THE SEASON OF THE YEAR. 239 



an epoch at all (save for advanced astronomy) is almost or entirely 

 due to that tilt of the earth's axis which causes the seasons — dry or 

 wet, cold or hot. Without the seasons, in one form or other, we 

 might have been ages longer in discovering the fact that the earth 

 moved round the sun, and that some three hundred and sixty-five 

 days (I omit those important fractions) were needed for its revolu- 

 tion. Certainly, without the seasons, at least to the extent that they 

 occur in the tropics, plant and animal life could hardly have assumed 

 its fixed annual cycles, nor could early men have caught at the idea 

 of the year at all as a period of time, a unit of measurement. 



Before the Glacial epoch, in particular, the discovery of the year, 

 organically or consciously, must have been much more difficult than 

 it is now in high latitudes. It must have been almost as difficult in 

 what are now the temperate zones as it is to-day in the tropics. Far 

 north or south, of course, the length of the day would tell; and 

 within the Arctic and Antarctic Circles the long night would form 

 an unmistakable feature. But if the plane of the equator had always 

 found itself vertical to the sun, there could have been no recognition 

 of the year at all, either organic or conscious. In other words, from 

 the point of view of organic life, the year does not mean the revolu- 

 tion of the earth round the sun: it means the apparent northward 

 and southward movement of the sun on either side of the equator; 

 it means the seasons, whether recognized as winter and summer, or 

 as dry and wet periods. That is really the year as man knows it, as 

 plants and animals have always known it. 



With the coming on of the great cold spell, however, the im- 

 portance of the seasons in the temperate and frigid zones, perhaps 

 also even in the tropics, became much more marked. I will not go 

 here into the suggested reasons for that vast revolution, perhaps the 

 greatest our planet has ever suffered. Most physicists now accept 

 more or less the theory put forward with great ingenuity by Mr. 

 Croll, which sets it down to a period of extreme eccentricity in the 

 earth's orbit; but some weight must also be allowed, as Mr. Alfred 

 Russel Wallace has clearly shown, to the local arrangement of land 

 and water on the globe at the time of its origin, as well as to the 

 occurrence of mountain ranges just then at the poles, and to other 

 purely terrestrial causes. Never before, in all probability, had the 

 poles been occupied by great glacier-clad mountains. It seems most 

 likely, indeed, that we are now practically at the end of the Glacial 

 epoch, and that if only we could once get rid of the polar ice caps, 

 which keep a stock of chilliness always laid on (I speak the quite 

 comprehensible language of everyday life), we might recur forth- 

 with to the warm and almost imperceptible winters of the preglacial 

 period. But, as things stand, the stock of ice at the poles never gets 



