AND THE OTHER PLANETS OP THE SOLAR SYSTEM. 661 



lower than the actual mean temperature of the N. pole. The mean temperature of the pole, 

 at the distance of Jupiter, would manifestly very little exceed - 39°,5 (C). 



The annual inequality in the temperature in any latitude (it) would be about 



16°,44 . 

 ± sin u 



27 



=- ± 0°,G sin /u, 



so that the temperature at each place would be sensibly constant during the year; and in 

 passing from the equator to the poles the whole change of temperature would never exceed 

 about 3° (C). 



Such would be the temperature of the Earth revolving about the Sun in Jupiter's orbit, 

 and having her axis of rotation inclined at the same angle as at present to the plane of her 

 orbit. I omit all consideration of the effect which a reduced general temperature of the lower 

 portion of her atmosphere would have upon its height, density, transmissive power, &c., as 

 being unnecessary in the general estimate which only we can here pretend to make, of what 

 would be the thermal condition of the Earth under the circumstances supposed. But if now 

 we suppose her atmosphere to be increased, there would be a corresponding increase of 

 temperature which would be sensibly the same at every point of her surface. It has been 

 shewn that the temperature decreases, according to Mr Welsh's observations, at the rate of 

 3°,37 (F), or 1°,85 (C), for each 1000 feet of ascent ; and since this rate may be regarded as 

 independent of the density (as far as observation has extended), we conclude that if the 

 thickness of the atmosphere were increased by 1000 feet, the mean temperature of the surface 

 of the Earth would, in her actual orbit, be increased by the above amount. If she moved 

 in Jupiter's orbit, there is reason to believe that the increase of temperature under the same 

 circumstances would be somewhat less, on account of the lower temperature to which the 

 surface of the Earth would be reduced in this case, while at the upper limit of the 

 atmosphere it would be the same as at present under our assumed condition of the equality 

 of temperature in surrounding space. I have already pointed out the probable influence of this 

 cause in the result of Mr Welsh's observations (Art. 15), and have given a rough estimate of 

 the effect which it might produce at the pole where the mean temperature is about 80° (F) 

 lower than in our own latitude. Our estimated temperature of the Earth's equator, if she moved 

 in Jupiter's orbit, is still lower by about 37° (F). In this case, therefore, we may conclude 

 that the decrement of temperature in ascending would be somewhat less than it is actually 

 now at the N. or S. pole. Thus, suppose the present decrement at the pole to be 1° (F) 

 for about 400 feet of ascent, instead of about 300 feet as in this latitude ; then the height 

 corresponding to the same decrement of temperature if the Earth moved in Jupiter's orbit 

 might be estimated at about 450 feet. Other causes with which we are but imperfectly 

 acquainted might possibly have some effect also in diminishing the rate of decrement of 

 temperature in ascending; but taking the most unfavourable case that can be supposed, 

 admitting always that stellar heat has the same power as solar heat in radiating through the 

 Earth's atmosphere, the general conclusion that if the Earth moved in Jupiter's orbit, the 

 decrement of temperature in ascending would be something like what I have here stated, is 



