10 L. A. Ihi iter — Gravity Determinations at Sea. 



and hence either omits entirely in his tinal tahles or brackets 

 as doubtful. In the first place the coefficients, b, c and d, can 

 of course only l>e found from observation on a moving vessel. 

 How poorly the A^r's from the harbor observations agree, in 

 general, with those resulting from shore pendulum observations 

 when the former are computed with the values of the unknowns 

 obtained from the observations on the moving vessel, is shown 

 by a table which Hecker gives on p. 159 of his 1910 publica- 

 tion. The differences amount at times to 1/6000 part of g. 

 Hecker believes that the trouble arises chiefly from the fact 

 that observations on a vessel moving and on one at rest are 

 not comparable and, hence, require separate treatment, the 

 difference arising chiefly from the dynamic conditions which 

 enter in on the moving vessel. While he is undoubtedly in 

 the main correct, still he does not appear to see that the un- 

 knowns as he derives them are not strictly instrumental or ship 

 constants, but depend, as has been shown above, upon the area 

 (extent and geographic position) from which they are derived. 

 In any case, beyond revealing the discrepancies, he does not 

 make known any attempt at a satisfactory reduction of the 

 harbor observations. This is doubly unfortunate, first, because 

 the harbor observations ought to furnish the best criteria pos- 

 sible of the absolute accuracy and possibilities of his method 

 of observation, and secondly, since the connection of ocean 

 results with land stations is correspondingly diminished in 

 strength. 



Every series of observations made by Hecker on shore or in 

 port has been investigated, and not a single case of satisfactory 

 reduction or adjustment was found. On his first cruise in 

 1901, in the Atlantic Ocean, from Hamburg to Rio de Janeiro 

 and return to Lisbon, he made shore boiling-point observations 

 at Rio de Janeiro and Lisbon at precisely the same places where 

 be swung his pendulums. There was thus afforded a fine 

 opportunity to test his boiling-point method and the behavior 

 of his instrumental appliances. But he makes no attempt at 

 such a comparison. Instead, he merely adjusts the series of 

 shore observations at Rio de Janeiro, Aug. 21-Sept. 11, 1901, 

 by itself and similarly the series at Lisbon, Oct. 12-17, 1901, 

 again by itself. His observation equation is the same as (5) 

 above with the omission of the terms involving b, c, d, and & 2 , 

 which apply only to observations at sea. While his adjustment 

 improves the individual day's results at each of the two stations, 

 it leaves unaltered the actual mean gravity anomaly observed 

 at each station — in brief, he does not adjust Rio de Janeiro 

 and Lisbon together, and the labor of his painstaking adjust- 

 ments is practically for naught. Hence, if we take the 

 quantities, as derived from Hecker's adjustments (or from the 



