352 



BAROMETRICAL MEASUREMENT OF HEUiHTS. 



Now let us calculate by the tables, placing side by side the corresponding results 

 given by the formula of Laplace. 



Millim. o o 



Balloon h' = 328.80 T' = — 9.5 V = — 9.5 



Paris h = 765.68 T = + 30.8 t = + 30.8 



Rleires. 



h' = 328.80 \ rr ,, r . ( 1478.4 By the formula of 



. ^ ih' =z 328.80 ) ^ ^, T • i 

 ''''^ [ h = 765.68 i ^"^'" ^' ^''^' \ 



8209.8 Laplace we found : 



A = 6731.4 

 with (T' — T) = — 40° .3, Table IL gives a = —52.0 



Metres. 



(A + g) = 6679.4 6679.79 



with L = 48° 50', Table HI. gives a = — 2.3 — 2.53 



(A -f a 4- ^) = 6677.1 6677.26 



with 2 (t -{- V) direct calculation gives v = -\- 284.5 -f- 284.45 



(A 4- a 4- ^ -f v) = 6961.6 6961.71 



with 6960, Table IV. gives b = -f 25.1 + 25.03 



(A-fa + /3-|-i;4-8) = 6986.7 6986.74 



Altitude of barometer at Paris = + 48.7 4- 48.70 



Therefore altitude of balloon = 7035.4 7035.44 



Two results which are sensibly identical. This ought not to astonish us ; the tables 

 being the exact development of the formula, they ought to give the same results, 

 provided in both cases nothing has been neglected, and the four factors have been 

 calculated in the same relative order. 



Delcros. 



Disposition and Use of the Tables. 



The disposition of the tables is the following : — 



In Table I., the first column on the left contains the height of the barometer m 

 millimetres, corrected for the error of the instrument. 



The second column headed N (number), gives in metres the first two figures of 

 the number corresponding to each height of the barometer in the first column ; the 

 thiixl column, headed 0.0, gives the remaining figures for the full number of milli- 

 metres ; the following columns give the remaining figures for the same number of 

 millimetres and each decimal fraction of a millimetre which may follow it. The 

 value of the hundredths is to be found in the last column. 



Examples — Height of Barometer = 761.00. 



We look out in the first column for the number 761, and we find on the same line 

 in the second column, 81 ; in the third column, headed 0.0, or full number. 61.1. 

 The corresponding number is thus 8161.1 metres. 



D i-^ 



