Conduction of Heat in Liquids. 7 



liquid is introduced between the two glasses, the interval be- 

 tween which can communicate with the exterior by a small 

 lateral aperture, some distance below the junctions of the 

 glasses but above a fixed level, to which the enclosed liquid is 

 brought. In the mouth of the inner glass is a cork holding- 

 fast the stem of a thermometer with a long bulb. The inner 

 glass is filled with mercury up to a fixed level slightly lower 

 than the level of the liquid to be examined, and the thermo- 

 meter is fixed so that its entire bulb is surrounded by the 

 mercury. The distance between the curved surfaces of the 

 glasses is small compared to the radius of the inner glass, 

 which in turn is small compared to the length of the glasses 

 or of the bulb of the thermometer. Thus fairly good results 

 may be expected from a mathematical treatment which regards 

 the liquid as existing between two infinite circular cylinders. 

 Beetz's main observations consist of two series, one at a low, 

 the other at a higher temperature. In the former the whole 

 apparatus was immersed in an ice-bath and removed when the 

 enclosed thermometer indicated 1° C. It was then wiped dry, 

 and, on the thermometer indicating 2°, plunged into a bath 

 of water at 20°. The bath was kept full to the top, so that 

 the apparatus was always immersed to the same depth. The 

 moment when the thermometer indicated 4° was taken as a 

 starting-point, and the times of rising successive intervals of 

 2° carefully noted. In the second series the apparatus was 

 immersed in a water-bath of over 45°, and at 44° plunged 

 into the water-bath of 20°, the times of cooling successive 

 intervals of 2° being reckoned from the moment when the 

 thermometer stood at 40°. For the velocity v of cooling or 

 heating, Beetz assumed the formula 



vt= log(T /r); 



where t is the difference between the temperatures of the 

 enclosed thermometer and the bath at the instant from which 

 the time is reckoned, whilst t is the difference at time t. He 

 supposed the conductivity of the liquid to be proportional to 

 a quantity C given by 10~ 5 G = v\oge. He found that the 

 above formula did not apply to the interval immediately sub- 

 sequent to the immersion of the apparatus, and that towards 

 the end of the experiment it again failed. For the intervals 

 corresponding to the limiting values 6°-14° in the first series 

 of experiments, and 36°-28° in the second, it answered very 

 well. The discrepancy in the later stage of the experiment 

 seemed due to the gradual collection round the apparatus of a 

 layer of water differing in temperature from the rest of the 

 bath. 



