248 L. A. Bauer — Ocean Gravity Observations. 



I have shown (I. <?., p. 10) that his unknown quantities " are 

 not strictly instrumental or ship constants, but depend upon 

 the area (extent and geographic position) from which they are 

 derived." Hecker does not appreciate that they can hence 

 only be used within the area embraced by the stations entering 

 into his adjustments and not outside, for extrapolation pur- 

 poses. For example, in his 1910 revision Hecker assumes that 

 the unknowns derived from selected stations between the 

 Tongas and San Francisco likewise hold for the disturbed 

 region, Sydney to the Tongas. The 1910 computation increases 

 the gravity anomalies between Sydney and Tonga at times by 

 # l cm and more over those of 1908 ; the largest gravity anomaly 

 of all his cruises, +0*393 cm , is now placed in this region, viz., 

 off the north extremity of New Zealand. The 1908 compu- 

 tation, on the other hand, gave as the largest anomaly, -f 0*319 cm , 

 off Honolulu. The Sydney-Tonga region is that for which 

 Hecker appeals to Kohlschutter's paper in confirmation of his 

 work. Kohlschutter's own observations were not made on the 

 ocean but on land, in German East Africa. His general con- 

 clusion would doubtless hold as w T ell for Hecker's 1908 results 

 as for those of 1910. 



Omitting the rejected port observations, it is found for the 

 Atlantic work that 44 out of 47 available results were utilized, 

 whereas for the Indian and Pacific Ocean cruise, out of 136 

 collected results 65 enter into the least square adjustments for 

 the derivation of the required unknowns. Those who must 

 utilize Hecker's anomalies should bear in mind the extent to 

 which they are already subject to the law of accidental distri- 

 bution assumed in the adjustments. It may also be of interest 

 to record here, that for 85 per cent of the total work the appli- 

 cation of correction due to course and speed of vessel and the 

 rejection of the port results has increased the sums of the 

 gravity anomalies squared, the increase being most pronounced 

 where extrapolated coefficients have been used. 



Hecker has overlooked the salient feature of our proposed 

 plan, viz., the prime importance of so arranging observational 

 work as to admit of but one logical method of reduction, and 

 the necessity of restricting the unknowns to a few physically 

 determinable ones. I hope that I shall not be regarded as un- 

 appreciative of his labors. In fact, only one who is himself 

 engaged in ocean observational work can adequately realize 

 the countless difficulties which had to be overcome. My chief 

 aim has been to assist in setting before those who use his 

 results their precise limitations. 



Washington, D. C, January 22, 1912. 



