TRANSACTIONS OF THE SECTIONS. 49 



Let V = velocity of the air in feet per second. 

 ^=gTa\'ity=:32-18 feet per second. 

 «c=-n'ei<^ht of a cubic foot of air at CO' Falir., and 29-92 inclies tarometric 



pressure =0 070107 lbs. 

 P=pressure in lbs. per square foot of aflat surface held at right angles to the 

 direction of the current of air. 

 Then vnc=r/V. 



Let J) = the height of the column of liquid driven up the tube, measiu-ed in inches. 

 W= weight in lbs. of ^^^ cubic foot of this liquid. 



ffW^ 

 to 



Where the liquid used is water, W=5-20833, and ii = ^ / p . 4G-92, or n=J-—. 



^ ^ 2202 



In the anemometer here described, ether of the specific gravity -740 is employed, 

 and the instrument is so used that the reading is double the actual column of ether 

 supported. In this case 



^■=A/f'^ = V2.. 28-55. 



In order now to see what correction will be necessary when the temperature of 

 the stream of air is different from that of 00" Fahr. 

 Let v= velocity of air at some other temperature, say at the temperature of t de- 

 grees Fahr. 

 w'= weight of a cubic foot of air at that temperature. 

 vol'= volume of a cubic foot of air at that temperature. 



Then ^=}^— ^ 491 / _45n-M 



'"' ''"^ r«/at.32°/l + *'^-"^'\~*'^^^ ' 

 \ 491 / 



1^]_4C9+^. 

 w' w 519 ' 



but ^_ A^orr'= /p^= /.W'W 1 4.59+i! 



V -2 tv 'V 2 w' \/ 2 w 519 ■ 



But it is generally necessary to cany the correction a step fiu'tlier, and to give 

 the velocity in feet of air at 00° temperature. 



Now t.= ,'^_^=t.'^19+< 



vol' 459 



,459+i; „„ „ 459+d 



-V' 





Further, to correct for variations in barometric pressure, 



Let y"= velocity of air at some other pressure than 29-92 inches, say at a 

 pressure of A inches. 

 tr"=weight of a cubic foot of air at that pressure. 

 ro^" = -solume of a cubic foot of air at that pressure. Then 



w_ 29-92 , i^_j:29;92 

 w" J) ' k" w p 

 1869. 4 



