NATURAL PHILOSOPHY. 159 



stitution of the surface of our globe. The temperature of hot springs 

 would gradually sink down to the mean temperature of the earth's 

 crust, volcanic eruptions would cea.se, earthquakes would no longer 

 be felt, and the temperature of the water of the ocean would be sen- 

 sibly altered in many places, circumstances which would doubtless 

 affect the climate in many parts of the world. Especially, it may 

 be presumed that \Ycstern Europe, with its pleasant favorable 

 climate, would become colder, and thus perltci)>s the seat of the 

 power and culture of our race transferred to the milder parts of 

 .North America. 



Be this as it may, for thousands of years to come we can predict 

 no diminution of the temperature of the surface of our globe as a 

 consequence of the cooling of its interior mass; and, so far as his- 

 toric records teacli, the climates, the temperatures of thermal springs, 

 and the intensity and frequency of volcanic eruptions are now the 

 same as they were in the far past. 



It was different in prehistoric times, when for centuries the earth's 

 surface was heated by internal fire, when mammoths lived in the now 

 uninhabitable polar regions, and when the tree-ferns and the tropical 

 shell-fish, whose fossil remains are now especially preserved in the 

 coal-formation, were at home in all parts of the world. 



THE INTENSITY OF SOLAR RADIATION. 



The intensity of the solar radiation at different seasons of the year 

 has been investigated by Father Secchi of the Observatory at Rome. 

 We give some results from his paper recently printed in the Comptes 

 Rendus of the Academy of Sciences at Paris. We have not space for 

 the description of the apparatus employed, and with which he made a 

 great number of observations during the summer, repeating them 

 during the perfectly clear days between Nov. 22 and Dec. 8, last, 

 when he exposed the apparatus to the solar radiation under the dome 

 of the observatory until the temperature remained perfectly constant 

 for a considerable time. 1. During the summer, near the meridian 

 and near the solstice, the relative temperature varied from 14 to 11 

 Cent. ; the mean being 12*00. 2. The observations continued during 

 August gave 13 to 11: the mean 12. 3. Those made in November 

 and December gave 12'5, 11'5, the mean not being sensibly changed. 

 4. When observing in summer, near the horizon, at an elevation of 

 30 to 34, he found the temperature rose only to G'5. 5. The rapid- 

 ity with which the blackened thermometer rose was scarcely different 

 in summer from winter until 10 or 11 ; but after this limit the maxi- 

 mum was attained sooner in summer than in winter. The results ob- 

 tained in the latter season were completely unexpected. Father 

 Secchi thought tjhat observing the sun at a height of about 28, he 

 would find a temperature quite, or nearly equal to that which he found 

 in summer at 32 of elevation, the atmospheric density being nearly 

 the same; but it was not so. At the meridian he found nearly the 

 same amount as in summer, although the rays traversed a thickness of 

 atmosphere more than double, while this double thickness diminished 

 the force of the radiation, reducing it to the half. These phenomena 

 would be inexplicable if we did not know the absorbing power of 

 the aqueous vapor. Father Secchi expresses his agreement with the 



