December 29, 1921] 



NATURE 



579 



in temperate countries or on the mountains in lower 

 latitudes, reaching the equator on the mountains of 

 Central Africa and South America. About 500 species 

 are at present known to the botanist. Mr. Praeger 

 has, to the best of his ability, ransacked the gardens 

 of the world, and has received and grown no less than 

 151 species, of each of which he gives a full descrip- 

 tion with a good illustration showing the habit of 

 the plant and structural details of leaf and flower. 

 Of this number only about twenty-seven are usually 

 found in English and Continental gardens, though 

 many of the rarer ones are of considerable interest or 

 beauty. Further, there are great possibilities ; among 

 the many hundreds of new plants described in recent 

 years from China, esf)ecially from the scarcely acces- 

 sible western provinces, are at least ninety new- 

 species of Sedum w-hich are known almost entirely 

 from dried specimens in the herbarium. Mexico, 

 which is now known to be extraordinarily rich in 

 Sedums, was until recent years a terra incognita, and 

 many handsome species are in cultivation at Washing- 

 ton and elsewhere, though almost unknown in Euro- 

 pean gardens. The Sedums are notorious for the 

 ease with which a scrap will take root and grow ; 

 in many species detached leaves will produce a bud 

 and root from their base, which speedilv form a new- 

 plant. They are also very easy to cultivate, and few 

 plants are better fitted to endure adverse conditions of 

 soil and moisture. 



A MAP to show the chief sources of metals in the 

 British Empire w-ith diagrams of production for 1918 

 has been prepared under the direction of the Mineral 

 Resources Committee of the Imperial Institute 

 (Messrs. G. Philip and Son, 55. 6d. net, on paper). 

 The sheet, measuring 35x44 in., contains a map 

 of the world, excluding high latitudes, on Gall's pro- 

 jection, a number of inset maps, and diagrams of out- 

 put for the chief metals and metallic ores. It is 

 executed on a bold scale with a view- to its utilisation 

 as a w-all-map for reference and educational purposes. 

 One striking effect of the diagrams is to make it 

 evident that, except in respect of gold, nickel, and 

 perhaps tin, the British Empire output of no metal 

 amounts to 50 per cent, of the world's output; in 

 many cases the proportion is much lower. It is a pity 

 that the figures for a more normal year could not 

 have been utilised. 



Capt. J. B. L. Noel has recently laid before the 

 Royal Geographical Society some notes from his own 

 experience on the photographic equipment and 

 methods of work for travellers. These notes are 

 offered as an addition to the instructions already con- 

 tained in the society's "Hints for Travellers," and 

 are well worth the study of anyone interested in the 

 subject. For general purposes he advocates a quarter- 

 plate camera, made of metal if possible, but otherwise 

 well brass-bound, as giving better results with modem 

 anastigmats and later enlargement to whole-plate size, 

 than photographs of this size taken direct, wnth a 

 great saving in both portability and rapidit}- of action. 

 The tripod, however, should be as constructed fcH- 

 whole-plate cameras, and may easily Be provided with 

 NO. 2722, VOL. 108] 



an azimuth circle and compass. The lens should be a 

 convertible anastigmat with a between-lens shutter. 

 For special "instantaneous" photography the reflex 

 camera is replaced by. a vest-pocket fixed-focus 

 camera, which is the acme of portability and sim- 

 plicity. The author deals also with orthochromatic 

 modifications, kinematography, and sundry other 

 matters. "Development," he says, "should always 

 be carried out in the field within about fourteen days 

 of exposure, and within six days in tropical countries." 



Long-range forecasts issued officially in the early 

 part of the autumn have, beyond doubt, been most 

 thoroughly appreciated by the general public. The 

 forecasts, issued on -September 26 and 28, scarcely 

 surprised those who have carefully watched the pro- 

 gress made by the Meteorological Office in recent 

 years, although the venture was bold. The Meteoro- 

 logical Magazine for November contains an explana- 

 tion of the long-range forecasts made, and deals with 

 the weather conditions which led to the forecast, 

 giving in detail the weather which followed. The 

 circumstances are set out by Mr. E. V. N'ewnham, • 

 who is engaged in the Forecast Branch of the Meteoro- 

 logical Office. .An anticyclone was centred over the 

 British Isles and low-pressure systems existed over 

 Iceland as w-ell as in Scandinavia and in the neigh- 

 bourhood of the .Azores. The occasions of similar 

 conditions in September were tabulated for several 

 years, and the duration of later fine w-eather was 

 noted for stations in England south of the Mersey 

 and Humber. The time elapsing before the com- 

 plete break up of the fine spell over eastern England 

 was only in one instance less than a fortnight. In 

 the recent September long-range forecasts there w-as 

 a temporary break in the south-we>it in some places 

 on the seventh and eighth days. In ncwthern England 

 appreciable rain fell on the eighth and ninth days. 

 Over eastern and central England south of the 

 Humber a definite break-up had not occurred on 

 October 14. The ten-day forecast issued on Sep- 

 tember 26 for the southern half of the kingdom was 

 not altogether a success, but the fourteen-dav fore- 

 cast for the eastern and central parts of England 

 issued on September 28 was decidedly successful. 

 Beyond doubt similar forecasts will be made in the 

 future as opportunity is afforded. 



"The British Journal Photographic .Almanac'* 

 makes its appearance as usual, and continues to be 

 the indispensable book of reference for all who are 

 in any w-ay concerned with the practice of photo- 

 graphy. The editor has few notable departures to 

 chronicle for the past year. The chief of those men- 

 tioned .is the process of desensitising exposed plates 

 so that development may be carried on in a much 

 brighter light than is otherwise permissible. In the 

 " Epitome of Progress " attention is directed chiefly 

 to practical details, as the more strictly scientific 

 matters are now- being systemarically recorded in 

 • Photographic .Abstracts " prepared by the Scientific 

 and Technical Group of the Royal Photographic 

 Society, We congratulate the editor on his " Histor\' 

 in Brief of Photographic and Photo-mechanical Pro- 



