469 



Table III. 



Dry Bulb, 

 Fahr. 



Wet Bulb, 

 Fahr. 



Barometer, 



Fraction of Satura- 

 tion by Weighing. 



Fraction of Satura- 

 tion by Apjohn's 

 Formula. Coef- 

 ficient 88. 



Fraction of Satura- 

 byAugust's mo- 

 dified Formula. 

 Coefficient -429. 



o 



49-37 



o 



48 00 



30-16 



0 -8734 



0 -8712 



0 -904 



47 '42 



46-21 



30-32 



0 -8533 



0-8457 



0 -891 



47-00 



44-17 



29-45 



0 -7436 



0-8013 



0 -797 



45 86 



42-98 



30-39 



0 -8406 



0 -7905 



0 -859 



45-53 



43-19 



29-45 



0-7659 



0-8304 



0-826 



45 -07 



43-72 



30-41 



0-8503 



0-8990 



0-896 



44-34 



40-41 



29-74 



0-6193 



0 -7082 



0-694 



44-78 



44-51 



30-39 



0-9626 



0-9857 



0-979 



42-44 



41 -74 



30-24 



0 8314 



0-9440 



0-943 



42-17 



40-03 



29-87 



0 7576 



0 8311 



0 828 



42-15 



40-17 



29-66 



0-8035 



0-8410 



0-841 



34-47 



34-05 



29-89 



0-9877 



0-9600 



0-959 



33-53 



32-52 



29-74 



0-8183 



0-9020 



0-904 



In these cases also the formulae of Apjohn and August agree pretty 

 nearly ; but both give fractions of saturation very different from those 

 obtained by Regnault's process of weighing the aqueous vapour of the 

 atmosphere. The result of this process, used by Regnault as a test of 

 the efficiency of August's formula, would no doubt be decisive if that 

 result could be obtained by a momentary observation, and at the same 

 moment in which the observations of the wet bulb were made, which is 

 impracticable on account of the length of time required for the trans- 

 mission of a sufficiency of the air operated on through the drying tubes. 

 Regnault himself elsewhere says this method " does not give the quan- 

 tity of humidity which exists in the air at a determinate moment." In 

 an experiment of his, the passage of the air through the drying tube 

 occupied an hour and a half : great changes may occur in that period. 



"We find from the preceding facts and considerations that the formulae 

 proposed by Apjohn and August for ascertaining the dew-point and 

 fraction of saturation by the wet bulb Thermometer do not lead to a 

 coincident result, and that Begnault's weighing process disagrees in 

 general with both formulae, and is not to be viewed as a test of either. 

 So far as absolute precision is concerned, we may say that, of the three 

 methods, not any one is supported by the testimony of either of the 

 other two. It is to be regretted that under these circumstances Eeg- 

 nault did not adduce the evidence of his own " condenser," which tells 

 its story at once without calculation or the introduction of uncertain 

 quantities, although it is subject to errors arising from the difficulty of 

 accurate observation. The only observations quoted by him, made with 

 his condensing Hygrometer, are those of M. Izarin, which are to the 

 full as discordant as any of the rest. 



