68 



NA TURE 



[July 14, 1923 



and discrimination between the beds involved, and 

 zoning would have been facilitated accordingly. 

 Authigenous constituents of sediments vary qualita- 

 tively and quantitatively within small limits far 

 more than the more stable detrital grains do, and 

 for this, if for no other reason, the study of the 

 " heavy " minerals is always desirable. Notwith- 

 standing the neglect of these constituents, however, 

 the authors have grouped their samples into ten 

 zones, comprising parts of the Tertiary and Upper 

 Cretaceous formations in the district ; such zones 

 are of incalculable value to the drillers and others 

 engaged in exploring the field, but it would be 

 interesting to know how far such zones were con- 

 firmed or contradicted by similar work based on 

 ' heavy " mineral assemblages. 



Braciiystegia, a Tropical Source of Fibre 

 AND Timber. — Messrs. J. Burtt Davy and J. Hutchin- 

 son describe fifty-four species of Brachystegia in the 

 Kew Bulletin, No. 4, 1923. This genus is confined 

 to equatorial Africa, and is so dominant in the vast 

 forest area extending between the Limpopo Zambesi 

 watershed and the Katanga Plateau at the head 

 waters of the Congo River, and from Nyasaland to 

 the Angola Highlands, that this plant formation 

 might well be termed " Brachystegia Forest." All 

 species are trees with fibrous bark, sometimes con- 

 taining tannin, and the natives of Central Africa 

 use this bark for an extraordinary variety of purposes. 

 Brachystegia bark cloth is used for making grain 

 sacks and game nets, the fibres of some species being 

 used for the manufacture of cord and rope of all 

 sizes and for all purposes. Before the widespread 

 introduction of cotton goods, the principal clothing 

 of the native was bark cloth made of fibrous sheets 

 beaten out of the bark of several species of Brachy- 

 stegia. The timber of some species is described as 

 hard and durable and suitable for building purposes, 

 that of others as too soft. Undoubtedly both 

 fibrous bark and timber may have many industrial 

 applications, but the first step towards economic 

 development is a clear idea of the different species 

 of the trees and their different possibilities. To this 

 end the taxonomic study in the Kew Bulletin should 

 have great value, as one of the autjiors has studied 

 the plants in their native habitat and a first attempt 

 is made to indicate what different species are probably 

 intended by the vernacular names used by the natives. 



Liberation of Prussic Acid from the Plant 

 Leaf. — The highly toxic properties of hydrocyanic 

 acid have caused the accumulation of a considerable 

 literature upon the subject of its production in 

 plant tissues from cyanogenetic glucosides under 

 various conditions. The problem is obviously not 

 simple, and, as occasional cases of stock poisoning 

 are traced to this source, its study has economic as 

 well as scientific interest. F. J. Warth has recently 

 studied the liberation of prussic acid from the tissues 

 of the Burma bean {Phaseolus lunatus), and supplies 

 some very interesting data in the Memoirs of the 

 Department of Agriculture in India (Chemical Series), 

 vol. vii. No. I. He points out that the amount of 

 prussic acid produced differs materially according to 

 whether the leaves are dried rapidly in the sun or 

 slowly in the shade. In the sun-dried leaf, hydrolysis 

 takes place with evolution of prussic acid, and if the 

 dried leaf be plunged into boiling water further 

 large amounts of the acid are given off ; this etfect 

 is not produced with the fresh leaf or slowly-dried 

 leaf. It appears that in the slowly dried leaf the 

 enzymic balance approximates to that in the normal 

 leaf, and in this balanced system prussic acid appears 

 to be further changed as rapidly as it is released by 



NO. 2802, VOL. I 12] 



enzymic hydrolysis of the glucoside ; indeed, both 

 fresh leaf and slowly dried leaf show some capacity 

 to cause the disappearance of additional acid, if 

 added to water containing the crushed or powdered 

 leaf material. 



Short-Wave Directive Radio Transmission. — 

 Franklin and Marconi have shown that when the 

 wave-lengths used in radio transmission are less 

 than 20 metres it is not difficult to get directive 

 transmission. For transmitting news and music, 

 broadcast directive transmission is not wanted, but 

 for broadcast reception it can be usefully employed, 

 as by its means interference disturbances may be 

 reduced to a minimum. Its principal use is in 

 connexion with point-to-point communication, i.e. 

 direct communication from one transmitting to one 

 receiving station. In particular it will be useful in 

 the new methods adopted of transmitting photo- 

 graphs by radio and for the remote control of mechan- 

 isms. In paper No. 469 published by the Bureau 

 of Standards, F. W. Dunmore and F. H. Engel give 

 the results of experiments with directive radio 

 transmission on a wave-length of 10 metres. As a 

 reflector they use a series of forty vertical parallel 

 wires all of which lie on the surface of a parabolic 

 cylinder. It is so mounted that it can be rotated 

 about a vertical axis. The focal length of the 

 parabolic section was made one-quarter of a wave- 

 length, 2 '5 m. (8 feet 2-4 inches). Each of the wires 

 was tuned to 10 metres, and they were spaced 30-47 

 cm. apart. A 50-watt three-electrode valve of the 

 coated filament type was used as a generator. 

 Radiation characteristic curves are given from which 

 it appears that at least 75 per cent, of the radiated 

 power is confined to an angle of 40°. It was noticed 

 that with this type of transmission the absorption 

 by buildings and other metallic structures was very 

 pronounced. 



Weather at Eastbourne in 1922. — Eastbourne 

 Borough Council has recently issued its annual 

 report of the meteorological observations for the 

 year 1922. The records have been kept continuously 

 since 1887, a period of 36 years, so that valuable 

 statistics are available as to the weather and climate 

 of this much-favoured health resort. Observations 

 are supplied to the Meteorological Office and are 

 included in the Weekly, Monthly, and Annual 

 Weather Reports, as well as in the Daily Report of 

 Health Resorts, In addition to the observations at 

 Eastbourne the report comprises similar results for 

 other health resorts scattered over England, taken 

 from the Meteorological Office returns, from which 

 it can be seen that Eastbourne occupies a position 

 with a fairly equable temperature, with a large 

 amount of sunshine, and with a rainfall by no means 

 excessive. The mean air temperature in 1922 ranged 

 from 59-2° F. in August to 41-6° F. in January, and 

 the mean for the year was 49-9° F. The duration 

 of sunshine ranged from a mean of 10-40 hours per 

 day in INIay to 1-76 hour per day in December, the 

 mean for the year being 4-80 hours per day. The 

 mean monthly rainfall for 1922 ranged from 4-31 in. 

 for Januarj^ to o-6i in. for May ; the total for the 3ear 

 was 28-10 in. The prevailing winds were from the 

 west and north-west, though in most recent years 

 the prevailing winds have been from betAveen south- 

 west and north-west. From this prevailing direction 

 the air has to pass over the South Downs before 

 reaching the town, and, mixing with the air over 

 the sea, may often account for a fair amount of fog 

 in the Channel, in the neighbourhood of the Royal 

 Sovereign Lightship, and frequently may render the 

 air somewhat humid over the land. 



