9 2 



Chemical and Physical Notes 



deep-sea thermometer is necessary, if we are to have the 

 conviction that the temperature indicated by it is in truth 

 the temperature of the water in which it was immersed. 

 This is all the more necessary because, in order to guard the 

 bulb of the thermometer against the squeezing effect of the 

 pressure of the column of water to which it is exposed when 

 in use, it is hermetically enclosed in an outside bulb, the 

 space between them being partially filled with mercury. This 

 extra bulb increases greatly the term of cooling of the thermo- 

 meter. The conditions are quite analogous to those regulating 



TABLE XV. Particulars of Calorimetric Air Thermometers 

 made of Lead Glass. 



the cooling of thermometers in air. The term is comparatively 

 long when the thermometer is immersed in still water and 

 kept motionless in it. When the water has relative motion 

 with regard to the thermometer the term is reduced in 

 proportion to that motion. 



For practical purposes we require to know how long we 

 must leave the thermometer at the particular depth in order 

 to be sure that it has taken the temperature of the water. 

 The experiments required in order to furnish this knowledge 

 are extremely simple. The principle is exactly the same as 



