AND THE OTHER PLANETS OF THE SOLAR SYSTEM. 665 



and the mean temperature of the pole 



4 16°,5 (C). 



The former of these temperatures would doubtless be much reduced by a lateral transference 

 of heat both to the north and south from the equatorial regions, by which we may conceive 

 the mean temperature of those regions to be reduced to between 70° and 80° (C). The mean 

 temperature of the poles would probably be somewhat greater than the above. 



The greatest value of the annual inequality at the poles would be nearly twice as great as 



at present, or about 



±32° (C). 



Such would be the temperature of Venus in her equatorial and polar regions, with inter- 

 mediate temperatures for the intermediate regions, supposing her to have the same atmosphere 

 as the Earth, and her superficial crust to have the same properties with respect to heat as that 



of our own globe. By a diminution of the atmosphere and an increase of the value of — 



(Art. 27), both the mean temperature and the annual inequality might be diminished in any 

 assigned degree. 



34. I have here supposed the obliquity in Venus to be the same as that of the Earth, but 

 the observations on this planet are so difficult to make as to leave the determination of this 

 element in great uncertainty. It has been estimated by some astronomers at as much as 70° 

 or 75°, and more recently M. de Vico has estimated the inclination of the equatorial plane of 

 Venus to the ecliptic at 53°. 11*. 26"*. Allowing this amount of obliquity, the seasons of 

 Venus must manifestly be utterly different from the terrestrial seasons. In this uncertainty as 

 to the real obliquity in this planet, I will take the extreme case of 75°. The temperatures 

 being calculated for this and the case already given, it will not be difficult to form a general 

 estimate for any intermediate case. 



I have calculated the values of Q by PoissoiVs formulae +, with an obliquity of 75°, for the 

 equator, the arctic circle (latitude of 15"), and for the pole, cases for which the general 

 expression for Q becomes much simplified. I thus find the values of Q to be 



,685 at the Equator, 

 ,701 in lat. 15°, 

 ,966 at the Pole. 



The semi-annual inequality of temperature becomes, in this case, of importance in the region 

 corresponding to our tropical region, extended in Venus to 75° of latitude. Its value depends 

 on Qi the value of which I have calculated for the equator, where this inequality has its 

 greatest relative importance. I find 



Q, = ,355. 



* See The Planetary Worlds, by Sir Breen, of the Cambridge Observatory, p. 154. 

 + Theorie de la Chaleur, Art. 215. 



85—2 



