264 S. Neiocomb—CrolTs Climate and Time, 



received from the sun, the problem of climate would be a quite 

 simple one. But the atmosphere, and especially the vapors sus- 

 pended in the atmosphere, exert a powerful influence in various 

 ways. Perhaps the most general and wide-spread source of 

 this influence may be found in the probable unequal diather- 

 macy of the atmosphere to solar and terrestrial heat which may 

 result in the mean temperature being higher than it would be 

 if there were no atmosphere. To investigate this influence the 

 first datum necessary is the mean temperature, first of the whole 

 earth and then of its various zones, which would be maintained 

 if there were no atmosphere. In other words, we wish to know 

 what would be the temperature of a small solid body revolving 

 round the sun at the mean distance of the earth, and presenting 

 all its sides equally to the sun in rapid succession. This tem- 

 perature may be called the normal temperature of the region in 

 which the earth is moving. 



We repeat that the foundation stone of any reliable investi- 

 gation of terrestrial climate, with respect to its causes, must be 

 a knowledge of this normal temperature. Without it we may 

 have any quantity of material for "' • ^ - --^- 



but nothing 

 the slij ' 

 ; many other questic 



hich we can base a theory worthy of the slightest confidence, 

 to follow it, but this 



the 



.„^ ^ _ „ _^ ^, ^_ ^ who 



attempts to make a geodetic measurement first meets with the 

 question of the length of his measuring rod. Now, no stronger 

 example of the chaotic state of the theory of cosmical heat can 

 be given than the simple fact that not only is this normal 

 temperature entirely unknown, but, so far as we are aware, 

 no attempt has ever been made to determine it. What adds 

 to our surprise is that while no one has attempted to deter- 

 mine what temperature a body like the earth would acquire in 

 free space exposed to the solar rays, there have been a number 

 of attempts to answer the experimentally impossible question 

 what temperature such a body would acquire if the solar heat 

 were cut off; so that the body should be exposed to stellar radi- 

 ation alone, a temperature known in our books as that of space. 



In justice to physicists it must be said that one step toward 

 determining this fundamental temperature was taken many 

 years ago. Pouillet and Herschel determined the actual quan- 

 tity of heat radiated by the sun, and their results have been ot 

 the greatest value in investigating the thermal relations of the 

 solar system. The remaining part of the problem is more la- 

 borious, but not, we conceive, more difficult. 



Since Mr. Croll had not at hand the means of commencing a 

 complete investigation of the causes on which terrestrial climate 

 depends, his theorv must, of necessity, fail to be entirely con- 

 clusive. Still it is worked out in a manner so labonous as to 



