November 14, 1901] 



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than geographical causes. According to M. Eug. 

 Dubois' one obscure enigma is that relating to the 

 glacial episode which has been recognised in parts of 

 India, Australia and South Africa in Permo-Carboniferous 

 times. In those subtropical regions the debris from 

 snow-clad mountains had been able to reach sea-level 

 and be commingled with organic remains of almost 

 tropical character. Other evidence, however, tends to 

 show that there was no general lowering of temperature 

 in this ancient epoch, but that there must locally have 

 been mountains of considerable altitude, and that 

 meteorological conditions were favourable to the develop- 

 ment of huge glaciers. .So also in the case of the far 

 earlier pre-Cambrian period, during which it is believed 

 that glaciation occurred. In connection with the phe- 

 nomena M. Dubois discusses the evolution of the sun 

 and the various influences affecting radiation of heat, 

 maintaining that the general evidence of higher and 

 more uniform temperature over the earth's surface prior 

 to middle Tertiary times is well established, and is not 

 interfered with by evidences of extensive though re- 

 stricted glaciation. 



In drawing attention to the influence of winds upon 

 climate during the Pleistocene epoch Uliiart. Journ. 

 Geo/. SoC; .August 1901 1, Mr. F. \V. Harmer has opened 

 up inquiries of considerable and far-reaching interest. 

 Remarking that seasons abnormally warm or cold, rainy 

 or dry, may be caused by the prevalence of particular 

 winds, though the course of the oceanic circulation re- 

 main the same, he justly remarks that permanent altera- 

 tions would equally result were the direction of the 

 prevalent winds permanently changed. 



Having attentively studied the causes and influence of 

 areas of high and low pressure, he concludes that the 

 climate of the northern hemisphere could not have been 

 wholly cold during any part of the Pleistocene epoch, and 

 that consequently the period of maximum glaciation in 

 North America could not have coincided with that which 

 affected the British Isles. 



Regions covered by ice would have been to a greater 

 or less extent anticyclonic at all seasons, low pressure 

 systems prevailing elsewhere. The northerly winds on 

 one side, either of a cyclonic or an anticyclonic centre, 

 are the necessary equivalent of the southerly winds on 

 the other, the direction in the northern hemisphere in 

 the case of the anticyclone being like that of the hands of 

 a watch, and in the case of a cyclone in the opposite 

 direction. 



Thus the eftect of the anticyclone of an ice-sheet ex- 

 tending eastward from Greenland, over Great Britain, 

 Scandinavia, and Northern Europe, would have been to 

 change the prevalent alignment of the low-pressure 

 system of the North Atlantic, producing warm south- 

 easterly winds in Labrador and New England during the 

 winter, instead of the northerly winds now prevalent 

 there. The alteration in the direction of the winds would 

 have tended, moreover, to divert the warm surface- 

 currents of the North Atlantic from the European to the 

 American coast. 



It is admitted by Mr. Harmer that the maximum 

 glaciation of Great Britain could only have taken place 

 at a time when the Icelando-British channel was closed, 

 either by an elevation of the submarine ridge connecting 

 those countries or by its lieing blocked with ice. Thus, 

 although the winds have naturally a most powerful 

 influence, which he has done good service in pointing out, 

 he is led to consider that to differential earth-movements 

 of elevation and subsidence in different parts of the 

 northern hemisphere may have been due the sug- 

 gested shifting of glacial conditions from one side of the 

 Atlantic to the other, and the alternation of glacial and 

 interglacial periods in the eastern and western continents. 



1 * ' Les Causes probables du Phenomene paleoglaciaire permo-carboniferien 

 dans les basses latitudes." Archh'es Teyier, vii.. Partie 4. (Haarlem, 1901.) 



NO. 1672, VOL. 65] 



In this way the milder periods which locally prevailed at 

 intervals during the Pleistocene epoch would be attributed 

 to meteorological and geographical rather than to 

 astronomical causes. 



ANIMAL PHOTOGRAPHY} 



THE advantages of photography as compared with 

 wood-engraving for the illustration of works on 

 natural history are in many ways so great that any 

 attempt to perfect and popularise the methods in use 

 should be heartily welcomed. Quite apart from artistic 

 effect, the great superiority of photography is that it 

 ensures absolute accuracy, and, when living animals are 

 the subjects, shows them in natural attitudes. In wood- 

 engraving there are several sources of error which only too 

 frequently make themselves apparent. In the first place, 

 the draughtsman may make a blunder. But too often it 

 is the engraver who is in fault, very frequently from 

 mistaking the nature of some feature in the drawing he 

 has to reproduce. For example, the author of the 

 volume before us calls attention to a curious engraver's 

 error in a well-known popular work, where, from some 

 misconception, the mouth of a stickleback appears in a 

 totally wrong position. 



Sui-h errors are, of course, impossible in photooraphs 

 and ])lii)to-i-,i\ ures. Xtnei-tlielL--^, |il)nt(._;i,i|>hv has 



Fig. I.— Hedgehog. 



certain disabilities of its own in regard to animal por- 

 traiture. A trained zoological draughtsman, whose 

 object should be to produce a characlei-istic rather than 

 an arlistic picture, always takes care to draw his subject 

 in a position which will show to the best advantage its 

 distinctive features, whether of form or colour, and for 

 this purpose he generally consults the specialist for whom 

 the sketch is undertaken. The photographer, on the 

 other hand, is usually content to " snap " the animal he 

 has in hand in any effective pose, with the too frequent 

 result that his picture, from a zoological point of view, 

 has comparatively little value. That is to say, the 

 features by which alone the affinities of the animal can 

 be decided are either not shown at all, or are but im- 

 perfectly displayed. 



One of the main objects of the present work appears to 

 be to instruct photographers how to avoid these effects 



1 " Photography for Naturalisls." By D. English. Pp. 132. Illuitrated. 

 (London ; lliffe, 1901.) Price 5s. net. 



