102 



MR W. N. SHAW ON HYGROMETRTC METHODS. 



The differences were still larger in the earlier observations, beginning indeed with 

 a whole degree, but with continued practice they diminished, and after a time became 

 no longer perceptible. As a rule, however, the observation of the dew-point fell to 

 my share. It was necessary, in order to prevent unconscious bias towards a known 

 result, that the observer who read the dew-point temperature should not know what 

 the saturator thermometer was indicating, and in the division of duty I took the 

 dew-point readings ; but, as I have said, in the later observations our readings agreed, 

 and if we exchanged the duties there was no recognisable difference. 



1 9. With the utmost anxiety to be quite fair and to observe only what was really 

 to be seen, it was sometimes difficult to form a satisfactory opinion as to whether a 

 deposit was on the thimble or not. Here, for instance, are some notes made on dew- 

 point readings during Experiment 6 (air temperature 15 C.) : 



In this case the observation was exceptionally difficult in consequence of the slower 

 rate of aspiration. According to the assumption, I ought to have seen the deposit 

 when the temperature reading was below 9'24, and not otherwise. At other times 

 observations seemed to be easier ; the following is extracted from my note-book for 

 the next experiment : 



Saturator temperature 12-6-1275. Mean 12'68. Correction 0'42. 



Mean theoretical dew-point 12 '2 6. 



