L. A. Bauer — Gravity Determinations at Sea. 1 



Let c' = correction to an observed mercurial barometric 



height on account of speed and course of moving vessel, 



v = velocity of a point in the equator = 4 - 65 XlO 1 cm./ sec. 



v' = " " ship along a parallel of latitude. 



JZ = earth's mean radius = 6 - 38 X 10 8 cm. 



then is 



_760 %v a v' a , - M ,- - . . ,., 



g'= + — — . — "j- cos" <£=0 - 0146 cos </> in mm. mercury (4) 



980 R j \ j 



— for vessel going east. + for vessel going west. 



To get the correction in cms. g, multiply the tabular quan- 

 tities by 1*29. For a vessel sailing east, for example, along 

 the equator at. the rate of 7 degrees or 420 knots a day, the 

 atmospheric pressure observed on board with a mercurial bar- 

 ometer would have to be diminished by 0"l mm . On the other 

 hand, for the same vessel going west at the same speed, the 

 barometer reading would have to be increased by 0"l mm . In 

 the first case g would be too low by 0'15 cm and in the second 

 too high by the same amount, or the resulting error, if not 

 taken into account between the two occasions, would be 0*30 om 

 or 1/3300 part of g — a respectable quantity. On the average, 

 Hecker's corrections for the vessels on which he made his 

 observations was about ± O'OT 0111 in g; for the " Carnegie " the 

 correction would usually be less than ± 0*03. Since the cor- 

 rection is a perfectly definite one and can readily be computed, 

 it is worth while applying. 



But there are more troublesome sources of disturbance 

 arising from a moving vessel not so readily disposed of as the 

 preceding one — arising from the actual motions of the vessel, 

 such as rolling and yawing, vibration clue to machinery, and 

 worst of all, pitching and accompanying vertical motions. 

 Hecker, as above stated, undertook to determine these sources 

 of error instrumentally with the aid of devices recording the 

 ship's motions. He then determined the reducing coefficients 

 for each effect by a least-square adjustment of all the observa- 

 tions made on any one cruise. The manner of mounting, as 

 compared with those of the barometers, as well as an examina- 

 tion of the results of Hecker's laborious least-square adjust- 

 ments, leads one to question the effectiveness of his devices for 

 the elimination of the ship's effects. 



Next are the errors due to purely instrumental causes, such 

 as changes in the corrections of the thermometers with which 

 the boiling point of pure water is determined, furthermore the 

 relation of the zero of the boiling-point atmospheric pressure 

 to that of the mercury barometer, and the variations in this 

 relation, etc., etc. 



