numerical Relations of the Solar System. 4 1 



to 15° latitude from its equator, and its frigid zone from the 

 pole to 15° latitude, so that Venus's arctic circles are nearer 

 the equator than its tropic, and it must, therefore, have very 

 hot summers and very cold winters, mitigated, however, by 

 the sun's rapid change of declination, and by its year being 

 only two-thirds of ours. Mercury's torrid zone extends only 

 to V^ latitude, its frigid zone commences at 83° latitude, so 

 that 76° of latitude are in the temperate zone, which must 

 diminish the burning heat at that planet very considerably*. 

 The tropics of the other planets being at less than 30° lati- 

 tude, cause no great difference between them and the earth 

 in this respect. 



9. The sun is the principal cause of the difference of mean 

 annual temperature between our pole and equator; therefore 

 as this action diminishes with the planet's distance from the 

 sun, the further the planet, the more equable is its surface- 

 temperature, the less is the elasticity of its atmosphere dis- 

 turbed, and consequently the calmer is the atmosphere, so 

 that the diminished heat and light is compensated by the 

 greater purity and stillness of the atmosphere, allowing those 

 agencies to be more effective. 



London, Aug, 10, 1840. S. M. Drach. 



P.S. The sun's relative limit less unity = 35-3942, which 

 divided by 7 (the number of planets capable of causing serious 

 injury) gives 5-0563. Dividing this last number by 1, 4, 

 and 7, we nearly get the limits (less 1) of the Earth, Jupiter, 

 and Saturn. Applying this principle to Uranus, we have 



y and O , 6: 1 :: 5-056 : 0-843 

 ©, 6:1:: 5-619 : 0-936 

 1/ , 6:4: : 1-319 : 0-879 

 T2 , 6 : 7 : : 0-765 : 0-892 



whereof the mean — 0-887. Hence 1-887 is nearly the 

 relative limit of ^ = 3-984 ;;| p = 0-32597 sidereal day 

 = 8 hours nearly, so that I^ rotates on his axis in 7| to 8 



hours. Also a — -_\ his ellipticity is therefore between — 

 6*7 3 



and — But the Earth's and Jupiter's actual oblateness is 



13- ' 



nearly a mean between the limits; therefore from analogy the 

 oblateness of lil = } nearly. 

 Sept. 4, 1840. ^' M- ^' 



* This diminution would be materially assisted by an ocean, whose 

 great evaporation would reduce and nearly equalize the temperature. 



