TABLE III. ECCENTRICITY, LONGITUDE OF THE PERIHELION, &c., &c., FOR INTERVALS OF 10,000 YEARS, FROM 1,000,000 TO 700,000 YEARS AGO. THE GLACIAL EPOCH OF THE Miocene period IS PROBABLY COMPREHENDED WITHIN THIS TABLE. TABLE IV. ECCENTRICITY, LONGITUDE OF THE PERIHELION, &C., &c., FOR INTERVALS OF 10,000 YEARS, FROM 250,000 YEARS AGO TO THE I. II. PRESENT DATE. THE Glacial epoch Is PROBABLY COMPREHENDED WITHIN THIS TABLE. III. IV. 898 28.3 10.7 eccentricity at any given period, how much the winter may exceed the summer in length (or the reverse), how much the sun's heat is increased or decreased by a decrease or an increase of distance, and so forth; but we obtain no information whatever regarding how these will actually affect climate. This, as we have already seen, must be determined wholly from physical considerations, and it is an exceedingly complicated problem. An astronomer, unless he has given special attention to the physics of the question, is just as apt to come to a wrong conclusion as any one else. The question involves certain astronomical elements; but when these are determined everything then connected with the matter is purely physical. Nearly all the astronomical elements of the question are comprehended in the accompanying Tables. In Tables II., III., and IV., column I. represents the dates of the periods, column II. the eccentricity, column III. the longitude of the perihelion. In Table IV. the eccentricity and the longitude of the perihelion of the six periods marked with an S are copied from a letter of Mr. Stone to Sir Charles Lyell, published in the Supplement of the Phil. Mag. for June, 1865; the eight periods marked L are copied from M. Leverrier's Table, to which reference has been made. For the correctness of everything else, both in this Table and in the other three, I alone am responsible. Column IV. gives the number of degrees passed over by the perihelion during each 10,000 years. From this column it will be seen how irregular is the motion of the perihelion. At four different periods it had a retrograde motion for 20,000 years. Column V. shows the number of days by which the winter exceeds the summer when the winter occurs in aphelion. Column VI. shows the intensity of the sun's heat during midwinter, when the winter occurs in aphelion, the present midwinter intensity being taken at 1,000. These six columns comprehend all the astronomical part of the Tables. Regarding the correctness of the principles upon which these columns are constructed, there is no diversity of opinion. But these columns |