36 



and when the earth is in aphelion during our northern winter. When the earth's 

 orbit is at a period of great eccentricity, which astronomers tell us it was from 

 about 80,000 years ago to 300,000 years ago, and when our northern winter occurs 

 when the earth is in aphelion, or furthest from the sun during that period of great 

 eccentricity of orbit, it is manifest we have a cause in the greater distance of the 

 earth from the sun to account for a considerable depression of temperature during 

 the winter. At present the reverse of the above state of things prevails, for this 

 is not a period of great eccentricity of the earth's orbit, and our winter occurs 

 during perihelion, and not during aphelion, and, therefore, in our northern hemis- 

 phere the winters are milder and the summers cooler than in the opposite state of 

 things. The difference of temperature between that of our present winters and 

 that of the winters in the foregoing supiJositious case can be calculated approxi- 

 mately, as the distance of the earth from the sun in winter is now about 90 

 millions of miles, and in the case of greatest eccentricity of orlsit would be 97 

 millions of miles, or,'^in other words, our earth is 7 millions of miles nearer the 

 sun during our present winters than it was 210,000 years ago. Now, it has been 

 estimated that absolute zero, or the temperature of this earth without any sun at 

 all, would be 490° below the zero upon Fahr. thermometers, and as our winter 

 temperature is called, .39'', it follows that our temperature above the real zero is 

 529°, and as the heat of the sun varies inversely as the square of the sun's distance 

 from our earth, it follows that when the earth was seven millions of miles further 

 off than at present, the temperature of the winter would be 456° or 73° lower than 

 at present ; or, in other words, 34° below our present so-called zero, a temperature 

 quite sufficient to account for a glacial period. Also, during that long time of 

 great eccentricity of orbit of 220,000 years, it must be remembered that about ten 

 periods would occur when the earth was in aphelion during the northern winter, as 

 the aphelion revolves relatively to the equinoxes in 21,000 years. The other 

 cause for a local glacial period is to be found in the elevation of a certain area of 

 country. This elevation may be due to some internal volcanic causes, and of 

 course the result of such elevation would be a diminution of temperature. This 

 cause of glacial action is probably a very common one, and may occur all over the 

 world, as it is now actually happening in Switzerland and in the Himalayas. It is 

 almost impossible to assign any exact date to the length of time such glacial period 

 may have lasted ; but from observation as to the rocks displaced in some cases, an 

 idea of when the disturbance began may be formed. This consideration of how tem- 

 perature and climate may be, over some distinct area, affected by elevation, should 

 always be well weighed by geologists as a possible solution of the cause of Arctic 

 forms of life being found in tropical and sub-tropical regions, and too hasty conclu- 

 sions as to the entire change of climate over the whole world should thus be avoided. 

 While upon the subject of the earth's temperature, I will briefly notice a class of 

 observations, which, in some measure, if we can depend upon the universality of 

 the observations, seem to offer some answer as to the length of time as to which 

 life has been capable of existing upon this planet. I refer to the observations 

 upon the earth's temperature below the surface. It has always been found where- 

 ever experiments of the kind have been made, that the temperature of the earth's 



