Dr. CrolPs Hypotheses on Geological Climates. 231 



question of that kind ; but I have shown that the errors are 

 enormous, amounting to 100° F. and more, i. e. they are 

 greater than the difference of annual temperature between the 

 equator and the north pole. 



There is certainly a mistake somewhere, or, rather, the whole 

 method is a failure. How can we judge of the change of 

 temperature resulting from this or that distance from the sun, 

 even if we knew accurately the temperature of space*, when 

 we do not know the diathermancy of the atmosphere under 

 different conditions ? We know only that it is exceedingly 

 different according to the different quantities of carbonic acid 

 and aqueous vapour contained in it, and in a far higher degree 

 according to the absence or presence, in different quantities, of 

 suspended liquid and solid particles (clouds, dust, smoke, &c). 

 Thus, when we do not know how far the loss of heat is im- 

 peded, even an accurate knowledge of the temperature of 

 space would be of small use in this matter. 



I will illustrate this by a homely example. Take a room 

 where the fire is extinguished and the hearth or stove cold in 

 the evening, and try to guess at the temperature the room 

 will have in the morning. If we followed the method of 

 Dr. Croll, we should inquire only about the outside tempera- 

 ture, and not about the thickness of the walls, the windows, &c. 

 I think that, taking the average construction of Russian, 

 English, and Italian houses, if the inside temperature was in 

 all three cases 65° in the evening, and the outside temperature 

 — 20° in Russia, 32° in England, and 45° in Italy, the morn- 

 ing temperatures in the room would not be very different, and 

 probably even higher in the Russian room owing to its thick 

 walls, double windows, &c. 



It is also interesting to note that a calculation by the method 

 of Dr. Croll of the mean January temperature under 60° N". 

 as given above, gives lower figures than the extreme minimum 

 anywhere observed by reliable thermometers ; this latter is 

 about -90°>4 F. (-68° C). Neither in the coldest part of 

 N.E. Siberia nor in the highest latitudes of Greenland and 

 Grinnell-land have lower temperatures been noted ; and yet in 

 Floeberg Beach the sun is absent from the horizon more than 

 four months. The lower we make the temperature of space, 

 the more conspicuous is the tenacity with which the surface 

 of the earth and the lower stratum of air retain a relatively 

 high temperature. 



Dr. Croll says, in ' Climate and Time,' p. 43, " The stoppage 

 of all currents would raise the temperature of the equator 



* I just see that Prof. Langley has determined the temperature of 

 space ; but the actual figures and all details are still wanting. 



R 2 



