7 6 THE POPULAR SCIENCE MONTHLY. 



Boyd Dawkins has pointed out closely resembling the modern Esqui- 

 mau in form, in his weapons and implements, probably in his cloth- 

 ing, as well as in so many of the animals with which he was associated. 



At this stage man appears to have been ignorant of pottery, to 

 have had no knowledge of agriculture, no domestic animals, except, 

 perhaps, the dog. His weapons were the axe, the spear, and the javelin ; 

 I do not believe he knew the use of the bow, though he was probably 

 acquainted with the lance. He was, of course, ignorant of metal, and 

 his stone implements, though skillfully formed, were of quite different 

 shapes from those of the second stone age, and were never ground. 

 This earlier stone period, when man coexisted with these extinct mam- 

 malia, is known as the Palaeolithic or Early Stone Age, in opposition 

 to the Neolithic or Newer Stone Age. The remains of the mammalia 

 which coexisted with man in prehistoric times have been most care- 

 fully studied by Owen, Lartet, Rtitimeyer, Falconer, Busk, Boyd Daw- 

 kins, and others. The presence of the mammoth, the reindeer, and 

 especially of the musk-ox, indicates a severe, not to say an arctic cli- 

 mate, the existence of which, moreover, was proved by other consid- 

 erations ; while, on the contrary, the hippopotamus requires consider- 

 able warmth. How, then, is this association to be explained ? 



While the climate of the globe is, no doubt, much affected by 

 geographical conditions, the cold of the glacial period was, I believe, 

 mainly due to the eccentricity of the earth's orbit, combined with the 

 obliquity of the ecliptic. The result of the latter condition is a period 

 of twenty-one thousand years, during one half of which the northern 

 hemisphere is warmer than the southern, while during the other ten 

 thousand five hundred years the reverse is the case. At present we 

 are in the former phase, and there is, we know, a vast accumulation of 

 ice at the south pole. But when the earth's orbit is nearly circular, 

 as it is at present, the difference between the two hemispheres is not 

 very great ; on the contrary, as the eccentricity of the orbit increases, 

 the contrast between them increases also. This eccentricity is con- 

 tinually oscillating within certain limits, which Croll and subsequently 

 Stone have calculated out for the last million years. At present, the 

 eccentricity is -016, and the mean temperature of the coldest month in 

 London is about 40. Such has been the state of things for nearly 

 one hundred thousand years ; but before that there was a period, be- 

 ginning three hundred thousand years ago, when the eccentricity of 

 the orbit varied from -26 to "57. The result of this would be greatly 

 to increase the effect due to the obliquity of the orbit ; at certain 

 periods the climate would be much warmer than at present, while at 

 others the number of days in winter would be twenty more, and of 

 summer twenty less than now, while the mean temperature of the 

 coldest month would be lowered 20. We thus get something like a 

 date for the last glacial epoch, and we see that it was not simply a 

 period of cold, but rather one of extremes, each beat of the pendulum 



