468 



Royal Society :- 



normal pressure of the atmosphere to 0*112. It now begins to 

 fall off : at 200 millionths it is 0*110, at 100 millionths it is 0*096, 

 at 50 millionths it is 0*078, at 20 millionths it is 0*052, at 10 

 milliouths it is 0*035 ; and at 0*1 of a millionth of an atmosphere 



the log. dec. has fallen to about 0*01. Simultaneously with this de- 

 crease in the viscosity,[the force of repulsion exerted on a black sur- 

 face by a standard light varies. It increases very slowly till the 

 exhaustion has risen to about 70 millionths of an atmosphere ; at 

 about 40 millionths the force is at its maximum ; and it then sinks 

 very rapidly, till at 0*1 millionth of an atmosphere it is less than one 

 tenth of its maximum. On continuing the curves of the log. dec. and 

 the force of radiation, and assuming that the torsion-fibre of glass 

 has no viscosity, it is most probable that they both would come 

 to zero when the last traces of an atmosphere 'had been taken out 

 of the apparatus. 



The oxygen diagram differs from that of air. The log. dec. is 

 0»126 at the atmospheric pressure; it falls to 0*111 at a pressure 



