Makch 23, 1883.; 



SCIENCE. 



193 



miiiishes with the lowering of temperature, 

 Professor Whitney conceives that a general 

 lowering of terrestrial temperature by reason 

 of the dissipation of solar energy will make 

 the arid regions of the earth more arid ; and 

 he therefore cites the drying-iip of rivers and 

 lakes in regions alreadj' exceedingly dry as 

 evidence of a general lowering of temperature. 

 Bj' approaching the subject from a different 

 side we may reach a verj^ different conclusion. 



If terrestrial warmth, instead of emanating 

 from a single celestial bodj', were due to an 

 equable radiation from the whole sphere of 

 space, there would be no atmospheric circula- 

 tion. The whole air would be saturated with 

 moisture, and the whole surface of the earth 

 would be wet ; but there would be no precipi- 

 tation, no evaporation, no streams. We may 

 therefore consider saturation the normal or 

 static condition of the air, and wetness the 

 normal condition of the land. The actual ine- 

 quality of extraneous radiation — the relative 

 intensity of solar radiation — is a disturbing 

 factor. It produces atmospheric circulation, 

 therebj' causing precipitation, and diminishing 

 the humidity' of the atmosphere so that evapo- 

 ration becomes possible. Precipitation is the 

 necessary condition of evaporation. Hy pre- 

 cipitation and evaporation, inequalities are in- 

 troduced in the distribution of moisture upon 

 the surface of the land. Where precipitation 

 preponderates, the condition becomes moister 

 than the normal ; where evaporation prepon- 

 derates, it becomes drier. Excessive aridity, 

 therefore, as well as excessive humidit}-, is 

 caused b}' solar heat ; and everj' increase of 

 solar radiation tends to magnify the contrast 

 between moist regions and Ary regions, mak- 

 ing the moist moister and the dry drier. 



If our author has fallen into error in his fun- 

 dam^ental postulates, we need not be surprised 

 to find that facts have proved stumbling-blocks 

 to him, and that he has involved himself in 

 numerous inconsistencies. It will be profitable 

 to call attention to some of these. 



On p. 341 he asserts that the recession of 

 the glaciers of the Alps is part and parcel 

 of a general phenomenon of desiccation ; and 

 this desiccation his theory ascribes to a gen- 

 eral lowering of temperature. On pp. 240 

 and 296 he notes as evidence of this same 

 lowering of temperature the extension of gla- 

 ciers in Iceland and the increased abundance 

 of icebergs in the north Atlantic. Thus the 

 extension of glaciers in one region, and their 

 shrinkage in another, are both assigned to the 

 same degradation of climate. 



Having asserted that the phenomena of the 



glacial epoch in Scandinavia had their origin 

 in local causes, and that the cognate phenom- 

 ena, not onlj' in the Alps, but in the Pyrenees, 

 the Vosges, and the Caucasus, were part of 

 the same sj'stem of events, he nevertheless 

 declares that the ancient glacial phenomena of 

 the Himalaya, of New Zealand, and of the 

 Sierra Nevada, are not of sufficient importance 

 to call for special explanation. And yet the 

 glaciers of the Himalaya and New Zealand 

 have shrunk, since their greatest extension, 

 more than those of the Caucasus and Pyrenees ; 

 and the system of glaciers that has disappeared 

 from the Sierra Nevada was greater than that 

 ascribed to the Vosges. If the lesser changes 

 are worthy to have a cause assigned them, why 

 should the greater be ignored ? 



It is stated that the precipitation on the 

 Sierra Nevada was very great in tertiary time, 

 and has since continuously diminished. At a 

 very late geological date the vallej^s of the 

 range were occupied bj' glaciers ; and the ex- 

 planation given is, that the precipitation was 

 greater then than now. But no suggestion is 

 offered in explanation of the fact that at an 

 earlier period, when the precipitation was still 

 heavier, there were no more glaciers than at 

 present. 



This instance maj^ be classed with a number 

 of others, in which phenomena consistent with 

 his theory are looked upon as sj'stematic, while 

 those of an opposite character are regarded as 

 temporary or unimportant. The rise of the 

 lakes of the Great Basin, since the first obser- 

 vations thirty-five j^ears ago, appears to him 

 a temporarjr oscillation ; but the fall of the 

 Lake of Valencia during a period of fifty years 

 is made one of the proofs of a general desic- 

 cation, and the subsequent rise of the same 

 lake does not find mention. The recent reces- 

 sion of the glaciers of the Alps is referred to 

 a secular and general cause ; but the contem- 

 poraneous advance of the glaciers of Spitz- 

 bergen is assigned a local cause, while the 

 advance of the glaciers of New Zealand is 

 ignored. The semi-periodic blocking of the 

 Rofenthal by ice is mentioned as a curious 

 anomalj', apparently without any realization 

 that it points to a substantial uniformity of 

 mean conditions for a period several times 

 longer than that of the glacial recession upon 

 which stress is laid. 



One of the most curious features of the book 

 is its assumption of the possibility of detecting 

 evidence of a secular change of climate within 

 the brief period of human histor}'. To one 

 who has the geologist's conception of geologic 

 time the idea is so extravagant as to be fairly 



