58 



NATURE 



[September g, 1920 



ture, consisting of botanists from each of the four 

 provinces, with the chief of the division of botany 

 and plant pathology as director of the Survey. The 

 botanists comprising the Committee are each in 

 charge of different administrative areas into which 

 the Union has been divided for purposes of the 

 Survey. It was agreed that as a basis of the Survey 

 the preparation of regional floras should be taken in 

 hand and local vegetation surveys prepared, and the 

 present contribution is the first of these regional floras. 



Prof. J. C. Branner has furnished a much-needed 

 summary of the geology of Brazil, together with a 

 coloured map on the scale of i : 5,000,000 (Bull. Geol. 

 Soc. America, vol. xxx., p. 189; second ed., April, 

 1920). The included bibliographies enable the reader 

 to supplement on any special line the immenie amount 

 of material here brought together in a condensed form 

 from the author's own experience. Among the plates 

 is a handsome photograph of a striated boulder from 

 the Permian beds of Sao Paulo. 



Mr. H. p. Whitlock {kmer. Journ. Sci., vol. xlix., 

 p. 259, 1920) has constructed and described a model 

 for the demonstration of any point-system in atomic 

 spacing within crystals, the atoms being represented 

 by perforated wooden beads, which are obtainable 

 in six colours from dealers in kindergarten requisites. 

 Glass rods are used for their support, and these are 

 passed through holes appropriately punched in two 

 horizontal plates of tin set in a frame. Only two 

 types of frame are required by the crystallographic 

 systems. 



We know, from such valuable publications as Collet's 

 " Alpes calcaires entre Arve et Rh6ne," that geology is 

 honoured by the Sociiti de Physique et d'Histoire 

 Naturelle de Geneve. In the Compte rendu des 

 sdances for April to July, 1920, various authors discuss 

 such topics as details of Alpine structure ; the 

 glacial origin of the Petit Lac of Geneva, involving 

 the question of the capture of the Rh6ne Valley ice 

 by the Arve basin, and the end of the struggle between 

 the Arve and Rhine for the possession of the waters 

 of the upper Rh6ne; the green rocks of the southern 

 Urals (to which M. L. Duparc brings his experience) ; 

 and the classification of felspar twins, by M. R. Sabot. 

 It is clear that geologists must keep even the minor 

 publicatifins of this society within their scope. 



Captains and officers of vessels traversing the North 

 Atlantic will find much of value and interest to them 

 in the series of " Monthly Meteorological Charts " 

 issued by the Meteorological Office. The chart for 

 September gives the distribution of winds and ocean 

 currents at this season of the year, and the mean 

 values of the barometer are indicated by isobars over 

 the sea as well as over the adjacent land. Mean 

 temperatures of air and sea surface are also given. 

 The normal conditions show a large area of high baro- 

 meter readings centred in mid-Atlantic, around which 

 there is a general circulation of winds. A smaller 

 region of high barometer embraces New York and 

 the neighbouring land and sea. Areas of low baro- 

 NO. 2654, VOL. 106] 



meter occur to the south of Greenland and near the 

 equator, as well as over North America and Central 

 Africa, all of which materially influence the normal 

 wind circulation. The extension of the " Gulf Stream " 

 is very evident on the eastern side of the Atlantic to 

 as far as 50° or 55° N. latitude. The southern limit 

 of the north-east trade, and the northern limit of the 

 south-east trade, winds embrace an area centred in 

 about 10° N. latitude. On the reverse of the chart a 

 brief description is given of the different types of 

 atmospheric systems which produce certain and dis- 

 tinct kinds of weather, and illustrations are given 

 which will be helpful to the navigator in constructing 

 a weather chart for himself with the aid of wireless 

 reports he may receive. 



The Meteorological Magazine for August shows that 

 every effort is being made to improve the Daily 

 Weather Report. Sea- and air-temperatures and the 

 weather in home waters are now incorporated, whilst 

 since August i a small map is given showing "baro- 

 metric tendency " for the three hours from 4h. to 7h. 

 For the special advantage of aeronauts a method of ' 

 obtaining the degree of visibility on cloudy nights is 

 suggested by Capt. W. H. Pick. The use of the 

 grease-spot photometer of Bunsen is advocated, cali- 

 brated in accordance with the visibility-scale adopted 

 by the Meteorological Office and allied authorities. 

 The apparatus consists of a drop or two of molten 

 grease on a sheet of writing paper and a candle placed 

 behind the grease spot. The observer faces the spot 

 and moves backward, noticing the exact position at 

 which the spot of grease becomes indistinguishable on 

 the paper. The distance of indistinguishability in feet is 

 given in a tabular form for the respective units of the 

 visibility-scale. Careful examination of the suggestion 

 by independent workers is desirable before its final 

 adoption. At best it seems that the method must be 

 rough. July is stated to have been generally a wet 

 month over the British Isles, and the Thames Valley 

 rainfall map shows some areas having a fall of mor« 

 than 6 in. The general July rainfall for England and 

 Wales was 161 per cent, of the average, Scotland 

 104 per cent., and Ireland 153 f>er cent. 



It has long been known that the sensitiveness of 

 photographic bathed plates can be increased by the 

 addition of ammonia to the dye-bath, though at the 

 expense of keeping qualities and freedom from 

 chemical fog. Mr. S. M. Burka has critically studied, 

 at the American Bureau of Standards, the action of 

 ammonia on commercial plates, hoping thereby to 

 increase their sensitiveness and facilitate aerial photo- 

 graphy. His communication to the Franklin Institute 

 on the subject is reproduced in the British Journal of 

 Photography for August 6, 13, and 20. He finds that 

 ordinary and orthochromatic plates are not much, if 

 at all, affected by bathing them in weak ammonia, 

 but panchromatic plates may be increased in sensitiva- 

 ness to as much as five times. More usually the in- 

 crease is to about twice, but even then the sensitive- 

 ness to red may be increased to five times and be 

 extended 100 or more Angstrom units. Plates 



