380 



Mr. J. L. Hoo-o- on Friction 



dry the cylindrical electric heater was placed about the tube 

 C, and while the exhaustion proceeded the tube was raised 

 to a temperature of about 150° C. to hasten the removal of 



Fisr. 1. 



the gas present in large quantities in the pores of the char- 

 coal at atmospheric pressure, and which separates from the 

 charcoal rather slowly under reduced pressure if the tempe- 

 rature is kept low. When the mercury pump had been used 

 to secure a fairly high vacuum the other parts of the apparatus, 

 viz. the McLeod gauge, the viscosity apparatus, and the 

 connecting tubes were heated to about 150° C. for the purpose 

 of removing from the glass the occluded gases. After the 

 pumping had proceeded for some time under these conditions 

 the heater was removed from 0, and the Dewar vessel con- 

 taining liquid air was substituted for it, and the other part 

 of the apparatus was allowed to cool down. The charcoal 

 was allowed to absorb what it would at the temperature of 

 the liquid air. Altogether the liquid air was kept surrounding 

 the charcoal for about eighty hours, and from time to time 

 during this interval a measurement of the decrement I was 

 made. At first the diminution in the value of the decrement 



