264 
PRESTON. 
this report it is shown how nearly 7,000 equations are used 
to find the quantity sought. It is extremely gratifying to 
note that, although the original observations were made to 
study only changes of latitude, they embodied sufficient 
material to determine with precision one of the fundamental 
constants of astronomy. 
The final values obtained were: 
Constant of aberration. 20Y458 
Solar parallax.. 8".808 
Sun’s distance (miles). 92,820,000 
IY. The International Geodetic Association. 
It is now proposed to state briefly and in very general terms 
what has been done by the International Geodetic Association 
in the question of the measurement of the earth. The first 
idea of cooperation on a grand scale seems to have come from 
General Baeyer. In 1861 he wrote to the Prussian Minister 
of War recommending that the nations of middle Europe 
should combine forces and devote themselves to the solution 
of the problem. Pie called attention to the fact that France 
had undertaken the work on a large scale in the 18th cen¬ 
tury, and England and Russia in the 19th, and that the east¬ 
ern and western parts of the continent were much farther 
advanced in this line of work than his own country. At this 
time only three arcs of the meridian and three arcs of the 
parallel had been measured in Europe, but they had already 
begun to notice the anomalies in the direction of the plumb 
line and were unable to explain the reasons therefor. The 
first and most natural supposition was the attraction of the 
mountains; but when deflections of the plumb line were found 
on extended plains, and, moreover, when, as they then sup¬ 
posed, the great Himalayas exercised no appreciable effect, 
they were led to suppose great changes of density in the 
earth’s surface. Perhaps this phase of the question stim¬ 
ulated as much as anything else the cooperation of the dif¬ 
ferent governments. In any event, during the month of Oc- 
