0. Ilecker — Gravity Determinations at Sea. 389 



difference between gravity observed on board, and gravity 

 determined from pendulum observations at land stations, 

 where the vessel passed, reduced to the geographic position of 

 the ship. In my second work, page 109, those places are 

 especially mentioned. Thirdly, during the two cruises on the 

 Pacific, the term \ does not enter at all into the equations, any 

 more than does the term e(t — 1 ) ; here the changes propor- 

 tional to the time are determined by the observations made in 

 the ports. Bauer seems not to have noticed that. As to the 

 three last-named cruises, a term /A is introduced, which takes 

 into account the difference of the period of the upward and 

 downward movements of the vessel. That also seems to have 

 been overlooked by him. 



Moreover, Bauer claims that, according to the adjustment of 

 the observations on one cruise, I must admit that the local 

 anomalies have the character of accidental errors, and conse- 

 quently that the mean anomaly of gravity on a cruise must 

 theoretically be equal to zero. Evidently this is with him the 

 chief basis for estimating the value of my observations. But 

 it is incomprehensible how he can make such a statement, 

 which does not at all agree with the method of my adjustment. 

 As one reason for its inaccuracy, it may be stated that account 

 has been taken of the difference of gravity on the deep sea and 

 on the shallow sea, relatively to land stations, when observations 

 of both kinds enter into the equations. 



But there is still another reason why his statement is errone- 

 ous. Every one who reads Bauer's remark must infer that all 

 the observations enter into the equation. But, as is stated 

 quite clearly on page 194 of my second work, all the observa- 

 tions made on the deep sea have not been taken into account 

 for the adjustment, but only those made at places where the 

 bottom of the sea was of uniform depth, as shown by the 

 hydrographic charts, that is, where there were no marked ele- 

 vations and depressions, in consequence of which no important 

 anomalies of gravity were to be expected. 



Of the 62 observations on the cruise from Bremerhafen to 

 Melbourne, for instance, 16 deep-sea observations only enter 

 into the equations ; of the 44 observations on the cruise from 

 Sydney to San Francisco, 20 only ; and for the cruise from San 

 Francisco to Yokohama, 21 out of 44 have been taken into 

 account for the adjustment. 



The influence of the movement of the ship has been derived 

 from these observations, and the influence thus determined 

 was taken into account for all the other observations. Bauer's 

 assertion, therefore, is entirely wrong. 



He seems surprised that I have not reduced together the 

 observations made on shore in Bio de Janeiro and Lisbon, and 



