























Apri 14, 1923] 
> 
MIGRATIONS OF THE WaAxwinc.—The waxwing, 
Ampelis garrulus, is not a rare visitor to our shores. 
_ Seldom a winter passes but one or more is observed in 
eastern parts of Britain, and occasionally its numbers 
indicate a very considerable immigration. The 
_ largest ever witnessed in Scotland occurred in the 
late autumn of 1921, and is discussed by Dr. J. Ritchie 
in the Scottish Naturalist, September 1922—February 
1923. The immediate cause of Scotland’s share in 
_ this immigration is due in the first place to the lack~ 
_of food-supply in Norway. The summer of 1921 in 
that country has been notorious for the lack of wild 
berries upon which the waxwings feed. Large flocks 
of the birds congregated in the southern part of 
Norway, but, finding insufficient food, took advan- 
tage of easterly winds accompanied by a rapidly 
rising barometer to reach our shores. The meteor- 
ological phenomena associated with the migration 
are complex, and Dr. Ritchie promises to deal with 
them in a future paper. 
' BoranicaL SuRVEY AND EcoLoGy IN YORKSHIRE. 
—Under this title a most valuable and comprehensive 
account of the development of our knowledge of the 
Yorkshire flora is given by Dr. T 
W. Woodhead in the Naturalist for 
March 1923. The first flora of 
Yorkshire was published at Halifax 
in 1840 by Henry Baines, and since 
then the three Ridings have been 
more intensively dealt with in the 
three well-known floras, Baker’s 
“North Yorkshire,’ Arnold Lee’s 
“Flora of. West Yorkshire,” and 
Fraser Robinson’s “ Flora of the 
East Riding of Yorkshire.’’ Many 
other valuable systematic works 
dealing with the Yorkshire flora 
are described by Dr. Woodhead, 
who then proceeds to narrate the 
development of botanical survey 
and the mapping of plant associa- 
tions, under the inspiration of the 
brothers Robert and William G. 
Smith. Around these men an active 
band of workers gathered, and 
in December 1904 the Central Committee for the 
Survey and Study of British Vegetation was formed | 
at a meeting held at the house of Dr. W. 
G. Smith in Leeds; in 1t913 this Committee was 
replaced by the British Ecological Society with its 
wider membership. Two vegetation formations that 
have been extensively studied in Yorkshire are the 
woodlands and the moorlands, and Dr. Woodhead 
briefly traces the development of our knowledge of 
these characteristic vegetation features, their distribu- 
tion, development and occasional retrogression. 
There is an interesting discussion of the significance 
of the vegetation found in the peat of the Southern 
Pennines, and the bearing that the studies have upon 
persistence of the flora from pre-glacial times. Dr. 
Woodhead’s work upon the relation of vegetation 
survey to the many other activities and interests of a 
district was well illustrated by the extraordinarily 
interesting series of maps of the Huddersfield area 
that were on view in Hull during the British Associa- 
tion meeting, in the exhibition room of the Yorkshire 
Naturalists’ Union. Jt is therefore natural to find 
that the presidential address to the Yorkshire Natur- 
alists’ Union closes with the expression of a hope that 
_ such ecological studies may extend to man, and that 
NATURE 

A—Ordinary contour map. 

the local museum may enshrine the results of an 
NO. 2789, VOL. 111] 

511 

Research Items. 
intensive local survey of plant and animal, including 
human communities. 
A NEW PROCESS FOR MAKING STEREOSCOPIC Maps.— 
A paper read at a recent meeting of the Paris Academy 
of Sciences (Comptes vendus, January 22) described a 
new method, due to M. G. Poivilliers, for obtaining 
stereoscopic maps. The various methods proposed 
hitherto have been based on the use of two conical 
perspectives, the production of which involves prac- 
tical difficulties; in M. Poivilliers’s method two 
cylindrical projections are used, one vertical and the 
other oblique. Referring to the accompanying illus- 
tration (Fig. 1), the projection A is an ordinary contour 
map ; the projection B is obtained from A by shifting 
the contour lines in the direction east-west by an 
amount proportional to their altitude above an 
arbitrarily chosen datum line. The resulting stereo- 
scopic view shows theoretically a slight curvature 
effect which, however, does not alter the relative 
relief. In examining with a stereoscope even the 
above reproductions, the result obtained is very 
striking. The ‘‘ falsified ’’ map B was in this case 
drawn by hand with the aid of a tracing of A, but it 
NS \ 
R77 
-. 
SS 
WSS 

Fic. t. 
B—Complementary map, with contour 
lines displaced. 
is easy to imagine a simple apparatus by means of 
which this can be done semi-automatically. The 
contour interval is in this case 20 metres, and corre- 
sponds to a horizontal shift of 0-5 mm. It is antici- 
pated that M. Poivilliers’s method, on account of its 
simplicity, will tend to generalise the use of stereo- 
scopic maps, especially for purposes of instruction in 
topographical surveying. It has also been suggested 
that the process could be usefully applied to geological 
maps, by making it possible, for example, to visualise 
the superposition of successive layers inside the earth. 
ATMOSPHERIC HUMIDITY IN THE UNITED STATES =~— 
Prof. R. de C. Ward, of Harvard University, is the 
author of a communication on the above subject in 
the U.S. Monthly Weather Review for November 1922. 
The communication is admirably illustrated with 
diagrams ; two are given for January, at 8 a.m. and 
8 p.m., and two for the corresponding hours in July, 
showing the relative humidity by lines of equal 
value over the whole of the United States. The 
element is a real and definite factor in climate, and 
especially affects our bodily comfort. The values 
give the ratio between the amount of moisture in 
the atmosphere and the amount which could be 
present without condensation. On the Pacific, 
