Dkcembek 16, 1898.] 



SCIENCE. 



843 



The knife-edges can be illuminated in any 

 direction by means of movable mirrors, and 

 the field of view is kept at the same time 

 uniformly lighted. Experiments with an 

 ■electric magnet have shown that the earth's 

 magnetic force only exercises a retarding 

 influence on the swinging, without having 

 any efifect on the resulting length of the 

 mathematical seconds pendulum. The pos- 

 sible slight movement of the agate plate, 

 as well as the slip of the knives, is observed 

 by a specially designed apparatus. 



It is worthy of mention in this connec- 

 tion that up to the present time nearly 

 1,400 gravity stations have been occupied, 

 of which 1,228 are different. Austria heads 

 the list with 698, Germany follows with 

 162, and the United States comes next with 

 88. The greater part of the remainder falls 

 to Denmark, Eussia, Switzerland, France 

 and Italy. About fifteen different nationali- 

 ties are represented in this work. The 

 latest results from pendulum observations 

 are with reference to changes of the force 

 of gravity with elevation, and the deriva- 

 tion of a new formula for the length of the 

 seconds pendulum at the sea-level. From 

 a discussion of over 500 stations the con- 

 clusion is reached that what is usually 

 known as continental attraction amounts 

 practically to nothing, and that in general 

 the change of the force of gravity at any 

 point on the earth's surface depends purely 

 and simply on the Newtonian law of the 

 inverse square of the distance. The intro- 

 duction of a spherical function of the third 

 order in the formula for L, alluded to above, 

 foreshadows the determination of a different 

 ■curvature for the northern and southern 

 hemispheres of the earth; yet tne coefficient 

 appears so small that the inequality cannot 

 as yet be safely predicted. The compres- 

 sion given is 1/297 and the equatorial value 

 of the force of gravity is about 1/13,000 

 greater than that now accepted. The in- 

 vestigation of the relation between disturb- 



ances in the force of gravity and deviations 

 of the plumb line is one of the most interest- 

 ing problems of the near future. 



The reports read by the different dele- 

 gates need not be taken up here. Al- 

 though full of interest to the geodesist and 

 astronomer, they are too voluminous to be 

 analyzed or discussed in the short space at 

 our disposal. They will, however, be pub- 

 lished in full, and will appear in the Pro- 

 ceedings of the conference, where they may 

 be consulted and studied. 



Three matters of universal interest were 

 brought before the Association, and suitable 

 action was had thereon. These were : I. 

 ' The determination of the figure of the 

 earth bj' the measurement of arcs and the 

 determination of the force of gravity.' II. 

 ' Theremeasurement of the Peruvian arc' 

 III. ' The redetermination of the difference 

 of longitude between Paris and Greenwich.' 

 The first two subjects were introduced as 

 resolutions by the United States delegate, 

 and brought out interesting discussions. 

 The first was proposed for the sake of direct- 

 ing the attention of the Association more 

 specifically to the prime object of its exist- 

 ence. No one doubts the utility or neces- 

 sity of a complete study of the law govern- 

 ing the changes of latitude, but its ultimate 

 bearing is rather one of astronomy than 

 geodesy. The funds of the Association are 

 now being devoted largely to the latitude 

 question, and the time seemed fitting to sug- 

 gest work more directly in the line of its 

 avowed purpose— the measurement of the 

 earth. The object of the resolution was, 

 therefore, in the nature of a recall to the 

 original conception of its being, and be- 

 spoke in the interest of pure geodesy an ap- 

 plication of its resources to a realization of 

 the idea of its founders. 



The remeasurement of the Peruvian arc 

 now appears to be assured. It may be 

 worth while just here to recall the essential 

 features of this work. One hundred and 



