240 



Mr. W. Crookes. 



[Dec. 16, 



tried up to a certain point, and then set aside. The data which these 

 experiments would have given are now required for the discussion of 

 some results on the viscosity of gases, which I hope to lay before the 

 Society in the course of a few weeks ; I have therefore completed 

 them so as to embody the results in the form of a short paper. 



An accurate thermometer with pretty open scale was enclosed in a 

 If inch glass globe, the bulb of the thermometer being in the centre, 

 and the stem being enclosed in the tube leading from the glass globe 

 to the pump. 



Experiments were tried in two ways : — 



I. The glass globe (at the various exhaustions) was immersed in 

 nearly boiling water, and when the temperature was stationary it was 

 taken out, wiped dry, and allowed to cool in the air, the number of 

 seconds occupied for each sink of 5° being noted. 



II. The globe was first brought to a uniform temperature in a 

 vessel of water at 25°, and was then suddenly plunged into a large 

 vessel of water at 65°. The bulk of hot water was such that the 

 temperature remained sensibly the same during the continuance of 

 each experiment. The number of seconds required for the ther- 

 mometer to rise from 25° to 50° was registered as in the first case. 



It was found that the second form of experiment gave the most 

 uniform results ; the method by cooling being less accurate, owing to 

 currents of air in the room, &c. 



The results are embodied in the following table : — 



(Rate of Heating from 25° to 50°.) 

 Table I. 



Pressure. 

 760 millims. 



1 millim. 



Temperature. 



25° 

 25 to 30 

 30 35 

 35 40 

 40 45 

 45 50 



25° 

 25 to 30 

 30 35 

 35 40 

 40 45 

 45 50 



Seconds occu- 

 pied in rising 

 each 5°. 





 15 

 18 

 22 

 27 

 39 





 20 

 23 

 25 

 34 

 48 



