198 Dr. M. Smoluchowski de Smolan on 



Air in Vessel II. 



t 311 380 380-2* 383-7 3985 443-9 509-8 628-2 698'7 



p 770 211 379 1-72 0-34 0086 0033 0-010 0-0043 



K 1-00 0-983 0-917 0736 0-524 0249 0126 



y 000734 00398 0158 0-398 1-33 304 



1 1-66 1-78 1-78 1-72 1-83 (1'73) 



A 



Similar experiments were made with hydrogen. 



The bracketed values are not to be relied upon, as a con- 

 siderable source of error arises in them from the vapour- 

 pressure of mercury ; also the theory, exposed later on, is 

 not quite justified for them, as the free path of molecules 

 is too great ; nevertheless they agree very well with the 

 other values. 



7. The observations are sufficient to justify the following 

 conclusions : — 



(1) If the convection-currents were producing any sensible 

 effect, the time of cooling would have shown a marked increase 

 when the pressure began to decrease down from 1 atmo ; 

 but neither hydrogen nor air in the smaller vessel (I.) shows 

 any appreciable influence of pressure between 760 and about 

 50 mm.; with air in the wider vessel (II.) an increase of 

 cooling time can be noticed from 760 to 210 mm.; then it 

 remains constant to about 40 mm.; it is this value (marked 

 with an asterisk) which was supposed to be due to pure con- 

 duction and radiation. 



(2) For eliminating the effect of radiation, it was supposed 

 that in the best possible vacuum obtained there was no longer 

 conduction of heat, only radiation. This assumption is 

 supported by the fact that the time of cooling, which at 

 normal higher pressures was 37 resp. 94 sec. for hydrogen, 

 and 184 resp. 380 sec. for air, appeared to be 790 sec. in the 

 vacuum, independent of the size of the vessel used and of the 

 nature of the gas with which it had been filled. It was 

 increased to 6807 sec. by roughly silvering the thermometer- 

 bulb. 



Also the second method of eliminating the radiation, by 

 applying the formulae (4) and (2) to corresponding measure- 

 ments at normal higher pressures in both vessels (of known 

 dimensions), gives well agreeing results. 



(3) The increase of the time of cooling at pressures below 

 several millimetres of mercury cannot be due to a diminution 

 of the coefficient of conductivity, which ought to be the same 

 for both vessels at corresponding densities, because the 

 apparent conductivity (as shown by the values of K) varies 



