194 Dr. M. Smoluchowski de Smolan 



on 



Then we have still conduction and radiation. These two 

 can be separated by comparing experiments got with vessels 

 of different sizes (Winkelmann) , or by measuring the effect 

 of radiation by itself, when the best possible vacuum has 

 been made (Kundt and Warburg). 



In the experiments described below both of these methods 

 were used. 



4. The experimental arrangement was quite similar to 

 that of Mr. Brush (and others before) : but the shape and 

 dimensions of the thermometer and the glass vessel were 

 adapted to my special purpose. 



The thermometer BT (see figs. 1 and 2) had a cylindrical 

 mercury-bulb B and a very thin stem S, thickened in the 

 middle in the shape of a stopper F, so as to fit air-tight 

 in the mouth of either of two cylindrical glass vessels, 

 Vi and V n , formed alike, and differing only in the value 

 of the diameter. The outer diameter of the mercury-bulb 

 was r= 0*4566 cm., its length Z= 6*57 cm. ; the inner dia- 

 meter of vessel I. 11=0*653 cm., of vessel II. R= 1*573 cm. 

 These vessels were connected by glass tubing with a mercury 

 air-pump (Topler's construction), which was adapted also to 

 the measurement of low gas-pressures by an arrangement 

 similar to McLeod's gauge. (See Bessel-Hagen, Wied. Ann. 

 xii. p. 434.) 



Greatest care was taken for dryness of the pump and 

 apparatus, and for the air-tight fitting — by means of some 

 mercury poured in — at the mouth M and at the stopcock C. 



The mode of experimenting was quite simple. When the 

 gas was brought to the desired density, the vessel, with 

 the thermometer in, w r as heated by hot w r ater to nearly 

 100° C. ; then it was suddenly immersed in ice, and now 

 the cooling-down of the thermometer w r as observed by 

 measuring the time which the mercury column took for 

 creeping back from the point 100 of the scale to the zero- 

 point (corresponding in reality to the temperatures 47°*99 

 and20°*04C). 



5. Let us consider now in what way we might be able to 

 decide, by observing the time of cooling, whether there is any 

 such discontinuity of temperature between the gas and the 

 solid, or not. 



If we denote by C the caloric capacity of the thermometer- 

 bulb, by <rS the quantity of heat radiated from its surface to 

 the sides of the glass vessel, and by tcJj the quantity con- 

 ducted in the same way through the gas, when there is 

 a difference of one degree between them, the temperature 6 

 of the thermometer-bulb (which, approximately, can be 



