AEROSTATICS. 247 



pansion of a column of quicksilver, of which the 

 length is 1, for 1 of heat ; h being the perpendi- 

 cular height (in fathoms) of the one station above 

 the other, 



= 10000 (1+.OOS44 - 



n being nearly = _ _ . 

 10000 



When the centesimal thermometer is used, because the 

 beginning of the scale agrees with the temperature^ 

 so thaty 0, the formula becomes more simple ; and 

 if the expansion for air and mercury be both adapt- 

 ed to the degrees of that scale, 



* = 10000(1 + .00441 (!+*-) log f(l+ ^ 



342. LA PLACE has given a formula for baro- 

 metric measurement somewhat different from the 

 preceding. If t and t' be the temperatures accord- 

 ing to the centesimal thermometer, all other things 

 remaining as above, the height in metres, or 



5412 



In 



