. Island life : or, the phenomena and causes of insular faunas and floras, including a revision and attempted solution of the problem of geological climates . y the Gulf-stream warmingthe whole North Atlantic ocean and by the prevalence ofwesterly winds which convey that warmth to our shores;and also by the comparatively small quantity of high landaround the North Pole which does not encourage greataccumulations of ice. But besides this change in the re-lation of our seasons to the earths aphelion and j)erihelionthere is another and still more important astronomical 128 ISLAND LIFE PART 1 fact
. Island life : or, the phenomena and causes of insular faunas and floras, including a revision and attempted solution of the problem of geological climates . y the Gulf-stream warmingthe whole North Atlantic ocean and by the prevalence ofwesterly winds which convey that warmth to our shores;and also by the comparatively small quantity of high landaround the North Pole which does not encourage greataccumulations of ice. But besides this change in the re-lation of our seasons to the earths aphelion and j)erihelionthere is another and still more important astronomical 128 ISLAND LIFE PART 1 factor in the change of magnitude of the excentricity varies very largely, though very slowly, and it is nownearly at a minimum. It also varies very irregularly; butits amount has been calculated for several million yearsback. Fifty thousand years ago it was rather less than itis now, but it then increased, and when we come to a hun-dred thousand years ago there is a difference of eight anda half millions of miles between our distance from the sunin a;phelion and perihelion (as the most distant and nearest PROBABLE DURATION OF THE GLACIAL EPOCH. THOUSAND YEARS AGO FROMA. D. 1800. DIAGRAM OP EXCENTRICITY AND PRECESSION. The dark and light bands mark the phases of precession, the dark showing short mildwinters, and the light long cold winters, the contrast being greater as the excen-tricity is higher. The horizontal dotted line shows the amount of the presentexcentricity. The figures show the maxima and minima of excentricity during thelast 300,000 years from Dr. Crolls Tables. points of the earths orbit are termed). At a hundred andfifty thousand years back it had decreased somewhat—tosix millions of miles; but then it increased again, till attwo hundred thousand years ago it was ten and a quarter,and at two hundred and ten thousand years ten and a halfmillions of miles. By reference to the accompanyingdiagram, which includes the last great period of excentricity,we fi
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