104 



MR. W. N. SHAW OX HYGROMETEIC MKTHODS. 



The theoretical dew-point is taken from the temperature of the saturator, but the 

 observations included in the table are only those for which the result of the chemical 

 method agreed very closely with that of the saturator. 



It will be seen that the differences are most frequently negative. They are 

 generally very small, so that it would appear that the assumptions specified on p. 101 

 are generally justified by the experiments. There are two cases in which the dew- 

 point is considerably below the saturator temperature, namely, Nos. 53 and 55. I 

 quote the observations for these two experiments : 



No. 53. 



If in this case we take the last three readings only, we get- 

 Mean temperature of saturator . . 3'47 

 Correction '23 



Mean dew-point 3'32 



Correction '22 



3-24 



3-10 



Difference : '14, 



so that a nearer approximation would be obtained. It appears that the last three 

 observations correspond to no physical change in the air, but simply refer to some 

 alteration in what was taken as indicating visible dew. This example well illustrates 

 the uncertainty that rests with dew-point determinations. 



