L. A. Bmier — Gravity Determinations at Sea. 5 



5 mm ; several settings were made, and both the low and high 

 readings were recorded. To reduce the pumping, Hecker had 

 introduced a special capillary tube in about the middle part of 

 his barometer, and, since his observations were made on large 

 steamers, the pumping of his barometer was generally less than 

 0*5 mm . A careful scrutiny of our observations has encouraged 

 me in the belief that it may be worth while to attempt also 

 gravity work on the " Carnegie," which in her various cruises 

 will have opportunity of getting data in regions not yet cov- 

 ered, and will also at times cut across Hecker's trips. Atten- 

 tion is accordingly being given to the question of refining the 

 instrumental appliances and simplifying the method of reduc- 

 tions. As the best preparation it was thought well to review 

 carefully Hecker's work in order that full advantage might 

 be taken of his experiences in this pioneer work, as also to 

 determine what were the various sources of error and their rela- 

 tive importance. (Cf. Bestimmuny cler Seliwerhraft auf 

 dem Schwarzen Jfeere, etc., Berlin, 1910.) 



Hecker's Ocean Gravity Observations. 



Let us begin with the formulae used, and the theoretical 

 treatment applied to the observations. 



Let A = atmospheric pressure deduced from the temperature of 

 the boiling point of pure water with the aid of tables, 

 as for example Wiebe's, given in the " Landolt-Born- 

 stein Tabellen " for 1905 ; 

 i?=the simultaneously observed atmospheric pressure with 

 a mercurial barometer, reduced to standard temper- 

 ature, to sea-level and to normal gravity for latitude, 

 0=15° ; 



then is B = A — B in mms. mercury. (1) 



Were there no errors of whatever kind attaching to A or B, 

 then B would be the gravity anomaly sought. To convert 

 into cms. of the acceleration of gravity, y, we must multiply 

 equation (1) by the approximate factor, 980/760 = 1*29, 

 hence 



Ay = l - 29 (A — B) in cms. per second. (2) 



The reduction of B to normal gravity is made with the aid 

 of Helmert's formula of 1901* : 



c = ( - 0-002611 cos 20 + 0-000007 cos 2 20) B. (3) 



The coefficient of the second term was adopted by Helmert 

 from the theoretical investigations of "Wiechert and Darwin ; 

 * See note next page. 



