234 Dr. A. Woeikof s Examination of 



of cooling the air, that at Iquitos the absolute minimum 

 during a year was 66°*8 F. It is clear that in continental 

 regions also, cold winds from the middle latitudes do not 

 reach the equatorial zone. 



It may be fairly asked, Where and how did Dr. Croll get 

 his opinion about the cooling influence of winds from middle 

 latitudes on the temperature of the equatorial regions ? 

 Would it not have been better to inquire about some of the 

 best-known facts of climatology, before speculating " a perte 

 de vue," and bluntly stating that the mean temperature of 

 the equator would be 55° above what it is now, if it was not 

 for the heat-abstracting action of ocean-currents ? Why, on 

 the Upper Amazons there is no such heat-abstraction ; aerial 

 currents can certainly not have a cooling influence of even a 

 degree F.; and yet the mean temperature, reduced to sea-level, 

 is not anything like 135° F., but below 80°. Besides the 

 immense influence of the diathermancy of the atmosphere 

 and its enormous variations in time and place, another ex- 

 ceedingly important consideration has been overlooked by 

 Dr. Croll, viz. the very great difference of continent and 

 ocean in the matter of temperatures, the fact that an equal 

 loss of heat, expressed in calories, will have a very different 

 influence on temperatures, both on account of the great 

 caloric capacity of water and of the mobility of its particles. 

 I must add that the latter condition is too often lost sight 

 of, not only by Dr. Croll, but by many other scientists, in 

 their speculations on the influence of a solid or liquid sub- 

 stratum on the distribution of terrestrial temperatures. 



Besides, we have the formation of ice on the waters, which 

 also has a great influence on the temperatures. 



Thus it is easy to see, that the question how great will be 

 the temperature of the air at a given place, say in midwinter, 

 when the distance of the sun is greater or less than at present, 

 cannot be answered, even approximatively, especially in the 

 exceedingly crude way in which it is put by Dr. Croll, 

 i. e., without distinguishing high and low latitudes, continent 

 and ocean, &c. One thing is certain, that such a change will 

 certainly have a greater influence on the temperatures in the 

 interior of continents than on the oceans and their borders. 

 The caloric capacity of water is so great, and the mobility 

 of its particles so effectual in resisting a diminution of the 

 surface-temperature (by the convection-currents it causes), 

 that I doubt very much if, during a great excentricity and 

 winter in aphelion, the surface-temperature of the oceans can 

 be lower in winter than now. The difference in the quantity 

 of sun-heat is too small and too fleeting to give an appre- 



