PACIFIC EXPLORATION: J. F. HAYFORD 
395 
on land. On the seas a given amount of observing will produce most 
progress if that observing is done on the Pacific. 
In geodesy, gravity determinations furnish the most powerful, the 
most accurate, known method of measuring the flattening of the earth, 
and thereby furnish the most severe, and therefore the most valuable, 
single test of the reliability of conclusions drawn from the deflections 
of the vertical which are put in evidence by triangulation and astronomic 
observations. 
So also when conclusions have been reached as to the completeness 
and location of isostatic compensation on the basis of observed deflec- 
tions of the vertical the most valuable single test of those conclusions 
is furnished by observed values of gravity. 
The geodetic evidence as to the completeness and location of isostatic 
compensation furnishes effective tests of the validity of an important 
group of the fundamental ideas of geology. These tests are being 
applied by the geologists more frequently and more energetically each 
year. 
Moreover, it has recently been shown by Mr. William Bowie, ^ that 
after observed values of gravity have been corrected for isostatic com- 
pensation the remaining anomalies, indicating outstanding excesses or 
deficiencies of density beneath the surface of the earth are, in some cases 
at least, related to the geological history of the region. It is probable 
that in due time geodesy will, in this line, furnish additional help to 
geology. 
In general geodesy furnishes the most powerful know^n means of 
investigating the distribution of density beneath the earth's surface, 
to a moderate depth, say 200 miles. Hence any geological premise 
which depends on assumptions as to the distribution of densities, within 
that 200 mile zone — and there are many such premises — finds a severe 
test in the geodetic evidence. So geodesy may, and will, help the prog- 
ress of geology. 
Suppose it is granted that it is important to secure additional gravity 
observations. Why is it especially important to secure the additional 
observations at sea rather than on land? 
Good determinations of gravity have already been made at 3000 
widely scattered stations on the one-quarter of the earth's surface which 
is land. No reliable observations of the necessary degree of accuracy 
have been made on the three-fourths of the earth's surface which is 
covered by water. 
As soon as it becomes possible to determine gravity satisfactorily 
on a moving ship at sea, it will be possible to secure observations so 
