36 COSMOS. 



corresponds with the terrestrial pole than does the thermal 

 eqitator, which connects together the hottest points of all 

 meridians with the geographical equator. Arago concludes, 

 from the gradual decrease of mean temperatures, thit the 

 degree of cold at the northern terrestrial pole is — 13^, if the 

 maximum cold observed by Captain Back at Fort Rehance 

 (62° 46' lat.) in Januar}^ 1834, w^ere actually —70° (—56^-6 

 Cent., or — 45°-3 K-eaum.).^ The lowest temperature that, 

 as far as we know, has as yet been observed on the earth, is 

 probably that noted by Neveroff, at Jakutsk (62° 2' lat.), 

 on the 21st of January, 1838. The instruments used in 

 this observation were compared with his own by Middendorff, 

 whose operations w^ere always conducted with extreme ex- 

 actitude. Neveroff found the temperature on the day above 

 named to be — 76° (or — 48° Reaum.). 



Among the many grounds of uncertainty in obtaining a 

 numerical result for the thermal condition of the regions of 

 space, must be reckoned that of our inability at present to 

 ascertain the mean of the temperatures of the poles of great- 

 est cold of the two hemispheres, owing to our insufficient ac ■ 

 quaintance wdth the meteorology of the antarctic pole, from 

 which the mean annual temperature must be determined. I 

 attach but little physical probability to the hypothesis of Pois- 

 son, that the different regions of space must have a very va- 

 rious temperature, owing to the unequal distribution of heat- 

 radiatmg stars, and that the earth, daring its motion with the 



* Arago, Snr la Tempiralure du Pole et des espaces Cilestes, in the 

 Annuaire du Bureau des Long, jwnr 1825, p. 189, et pour 1834, p. 192; 

 also Saigey, Physique du Globe, 1832, p. 60-76. Svvauberg found, from 

 considerations on refraction, that the temperature of the regions of space 

 was — .58^.5. — Berzelius, Jahresbericht fur 1830, s. 54. Arago, from 

 polar observations, fixed it at — 70^ ; and Pectet at — 76°. Saigey, by 

 calculating the decrease of heat in the atmosphere, from 367 observa- 

 tions made by myself in the chain of the Andes and in Mexico, found it 

 — 85°; and from thermometrical measurements made at Mont Blanc, 

 and dui-ing the aeronautic ascent of Gay-Lussac, — 107°-2. Sir John 

 Horschel (Edinburgh Review, vol. 87, 1848, p. 223) gives it at —132°. 

 We feel considerable surprisf , and have our faith in the correctness of 

 the methods hitherto adopted somewhat shaken, when we find that 

 Poisson, notwithstanding that the mean temperature of Melville Island 

 (74° 47' N. lat.) is — 1° 66', gives the mean temperature of the regions 

 of space at only 8°'6, having obtained his data from purely theoretical 

 premises, according to which the regions of space are wai'mer than tha 

 outer limits of the atmosphere (see the work already referred to, $ 227, 

 p. .520) ; while Pouillet Stales it, from actinometric experiments, to ba 

 •IS low as — 223^0. See Comptes Rcndus de V Academic des Sciences. 

 u,m vii., 1838 p. 25-65. 



