May 6, 1922] 



NA TURE 



573 



unsolicited confession of Major Weir, who was burned 

 as a witch at Edinburgh in 1670. The evidence on this 

 point would not be strong in itself, if it were not fully 

 in keeping with Miss Murray's view of the witch-ritual. 

 As is well known the central features of the Sabbath 

 were a feast and sexual licence. This suggests in- 

 evitably that it was a fertility rite of the type familiar 

 to anthropologists. It was only at a later date, and in 

 the first instance by popular perversion that the function 

 of the witch became the blasting of crops and herds as 

 set forth in the famous Bull of Innocent VIII. 



Many other topics are discussed in this important 

 study which are of the greatest interest to anthropolo- 

 gists, and it bristles with points which call for further 

 consideration did space allow. It has, however, one 

 aspect to which reference must be made, and that is 

 its bearing upon mediaeval history. From this point of 

 view it is a book which no historian or student can 

 afford to neglect. The position of the Church and its re- 

 lation to witchcraft before the beginning of the fifteenth 

 century must be reconsidered first in the light of Miss 

 Murray's conclusions and, secondly, with reference to 

 the numerical strength the cult could command as an 

 organisation — a point upon which Miss Murray does 

 not touch. 



The Riddle of Bird Migration. 



Die Rdtzel des Vogelzuges. Ihre Losung auf experi- 

 mentellem Wege dutch Aeronautik, Aviatik und 

 Vogelberingung. Von F. von Lucanus. Pp. viii + 

 226. (Langensalza : H. Beyer und Sohne (Beyer 

 und Mann), 1922.) 30 marks. 



-^T^HE migration of birds remains one of the most 

 JL tangled problems, as it is one of the greatest 

 marvels of the zoologist's world. In the old days known 

 facts were few and hypotheses were correspondingly 

 simple (and as a rule erroneous), but with multiplicity of 

 data, theories, guesses and suggestions have so increased 

 in number and complexity that they form in themselves 

 a new problem for the seeker after truth. In the 

 matter of precision of data the present generation 

 holds a great advantage over its predecessors. 



The institution of bird-ringing in Denmark by 

 Moitensen in 1899, and its subsequent development in 

 Germany by Thienemann and others, and in this country 

 by the University of Aberdeen and Mr. Witherby, 

 raised hopes of an early solution of many difficulties ; 

 while the development of air-craft and of their use in 

 bird-watching, in which von Lucanus himself was a 

 pioneer, has led to information which appeared once 

 to be beyond man's grasp. 



NO. 2740, VOL. 109] 



In the light of the results of these new methods, von 

 Lucanus restates the problems of the origin and causes 

 of migration, of its direction, height and speed, of its 

 meteorological relations, and, most subtle of all, of the 

 pathfinding of the birds, and re-examines the solutions 

 which have been suggested. It may be said at once 

 that there are here many new facts, and that in many 

 respects the work of the former generation of observers 

 has been superseded ; but with it all, the reader is left 

 with the feeling that while precision has been gained in 

 problems of observation, the great problems of inter- 

 pretation remain still beyond ken. Time after time the 

 author is driven back for explanation upon an incom- 

 prehensible " migratory instinct " or " impulse " 

 (Zugtrieb). Thus, having rejected, on account of their 

 inadequacy as imminent causes of autumn migration, 

 the fall of temperature, the shortening of the day, the 

 lack of food, the changed atmospheric conditions due 

 to the passing of the summer solstice, he concludes, " a 

 bird departs as soon as the time for its departure has 

 coine and the migratory impulse has been awakened, 

 without requiring any particular external stimulus.' 

 Or again, having found tradition, warmer zones, anti- 

 cyclonic conditions, wind guidance, a supposed magnetic 

 sense, power of vision, each and all insufficient to 

 account for the orientation of a bird's migratory flights, 

 he says, " on its journey a bird requires no particular 

 guidance, but follows an instinct which decides the 

 direction automatically." 



Von Lucanus has long been recognised as the 

 champion of migration at comparatively low levels in 

 the air, as against the idea of high-level migration which 

 Gatke made popular. Many observations by airmen 

 have been added to his early balloon observations, and 

 he still regards the general height of migration to be 

 under 400 metres, and flight at 1000 metres or over to 

 be exceptional. Many records support his view, but 

 conflicting evidence involves us in difficulties, for the 

 author makes no mention of the observations of such 

 of our airmen as Capt. CoUingwood Ingram, who saw 

 a flock of five hundred geese or ducks at about 11,500 

 feet, cranes (possibly) at 15,000 feet, birds resembling 

 linnets at 10,000 feet, sandpipers at 12,000 feet, and so 

 on. {Ibis, 1919, p. 321-5.) 



The riddle of migration is not solved, but this volume, 



rich in observations and analyses, gives an excellent 



synopsis of the present state of knowledge, and points 



the way for future research. We may express the hope 



that the German bird-watching stations, disorganised 



owing to post-war conditions in Germany, may soon be 



able to resume their activities and add to the vast 



contributions they have already made to a fascinating 



study. 



J. Ritchie. 



U I 



