Geological Society. 73 



The constant 52384 has heen changed to 52400 to facilitate calcula- 

 tion and to divide the correction for the first two thousand feet, and 

 c' has consequently been altered to c, the tabular values of which 

 were calculated as follows. 



Put *= 52400 ?^ ; = 52400 . J—, 



B+6, 2—y 



whence 



V ~~ 52400 + a? ^) 



Then (e) becomes 



# + c=60309-19.(logB-log6) = -60309'19log(l-?/) . (g) 

 Make x successively =1000, 2000, &c. up to 30,000, and find the 

 corresponding \alues of y from (f) and c from {g). 



As the differences in the values of c are not uniform, slight errors 

 may arise from neglecting second differences in interpolation, but 

 they can scarcely ever affect the result by a single unit, and may 

 therefore be safely disregarded. Laplace's formula itself cannot be 

 depended on within much larger limits. 



The Table of corrections and transformation of Laplace's formula 

 here given allow of the following simplification in the logarithmic 

 calculation of h— H. 



Let logw=log [logB-log 5 — 0-00004. (M—m)] 

 + l-8261420 + log(836 + A + a) 

 =log [log B-log 6-0-00007 . (M'-m')] 



+ 2-0814145 + log(500 + A' + a') 

 =log [log B-log 6-0-00009. (M"-*»")] 

 + 2- 1 783245 + log (400 + A" + a"), 

 then A-H=w+-001 .nl+k"-H.", 



where l-8261420 + log 900=2-0814145-1- log 500 



= 2-1783245 + log400=4-7803845=log 60309-19. 

 This form requires less previous preparation, avoids the logarithms 



of numbers near to unity as (1 + — ), and allows of the use 



J \ 900 / 



of foreign data to obtain the result in English feet, so that it only 



becomes necessary to reduce the height of the lower station to 



English measures. 



GEOLOGICAL SOCIETY. 

 [Continued from vol. xxvi. p. 553.] 

 December 2, 1863. — Professor A. C. Ramsay, President, 

 in the Chair. 

 The following communications were read : — 

 1. " On the Correlation of the Oligocene Deposits of Belgium, 

 Northern Germany, and the South of England." By Herr Adolf 

 von Koenen. Communicated by F. E. Edwards, Esq., F.G.S. 

 Railway-cuttings in the New Forest (Brockenhurst, &c.) have 



