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



boiling point; we may possibly find that this term can he taken 

 account of by the special observations for &, as mentioned 

 above. 



j n 



Hecker's term a -, . is to be eliminated partly by method 



of observation and partly by refinement of instrumental 

 appliances. The three terms, bp + cr + ds of his equation 

 (No. 5), supposed to represent the effects of the ship's motions, 

 we shall endeavor to make negligible as far as possible or reduce 

 to one term, bp, partly by the manner and place of mounting 

 and by construction of the barometers, and partly by the scheme 

 of combination of the observations, so as to introduce varied 

 conditions of motions of vessel. It is thus hoped to avoid any 

 need of a laborious and time-consuming adjustment of the 

 ocean results, thereby enabling the observer to make as nearly 

 a complete reduction of his observations aboard as may be 

 possible, the determination of the effects from instrumental 

 causes disclosed by the shore and harbor observations being 

 left to the office computer. 



The various sources of instrumental error — thermometer and 

 barometer — are at present being further examined. It is 

 possible that the temperature of the boiling point will be deter- 

 mined both with mercurial thermometers of special construc- 

 tion and with electrical resistance thermometers. The chief 

 difficulty now appears to be in the sufficient refinement of the 

 barometric work. The hope is entertained, however, that the 

 great importance of getting values of g within the accuracy 

 demanded by geodosisls— about 0'02 or 0'0S cm — will lead some 

 one to discover a method so superior as to eliminate the boiling 

 point-barometer method altogether for ocean gravity work. 



