Latitude and Temperature in Barometric Hypsometry. 153 



The final result is the height of the upper station above the sea- 

 level according to Laplace's complete formula. [For British heights, 

 the corrections in brackets may be omitted.] Fresh observations 

 should be made whenever the temperature does not decrease about 4 

 degrees for a fall of one inch in the barometer. Calculate great 

 heights in sections. 



Ex. 4. The same data as Ex. 1, with the exception of H being 

 the interval kn in the Table of the ' Abridged Gradual Method.' 



B f 20717 

 V 17*931 



B'+b' 38-648 



A 32-1 

 a 25-5 



836-0 



H 9875 

 L 53 



B'-5' 2-786 

 X 52400 



900)893-6 



38-648)145986-400(3777 

 + 6 



•9929 



•0007 for lat. 53 c 



p -9922 



3783 

 X -9922^3 



Approximative differ- 

 ence of level . . . . 



} 



3754 



9875 H 

 -1-8 for 13000 

 —5 for 10000 



3754 



h 13632 feet. 



Since decimals of a foot are rejected, there is always a liability to a 

 difference of 1 or 2 feet between this and the logarithmic method. 

 A difference of 10 feet between this result and that in Ex. 1, is due 

 to the difference in the assumed value of H. 



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 1000j 2000j 3000} 4 000> 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. 



