SEEDS AND THEIR GERMINATION 10"? 



ard death ensues. So with the species. Each generation adds some- 

 thing to the energy of the specific wave until a maximum is reached, 

 re-action sets in, and ultimate extinction follows. In like manner the 

 generic wave includes within its larger grasp a number of specific waves, 

 and is itself included in one of the great ordinal waves, these being 

 but phases of that vast concentrating impulse which originated organic 

 life, and is carrying it forward through ages of progress to a climax 

 yet far distant. 



THE CHANGES OF CLIMATE DURING GEOLOGICAL 

 PERIODS. 



BY THE REV. J. WILSON COOMBS, B.A. 



(Continued from page 80.) 



At present, the distance of the earth from the sun during winter, 

 when nearest to the sun, is nearly 90,000,000 miles. But when the 

 eccentricity is at its superior limit, the distance is 98£ million miles. 

 Now, the northern hemisphere is nearest the sun in winter. This makes the 

 winter both milder and shorter than it would otherwise be. But abo'ut 

 every 10,500 years this state of things is reversed. If, according to the 

 precession of the equinoxes, winter in our northern hemisphere should 

 happen when the earth is in the aphelion of its orbit, at the time when 

 the orbit is at its greatest eccentricity, it would be 8£ million miles 

 further from the sun than it is at present, and the winter would be 

 thirty-six days longer than the summer. Then, as the quantity of heat 

 received from the sun is in inverse proportion to the square of its distance, 

 the heat of the sun would be one-fifth less during the winter season, and 

 one-fifth more during the summer. But, if winter should, at this 

 time of extreme eccentricity, happen when the earth is in the perihelion 

 of its orbit, the earth would then be more than 14,000,000 miles 

 nearer the sun in winter than in summer. In this case, while the one 

 hemisphere would be enduring the greatest extremes of summer heat 

 and winter cold, the other would be enjoying a perpetual summer. The 

 eccentricity is at present diminishing, and will continue to do so during 

 about 24,000 years. It has been small for the last 60,000 years, and no 

 considerable change of climate has occurred during that time. 



There was a period of high eccentricity of 200,000 years, 

 commencing about 2£ million years ago, to which, probably, the 

 glacial epoch of the Eocene age may be referred. A second period 

 in which the eccentricity was very high (still higher than the 

 preceding) may be taken as commencing 850,000 years ago. It 

 extended over a period of nearly 300,000 years, and to it may be referred 

 the glacial epoch of the Miocene age. A third period began about 240,000 

 years ago, and extended over 160,000 years, i.e. to about 80,000 years 

 ago. To this maybe referred the last glacial epoch — the time of the till 

 and boulder clays. At the time of greatest eccentricity during the first 

 (Eocene) epoch, the excess of winter over summer was 33-6 days, the mid- 

 winter intensity of the sun's heat (1,000) = 841. The number of degrees 



