10 



SCIENCE 



[N. S. Vol. XLIV. No. 1123 



the Coast and Geodetic Survey to this field 

 of geodesy are given in the results of more 

 than 30 foreign stations and of nearly 200 

 stations in the United States. 



Happily the gravity conference held in 

 1882 endorsed the plan of using the invari- 

 able pendulum, and of employing the dif- 

 ferential method of carrying on gravity 

 work, and the Survey's present excellent 

 equipment and methods are the direct re- 

 sults. In its present type of apparatus, 

 known as the Mendenhall pendulums, the 

 Survey has a form which for compactness, 

 portability, precision and ease of operation 

 ranks well among the highest in this field 

 of endeavor. 



Two features in recent gravity work are 

 worthy of note. One is the application of 

 the interferometer to the measurement of 

 the flexure of the pendulum support, thus 

 giving a direct measurement of this small 

 quantity in terms of a wave-length of light. 

 It is believed that the resulting corrections 

 to the period of the pendulum are more 

 accurate than those by the older static 

 method where the corrections were derived 

 under exaggerated conditions. The inter- 

 ferometer has been in use for about 8 years 

 as a field instrument, and determinations 

 of the flexure have been made at about 140 

 gravity stations, through a very wide range 

 of conditions in piers and external vibra- 

 tions. 



The second feature worthy of note in re- 

 cent gravity work is the deriving of the 

 rate of the chronometers by Western Union 

 time signals at noon — a distinct advantage 

 over the older method. By it the local time 

 observations are dispensed with, the time 

 of occupation of a station is decreased and 

 the labor of preparing the station greatly 

 lessened, all of which contribute to a lower- 

 ing of the cost per station occupied. In 

 connection with this it is interesting to note 

 that Assistant Schott in 1882 made the 

 statement that 



Time furnished telegraphically by an observa- 

 tory whose clock is protected from changes of tem- 

 perature and pressure will be preferable to any 

 local determination at a field station. 



FIELD AND OFFICE FORCE 



Little has been said of the men who have 

 composed and do now compose the field and 

 office force of the Coast and Geodetic Sur- 

 vey. What the Survey is and accomplishes 

 is due to these men, and to the spirit which 

 influences them. To them must be given 

 the credit for much that the Survey has 

 contributed to geodesy. It would be diffi- 

 cult to find a body of men of greater enthu- 

 siasm for, or a higher scientific attitude to- 

 ward their work. They have a careful de- 

 votion, to duty and an interest in the suc- 

 cess of the Survey and its work, a fact 

 which has developed a corps of workers of 

 unrivalled excellence. 



They have ever been most alert to adapt 

 new discoveries, made in the various fields 

 of science, to the needs of the Survey, and 

 to plan new and improved instruments; 

 while to the theoretical work of geodesy 

 they have added much by critical discussion 

 and extensive study of results. 



Workers must have tools, and this fine 

 body of skilled observers would be seriously 

 handicapped in their work if suitable equip- 

 ment were not furnished them. The Survey 

 is particularly fortunate in having a body 

 of skilled artisans in the Instrument Divi- 

 sion, under the supervision of a most highly 

 efficient officer. In this division there have 

 been designed or built nearly all of the in- 

 struments of precision which have helped 

 so materially to place the Coast and Geo- 

 detic Survey in its present high position. 



Of the relation of the geodetic work of 

 the Survey to that of the world, as shown 

 by its share in the operations of the Inter- 

 national Geodetic Conference, only slight 

 reference is here made, for this subject is 

 dealt with in another address by the former 



