Recently published Ornithological Works. 343 
is this true of the velocity of the movements of the flocks on 
migration, which Gatke calculates in the case of the Red- 
spotted Bluethroat at some 45 geographical miles per hour. 
This estimate is founded on the belief that the bird quits 
Egypt at the end of April or beginning of May, while it 
arrives in Heligoland at about the same time of year •, so 
that some 400 miles would be covered in one spring night of 
perhaps 9 hours duration. Moreover, Gatke appears to have 
believed that the flocks never, or hardly ever, rested by the 
way. Now Herr Helm is at great trouble to shew that the 
Blue-throat leaves Egypt in February or March, and proves by 
many a record that it occurs in spring much more frequently 
than has been hitherto believed in the intermediate districts of 
Austria and Germany. It therefore has one or two months in 
which to compass the journey. 
Again, as to the height at which the flocks travel, he 
considers that former calculations may have been erroneous, 
for he thinks that the state of the atmosphere has not been 
sufficiently reckoned for, and that it may produce delusive 
effects both upon the eye and the ear of the observer. 
Sound travels very difi^erently through diff'erent media, and 
the distance of a bird may be extremely difficult to judge 
correctly. The second article brings under consideration the 
flight of Swallows, Carrier-Pigeons, and Ducks, with a 
discussion of the effects of temperature. 
57. Hudson's ' Birds and Man.' 
[Birds and Man. By W.H.Hudson, F.Z.S. London. 8vo. Longmans. 
318 pp. 1901. Price 6s. net.] 
This new volume of our friend Mr. W. H. Hudson^s essays 
on topics connected with bird-life will be of interest to 
ornithologists as well as to the world in general. They relate 
to such popular subjects as Daws, Ravens, and Willow- 
Warblers, and to such familiar places as London, Wells, and 
Selborne, but will be none the less appreciated by many of us. 
The Dartford Warbler has deservedly a chapter to itself: 
Mr. Hudson found it still existing in four counties '' in a few 
widely-separated localities,'^ but in spite of the " protection- 
