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



The first point to be made, therefore, on the instrumental 

 side is, that in order to secure desired accuracy in gravity 

 determinations from boiling-point observations, it is essential 

 that a method of observing be adopted which will protect, as 

 nearly as possible, the instruments from changes of whatever 

 kind, and next that the boiling-point thermometers be provided 

 with zero points, the variations of which may be determined in 

 the field with melting ice once a week or as often as may be 

 found necessary. The next point is that the method of 

 observations be such that they can be quickly reduced and that 

 too in such a perfectly definite manner as to admit of no ques- 

 tion with respect to the logical method of reduction to be 

 employed. Hecker, as shown above, did not lay sufficient 

 stress upon these vital points. It is believed that equally 

 good, if not indeed superior results, can be obtained with less 

 equipment than used by Hecker, using a simpler method of 

 observation as well as of reduction. Hecker's cumbersome 

 adjustments at times appear to have caused much needless 

 labor. See, for example, his Black Sea adjustments, where he 

 has attempted to derive his many unknowns from an insuffi- 

 cient range of conditions. 



Another very important point introducing a source of error 

 not considered by Hecker is with regard to the possible errors 

 in the vapor tension tables used to convert boiling-point tem- 

 peratures into corresponding atmospheric pressure. The latest 

 of these tables are those of Wiebe's given in Landolt-JBorn- 

 stein's "Physikalisch-Chemische Tabellen" for 1905. The 

 most recent observations appear to be those of Holborn and 

 Henning. For the purpose of gravity work, it is essential to 

 be able to obtain accurately the atmospheric pressure for a com- 

 paratively limited range extending below and above 100° C: 

 the observations on which the tables are based were made at 

 larger intervals and the interpolation is accordingly somewhat 

 uncertain. It is quite possible that the atmospheric pressure 

 as taken from the tables may be out by -05 to - l mm , which 

 corresponds to 0-065 to 0-135 cm in g. When dealing with only 

 differential results, as we are in our case, the tabular errors are 

 somewhat eliminated, though not wholly. The problem of 

 most accurate vapor-tension tables for water between 99° and 

 101° is here called to the attention of physicists. 



Ilecker's Gravity Results. 

 From the explanatory statements on p. 150 of his 1910 pub- 

 lication, it is seen that Hecker uses a different plane of refer- 

 ence for the gravity anomalies, the A^'s, over each ocean, and 

 that the planes refer strictly only to the parts of the respective 

 oceans traversed. No direct comparison can in consequence 

 be made in passing from one ocean to another and 



