582 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1931 



up a beautiful theory of the tidal evolution of the earth-moon sys- 

 tem, including the separation of the moon from the earth by fission, 

 on the hypothesis that the earth as a whole is a viscous body. A 

 number of us in 1909 had concluded from dynamical and geophysical 

 considerations that the theory of tidal evolution is quantitatively 

 errroneous. The tide experiment and the associated laborious 

 mathematical work were undertaken cooperatively for the purpose 

 of testing the basic hypothesis of the tidal theory. As scientists 

 generally know, it was found that the earth on the whole is as stiff 

 and as elastic as steel. 



The brilliancy of Michelson as an experimenter is well illustrated 

 by the tide experiment. Although the radius of the earth is uncer- 

 tain by several hundred feet, he measured the variations it under- 

 goes as a consequence of the tidal forces of the moon and the sun 

 to within one-hundredth of an inch. The final series of measure- 

 ments, extending throughout all of 1917, were automatically recorded 

 on motion picture film by the aid of his interferometer. 



Another adaption of the interferometer led to a means of measur- 

 ing the diameters of minute satellites and planetoids and of the 

 larger of the stars. It is applicable also to measuring the distances 

 between the components of double stars which are so close together 

 as to be completely inseparable by the most powerful telescopes. 



Although Michelson's work has had an enormous influence on 

 science and will be referred to as basic for generations to come, he 

 published a relatively small number of papers and books, only about 

 75 in all. He never rushed into print with immature work. He was 

 not in the habit of publishing the same thing over and over again in 

 slightly varying form. He did not run around the country, posing 

 as a genius and addressing minor scientific organizations. He never 

 invited the press to carefully timed dramatic announcements before 

 the major scientific societies. He never proclaimed the explosion 

 of the universe. He never attracted popular attention and approval 

 by claiming to find support for theological dogmas or the doctrine 

 of the freedom of the will in the laws of falling bodies or in any 

 other scientific principles. Instead, he pursued his modest and 

 serene way along the frontiers of science, entering new pathways 

 and ascending to unattained heights as leisurely and as easily as 

 though he were taking an evening stroll. 



