118 



BARUS— THE TRANSPIRATION OF AIR 



[April 21, 



lowering the swimmer, I'd, in the cohimn A. In this way constancy 

 of temperature is secured throughout the cohmm. 



3. Barometer. — The apparatus is obviously useful for ordinary 

 barometric purposes, and provided the temperature, t, of the air 



— M 



^^T 



A 



N— r 



Fig. I. Swimmer and appurtenances. 



at V, is known to .025° C, the barometric height should be deter- 

 minable as far as .1 mm. Apart from this the sensitiveness of the 

 apparatus is surprising. Care must be taken to avoid adiabatic 

 changes of temperature, so that slow manipulation is essential. 

 These and other precautions were pointed out in the original paper 

 (/. c.) 



4. Equations. Manipulation. — Let // be the difference of level 

 of the imprisoned water and the free surface in the reservoir R. 

 Then it follows easilv that 



/ _L // P'- - J^^'J '^ 



P. ~ S^I {i+mlM)-pJp' 



(0 



where // is the corrected height of the barometer (from which the 

 mercury head ecjuivalcnt to the vaptn" pressure of water is to be 



