68 Chemical and Physical Notes 



a temperature higher than that of boiling water at the 

 moment, and lower than that of its own boiling-point ; but 

 it is admitted that the boiling saline solution produces pure 

 steam which must be in contact with the solution which 

 produces it. If the steam so produced is at the temperature 

 at which it would be produced by pure water boiling under 

 the same conditions, then it must by contact cool some of the 

 solution below its boiling-point. But it has been shown that 

 pure steam in contact with a saline solution, the temperature 

 of which is ever so little below that of its boiling-point, is 

 condensed by it, and has its temperature raised by such con- 

 densation. But steam of a lower temperature than that of 

 the boiling solution cannot be both condensed and generated 

 under the same conditions. We see that it is condensed ; 

 therefore it cannot be liberated unless its temperature is at 

 least as high as that of the boiling solution. There is no 

 reason to suppose that it can be any higher ; therefore, the 

 temperature of the steam leaving a boiling saline solution is the 

 same as that of the boiling solution itself. 



Meteorological Observations and Instruments. 



Full instructions for installation of instruments, and for 

 methods of observation and recording, will be supplied with 

 the instruments. It is unnecessary to repeat them here. But 

 there are one or two points, seldom adequately insisted on in 

 meteorological instructions, which may here be recalled. 



Thermometers. With the thermometers of the Expedition 

 there will be supplied information as regards the position of 

 the point of melting ice and as regards the agreement of other 

 parts of the scale with the standard ; but it is safe to affirm 

 that no information will be supplied with regard to the thermal 

 mass of the thermometers, or the rapidity with which they 

 respond to changes of the temperature of the medium in 

 which they are placed. The Rate of Cooling, or its reciprocal, 

 the Term of Cooling, of a thermometer is as important a 

 constant as the position of the ice-point or the length of 

 a degree. The following considerations will show that the 



