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 



