6 



AßT. 12. — H. HIEOBE : ON THE FÜÖIO:^ SURFACES OF THE 



B. 



The Measurement of Tem-peraiure. 



All temperatures were measured with a tliermo-element of 

 iron and nickeliue. The fixed temperature was maintained by a 

 thermostat at 25°. 



The temperature of a thermostat is subject to irregular local 

 fluctuations, which are not usually in- 

 dicated by the thermometer placed in it, 

 because an ordinary mercury thermometer 

 reacts too slowly. But this may affect 

 the thermo-element whose indication is 

 much quicker. As the disturbance is due 

 to the current of water it can be easily 

 removed. Fig. 2 h is a glass vessel with 

 a cork, through two holes in which the 

 thermometer d and one of the junctions 

 c of the thermo-element are inserted, e is 

 a wide glass tube put around the thermo- 

 meter. The water of the thermostat is 

 sucked up into it and kept at the proper 

 level by means of a ])inch cock. In this 

 way the water circulates by convection, 

 and it may be assumed that the whole 

 mercury thread of the thermometer is at 

 the temperature of the thermostat. The 

 glass vessel dipped in the thermostat 

 hinders the communication of the water 

 with the outside and the small local 

 variation in the temperature of the thermo- 



Fiu-. 2. 



stat has little influence upon the interior of the vessel. Tl 



uis 



