528 Transactions. — Miscellaneous. 



gravity, and set up a secondary rotation on some other axis. 

 We may suppose, for instance, that previous to the Glacial age 

 the axis of second rotation was in some such position as C 1 

 (Plate XLV., fig. 5), under which conditions the pole of daily 

 rotation would have been close to B, the pole of the ecliptic, 

 for many thousands of years, and consequently a uniform 

 climate, without changes from summer to winter, would have 

 prevailed all over the globe, although of course it would have 

 been hotter near the equator than near the poles. If, when 

 the pole reached A at the culmination of the Glacial period, 

 the distribution of land and water were altered to approxi- 

 mately what it is now, so that the pole of the axis of the 

 second rotation were shifted to C, the movement of the pole of 

 daily rotation would gradually diverge from the path of the 

 smaller circle to that of the larger, which it now pursues. 

 This suggestion of General Drayson's is merely a hypothesis, 

 which possibly might account for the more genial climate in 

 arctic regions which geological evidence shows to have 

 existed previous to the Glacial age. The hypothesis would 

 involve a shortening of the period of extreme cold by three 

 or four thousand years. But when once we recognize the 

 fact that any alteration in the form of the surface of the globe 

 which moves the centre of gravity from its symmetrical posi- 

 tion must cause a second rotation about an axis depending 

 upon the balance of the globe at the time, we have a wide 

 field of investigation opened to us as to the possible changes of 

 climate which may have occurred during the past history of 

 the globe. 



In order to show that this cause of a second rotation of 

 our globe is reasonable, we may make a rough comparison 

 between the present conditions of the earth and those experi- 

 mentally produced with a gyroscope. 



The most recent estimates of the extent of land in the 

 Northern and Southern Hemispheres at present give an excess 

 in the former of about 23,000,000 square miles, the greater 

 part of it lying in the eastern part of the hemisphere. 

 Assuming T ^th of a mile, or about 500ft., as the average height 

 of the land above the water, this would give 2,300,000 cubic 

 miles of land. The volume of the globe is 260,000,000,000 

 cubic miles, and its density as a whole is about twice that of 

 the upper strata : hence we find that about ^ 2 fost^ 1 or > sa y» 

 230 1 000 th part of the mass of the earth projects at one point 

 and throws it out of equipoise. Is this a sufficient cause to 

 produce one second revolution in about 32,000 years, equiva- 

 lent to 32,000 x 365 = 11,680,000 daily revolutions? 



I assume the weight of a wheel of a gyroscope to be lib., 

 and that it is revolving fifty times in a second, and make a 

 comparative rule-of-three statement to find how many of these 



