54 



NATURE 



[January 12, 1922 



origin of the cliief physical features. A short account 

 of the distribution of the geological formations is also 

 given, and this is followed by a section which 

 describes the roads and railways of the district in 

 their relation to the surface relief. The pamphlet 

 should prove indispensable to those students and 

 teachers of geography and geology who have access 

 to the model. 



From the " Report on the Zoological Service for the 

 Year 1920 " we learn that the Giza Zoological Gardens 

 have been restored to their pre-war condition of 

 cleanliness. The number of visitors during that 

 year was greater than in any previous year. A special 

 feature of these gardens is the thousands of birds in a 

 state of complete liberty which frequent the grounds, 

 and we are glad to note that the numbers of cattle 

 egrets, little egrets, and hoopoes which have nested 

 there are increasing. The new building of the Giza 

 Zoological Museum was opened in 1920. Lack of 

 space and insufficiency of staff, however, will prevent 

 the development of a general natural history museum. 

 The insect collections have already been transferred 

 to the Ministry of Agriculture and the marine inverte- 

 brates to the Sultana Hydrobiological Institute. The 

 Zoological Service of Egypt is doing a useful work in 

 the preservation of the natural fauna of the country 

 both by protecting game and nesting birds and by con- 

 trolling beasts of prey. Special success has attended 

 its efforts to protect birds from the birdlimers, to 

 preserve the breeding colonies of the cattle egrets, 

 and to keep down the number of jackals. 



An interesting addition to the flowering plants of 

 the British flora is announced in the November issue 

 of the Naturalist. Mr. R. W. Butcher found Tillaea 

 aquatica at Adel, near Leeds, in September, where it 

 was the dominant plant growing in abundance on the 

 drying-up mud on the margin of a pool. Dr. G. C. 

 Druce has examined the plant, and agrees that it is 

 probably a true native species or one brought there 

 by purely natural means. The typical plant is known 

 from Germany, and a sub-species also occurs in France 

 and Italy. 



The December issue of the Journal of the Franklin 

 Institute contains a paper by Mr. Enoch Karrer, of 

 the Nela Research Laboratories, Cleveland, Ohio, on 

 the shape assumed by a deformable body immersed 

 in a moving fluid. The author's attention was 

 directed to the subject by the behaviour of a drop of 

 mercury just above a constriction in a vertical glass 

 tube up which a current of gas was flowing. As the 

 speed of the gas was increased the drop was raised 

 above the constriction and assumed a slightly egg- 

 shaped form with its larger end downwards. With 

 increase of speed it elongated, keeping its larger end 

 downwards, and finally a small drop detached itself 

 from its upper end. From these observations the 

 author concludes that a deformable body in a moving 

 fluid assumes a stream-line shape. He supports his 

 conclusion by figures of snow drifts and snow bosses 

 from Cornish's "Waves of Sand and Snow," of egg- 

 shaped boulders with their long axes in the direction 

 of the wind and their big ends up-wind, and by the 

 NO. 2724, VOL. 109] 



shapes of moths, birds, and fishes. By analogy with 

 " geotropism "^ — the adjustment of organisms under 

 gravity — the author proposes to name this new prin- 

 ciple "rheotropism." 



The Meteorological Oftice of the Air Ministry has 

 recently issued as No. 18 of the Geophysical Memoirs 

 a memoir by Mr, W. H. Dines on observations on 

 radiation from the sky and an attempt to determine 

 the atmospheric constant of radiation. The measure- 

 ments were made at Benson during 1920. The sky 

 was divided into, six zones of 15° width, and the 

 radiation was taken at the altitudes corresponding 

 to the. mean altitude of the zones. The final form 

 of instrument used was a thermopile of copper-eureka 

 junctions designed by L. F. Richardson, The observa- 

 tions were made at, or a little after, sunset, and are 

 classified under "clear sky," "overcast sky," and 

 "very clouded sky," By suitable methods the amount 

 of radiation received from each zone on a hori- 

 zontal surface at ground-level is calculated, and 

 the final results show that the average daily supply 

 of heat from the atmosphere throughout the year 

 falling on one square centimetre in the South of 

 England on clear days is 506 gram calories. For fully 

 clouded skies the value is about 700, with a general 

 mean for all days of about 600. For a mean tem- 

 perature of 50° F. the outward radiation from the 

 earth is 711 gram calories, so that the net or effective 

 radiation for a clear sky is rather more than 200 gram 

 calories. This is 25 per cent, less than the values 

 usually given, which, however, have been mostly 

 obtained at much greater altitudes than Benson 

 (186 ft. above sea-level). 



The commercial transmission of power conveyed 

 electrically by overhead wires has made the study 

 of lightning arresters of great importance. In places 

 where thunderstorms are violent, such as in certain 

 parts of South Africa or where the lines have to 

 traverse mountainous regions, the use of efficient 

 lightning arresters is a necessity. In this connection 

 the papers published in the General Electric Review 

 for November and December last by J. L. R. Hayden 

 and N. A. Lougee are of value. The object of 

 lightning arresters is to afford protection against 

 sudden rushes of electricity at high potential in the 

 lines due to atmospheric disturbances. To get similar 

 electric surges in the laboratory they build up a 

 battery of glass-plate condensers which by means of 

 the kenotron (a two-electrode thermionic valve for 

 rectifying currents of high voltage) can be charged by 

 an alternating-current transformer to 30,000 volts ; 

 200 of these condensers are used, which can be con- 

 nected in parallel or in two groups of 100 in parallel 

 or in four groups of 50 in parallel. When they are 

 all in parallel the capacity is i-6 microfarads, and at 

 30 kilovolts the energy stored is 720 joules. With 

 the arrangements they used they got a maximum 

 discharge of 9500 amperes at 120,000 volts, the dis- 

 charge frequency being 126,000. Three types of 

 lightning arrester were examined : (i) the horn type 

 with resistance in series, (2) the electrolytic type, and 

 (3) the multigap type. Their results prove that the 



