L. A. Bauer — Gravity Determinations at Sea. 11 



direct observations), we may see what the extent of instru- 

 mental changes may be during even such a brief interval as 

 six weeks, during which, thermometers are subjected to fre- 

 quent and protracted boiling. The mean Ag results for Rio de 

 Janeiro-Lisbon derived from each of four barometers — two 

 eye-reading ones and two photographically recording ones — 

 differ from the pendulum value by -0-105 to -l-0-200 cm , 

 thus exhibiting a range of 0*3. Even the two visual barometers 

 give results from shore observations differing by 0*1 and this 

 in spite of Hecker's laborious method of observation. The 

 mean result here considered for any one barometer depended 

 on 21 boiling point determinations and 8 barometric readings 

 times the number of days, or for Rio de Janeiro, 360 B. Pts 

 and 120 readings of each barometer and for Lisbon 216 B. Pts 

 and 72 readings of each barometer ! 



Hecker made no shore observations by the B. P. method on 

 any of his subsequent cruises, but he made a number in harbors 

 on board vessels at anchor. These also exhibit most marked 

 changes in but a few days, the effects of which if likewise 

 experienced at sea, as must undoubtedly be the case, would 

 exceed in importance the corrective terms 'in equation (5) due 

 to motions of ship. 



In his Black Sea work, Hecker had repeated trouble with his 

 thermometers so as to be obliged to discard some series entirely. 

 The thermometers were made by Fuess of Steglitz of Jena 

 borosilicate glass 59 III. Looking over Hecker's scheme 

 of observations, the suspicion is awakened that he " boiled " too 

 often and too protractedly —a fact he himself began to suspect 

 in his later work. What accuracy was supposed to be 

 gained by excessive observing was lost in resulting instability 

 of his thermometers. The corrections for HecTcer^s thermom- 

 eters were never re-determined after they had once been fur- 

 nished by the German Physikalische Reichsanstalt. Though 

 some of the thermometers had been in use on the three cruises 

 of 1901, 1901 and 1909, practically the same table of thermo- 

 metric corrections is employed throughout. Three of them 

 were provided with zero points but the zeros were never 

 re-determined. The corrections for the various barometers on 

 a standard barometer for various barometric heights were 

 never determined, or if so, they were not used, the observer 

 supposing that all instrumental changes — both of thermometers 

 and of barometers — would fully be taken account of by a con- 

 stant term (k n equation 5) and by a term, e (t—t ), progressing 

 linearly with the elapsed time. Let it be remembered that 

 these two quantities k n and e were not derived from observa- 

 tions at stations where Ag was known from pendulum work, 

 but from the discussion of ocean observations for which a 

 fictitious distribution of gravity anomalies had to be assumed 

 in order that a least-square adjustment could be made. 



