The phenomena at the very high exhaustion of 0*02 M may be of 

 interest. With a coil giving a spark 85 millims. long, no discharge 

 whatever passes. On increasing the battery power till the striking 

 distance in air was 100 millims. the spark occasionally passed through 

 as an intermittent flash, bringing out faint green phosphorescence on 

 the glass round the end of the — pole. 



On one occasion the author obtained a much higher exhaustion than 

 0'02 M. It could not be measured, but from the repulsion by radia- 

 tion and the low log decrement it was probably about 0*01 M. The 

 terminals of the vacuum tube and wires leading to them were well 

 insulated, and the full power of a coil giving a 20-inch spark was put 

 on to it. At first nothing was to be seen. Then a brilliant green 

 light flashed through the tube, getting more and more frequent. Sud- 

 denly a spark passed from a wire to the glass tube, and broke it, ter- 

 minating the experiment. 



Since these experiments, vacua have frequently been got as high, 

 and even higher, but the author has never seen one that would long 

 resist the 20-inch spark from his large coil. % 



Viscosity of Oxygen. 



The series of experiments with air show a complete history of its 

 behaviour between very wide limits of pressure. It became interest- 

 ing to see how the two components of air, oxygen and nitrogen, would 

 behave under similar circumstances. Experiments were therefore insti- 

 tuted exactly as in the case of dry air, but with the apparatus filled 

 with pure oxygen. 



The results are given in the form of tables and plotted as curves on 

 diagrams. 



The figures show a great similarity to the air curve. Like it the 

 log decrement sinks somewhat rapidly between pressures from 

 760 millims. to about 75 millims. It then remains almost steady, not 

 varying much till a pressure of 16 millims. is reached. Here, how- 

 ever, it turns in the opposite direction, and increases up to 1*5 millim. 

 It then diminishes again, and at higher exhaustions it rapidly sinks. 

 This increase of viscosity at pressures of a few millimetres has been 

 observed in other gases, but only to so small an extent as to be 

 scarcely beyond the limits of experimental error. In the case o£ 



