288 Mr. Ellis on Barometric Hypsometry. [May 18, 



2. French metres, Centigrade temperatures. 



Multiply the difference of the barometric readings in any unit by 1 6000, 

 and divide by the sum of the barometric readings. If the result be 300, 

 600, 900, 1200, subtract 0-6, 0-9, 0'9, 0-2; if 1300, 1600, add 0-2, 2-0 

 respectively. 



Subtract 1'3 times the difference of the temperatures of the mercury. 

 Multiply the remainder by the result of first adding 500 to the sum of 

 the temperatures of the air, then dividing by 500, and finally 



adding for latitude 0, 20, 30, 40, 45, 



and subtracting for lat. 90, 70, 60, 50, 45, 



the decimals -0026, -0020, -0013, -0005, 0. 



To this product add the height of the lower station ; and if the sum is 



1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000 

 add -2, -6, 1-4, 2-5, 3'9, 57, 77, 10-1, 

 subtracting the same numbers when the upper numbers are the height of 

 the lower station. 



Fresh observations should be taken whenever the temperature does not 

 decrease about 2 for a fall of 25 millimetres in the barometer. Calculate 

 great heights in sections. 



Ex. 5. Height of St. Cergues, in the Canton de Yaud, on the road 

 from Paris to Geneva, lat. 46. (Ann. Meteor, de Fr., 1849, p. 59.) 



72971 

 67673 



1406-44 



B b 52-98 

 X 16000 



1406-44)847680-00(602-7 

 9 



M'21-5 

 m 1 18-8 



2-7 

 Xl'3 



q 3-5 



A' 21-8 



a' 18-8 



500-0 



500)540-6 



1^408 



1-0812 

 0001 lat. 46 



p 1-0811 



601-8 

 3-5 q 



app. diff. of level 598'3 



598-3 

 X 1-0811^ 



646-8 

 408-0 H x 

 + 2 for 1000 



1055 metres. 



