in that year, the twentieth century beginning with January 1, 1901, that is (to be exact) at the previous midnight, when the day commences by civil reckoning." With these remarks of Mr. Lynn I fully concur, and, so far as I know, all astronomers agree with him. As the discussion will probably again arise at the end of the twentieth century, I would like to put on record here what the scientific opinion was at the close of the nineteenth century. Prof. E. Rutherford, the well-known authority on radium, suggests that possibly radium is a source of heat from within the earth. Traces of radium have been detected in many rocks and soils, and even in sea water. Calculation shows that the total amount distributed through the earth's crust is enormously large, although relatively small "compared with the annual output of coal for the world." The amount of radium necessary to compensate for the present loss of heat from the earth "corresponds to only five parts in one hundred million millions per unit mass," and the "observations of Elster and Gertel show that the radio-activity observed in soils corresponds to the presence of about this proportion of radium."[62] The earth has 12 different motions. These are as follows:-- 1. Rotation on its axis, having a period of 24 hours. 2. Revolution round the sun; period 365¼ days. 3. Precession; period of about 25,765 years. 4. Semi-lunar gravitation; period 28 days. 5. Nutation; period 18½ years. 6. Variation in obliquity of the ecliptic; about 47" in 100 years. 7. Variation of eccentricity of orbit. 8. Change of line of apsides; period about 21,000 years. 9. Planetary perturbations. 10. Change of centre of gravity of whole solar system. 11. General motion of solar system in space. 12. Variation of latitude with several degrees of periodicity.[63] "An amusing story has been told which affords a good illustration of the ignorance and popular notions regarding the tides prevailing even among persons of average intelligence. 'Tell me,' said a man to an eminent living English astronomer not long ago, 'is it still considered probable that the tides are caused by the moon?' The man of science replied that to the best of his belief it was, and then asked in turn whether the inquirer had any serious reason for questioning the relationship. 'Well, I don't know,' was the answer; 'sometimes when there is no moon there seems to be a tide all the same.'"![64] With reference to the force of gravitation, on the earth and other bodies in the universe, Mr. William B. Taylor has well said, "With each revolving year new demonstrations of its absolute precision and of its universal domination serves only to fill the mind with added wonder and with added confidence in the stability and the supremacy of the power in which has been found no variableness neither shadow of turning, but which--the same yesterday, to-day and for ever--