L. A. Bauer — Gravity Determinations at Sea. 3 



in determining between 1896 and 1898 the gravity correction 

 to observed barometric heights at various stations of the Mete- 

 orological Service in Norway. It was Mohn 's success which 

 led Helmert and Hecker to consider this method for ocean 

 gravity observations. 



Hecker, working under the direction of Helmert, has thus 

 far made three expeditions, chiefly at the expense of the Inter- 

 national Geodetic Association, — the first in 1901, in the Atlan- 

 tic from Hamburg to Bio de Janeiro and return to Lisbon ; 

 next in 1904, a cruise extending over the Indian and Pacific 

 Oceans, and finally in 1909 in the Black Sea. All of his work 

 was executed in a most painstaking manner and a very elabo- 

 rate instrumental outfit was used ; the observations were made 

 only on good-sized steamers of 5000 tons and upward. In his 

 Black Sea cruise, of which the results have just appeared, the 

 Russian cruiser "Pruth," of 5500 registered tonnage, was put at 

 his disposal ; his instrumental outfit consisted of six boiling 

 point apparatuses, each provided with a thermometer and two 

 sets of photographically registering barometers, one set having 

 five mercurial barometers and the other four, or nine specially 

 constructed barometers in all. The thermometers were read with 

 a telescope magnifying twenty times, so that to the observer 

 0-001° appeared of the length 0*4 mm . The nine photo-baro- 

 grams were independently read by two assistants and correc- 

 tions for various sources of error were applied. Hecker also 

 devised instruments for photographically recording the ship's 

 motions, with the aid of which further corrections were deter- 

 mined. Finally, an elaborate adjustment by the method of 

 least squares was made of the outstanding -differences between 

 the atmospheric pressure, A, derived from the boiling point 

 work, and that, _Z?, resulting from the barometric readings 

 referred to standard temperature and normal gravity for lati- 

 tude 45°; there were thus determined further corrections, as 

 explained later in this paper. 



The 1901 work was published in 1903, that of 1904 in 1908, 

 and that of 1909 in 1910. In Hecker 's last publication are 

 given, in addition to the Black Sea results, the revised- results 

 of the work done in 1901 and 1904, so that the previous publi- 

 cations are superseded by this latest one. The revisions were 

 made necessary by the correction pointed out by Baron iLotvos 

 due to course and speed of vessel. Hecker 's work in the 

 Black Sea was done partly for the very purpose of testing 

 whether his methods were of sufficient accuracy to detect this 

 theoretical correction ; he reaches an affirmative conclusion and, 

 accordingly, revises his previous reductions. He now also 

 excludes, in the least-square adjustments, observations in ports 



