148 



MR. W. N. SHAW ON HYOROMETRIC METHODS. 



were found to be alike at these different places ; and therefore the factors may be 

 considered as of general application. 



" By means of the numbers in this table the temperatures of the dew-point in the 

 general tables have been calculated ; and these were for many years checked by direct 

 observations with DANIELL'S hygrometer made by me at the Royal Observatory, 

 Greenwich." 



GUTOT'S tables are a very complete set, comprising : 



i. Extended tables based upon REGNAULT'S formulae already given, adapted 



for millimetres and Centigrade degrees, 

 ii. The same adapted for inches and FAHRENHEIT degrees. (These are given 



" for ordinary use.") 

 iii. GLAISHEB'S table of Greenwich factors and an old set of GLAISHER'S 



psychrometrical tables, based upon them and a Greenwich table of 



pressures. (These are given for the purpose of " comparing results.") 



Besides these there are ANGOT'S tables referred to on p. 134, but I am not aware 

 that they are in general use in any country. 



The information may be summarised in the following table : 



NOTE, APEIL 23, 1888 (see p. 83). 



I have assumed REONAULT'S investigation of the behaviour of sulphuric acid tubes (' Annales do 

 Chimie,' vol. 15, 1845) to be conclusive evidence that his acid was efficient for its purpose. His experi- 

 ments wore of two kinds. First, four sulphuric acid tubes were mounted " in series." The first two 

 were at the ordinary temperature, the third at C., and the fourth at 30 C. The first tube gained 

 1'235 gramme in weight when moist air was sent through the four ; the weights of the other three tubes 

 were unaffected. Secondly, air was dried by passing it through three sulphuric acid tubes, each one 

 metre long, the third being in a freezing mixture. The dried air was then led through a weighed vessel 

 containing moist sponge, and thence through two weighed sulphuric acid tubes. The first of these two 



