256 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 
extensive researches in our science. Astronomy is, perhaps more 
than any other, a science which requires long continued and system- 
atic investigations to be carried through with faithfulness, unsel- 
fishness, and untiring perseverance before any definite results can 
be attained. All honor to the astronomers of the past, who spent 
their lives in making observations of which they themselves could 
not hope to reap any fruit, and all honor to the astronomers of the 
present, who are unselfishly collecting data which only a future 
generation can use. The results of past observations are beginning, 
' in many different branches of our science, to be of inestimable 
service in unravelling some of the mysteries of the universe. 
Let us begin our review of the progress of our science at our own 
globe, and though one would hardly state that the science of geo- 
physics, as the study of the form and constitution of the earth is 
called, is astronomy, yet it can not be disputed that only by know- 
ing exactly the dimensions of our earth can we determine the dimen- 
sions and distances of the heavenly bodies; and only from a study 
of the constitution and physical condition of our globe, which must 
include careful measurements of the spectra of terrestrial elements, 
can we determine the constitution, the physical conditions, and the 
radial motions of the heavenly bodies. We have to proceed to 
the inaccessible by a study of the accessible, and to investigate the 
the unknown by attacking the knowable, and hence we may safely 
say that a knowledge of the dimensions and form, the constitution 
and physical condition, of the earth is a first requisite for a satis- 
factory study of the heavenly bodies. The science of geodesy, 
which treats of the figure and size of the earth, is making substantial 
progress all over the world, and new and more accurate data are 
constantly being obtained. It is a great satisfaction to me to 
record that, under the able superintendence of Dr. King, good 
progress is being made in an accurate geodetic survey of Canada. 
This work, which has only recently been organized, will furnish at 
the same time results of the greatest practical usefulness, as well as 
of the highest scientific value. The allied branches of seismology, 
terrestrial magnetism, and of the determination of gravity are, 
along with geodesy, gradually changing and crystallizing our notions 
of the structure of the interior of the earth from the old idea of a 
thin crust surrounding a molten interior to that of a solid globe 
whose density and elasticity increase with the depth, at least for 
some distance, and which acts on the whole as if it possessed the 
rigidity of steel. Geodetic measurements show that all local irregu- 
larities on the surface such as mountains and valleys are completely 
compensated for at a depth of about 75 miles. This means that if, 
from the boundaries of equal areas on any part of the earth’s sur- 
face, lines are drawn toward the center to a depth of 75 miles from 
