6io 



NATURE 



[February 5, 1920 



(vol. liv., No. 648). The excess was nowhere large, 

 exceeding lo per cent, only in scattered patches across 

 the southern Midlands, and reaching 20 per cent, 

 apparently only in parts of Leicestershire. North 

 Wales had a 10 per cent, excess, but in South Wales 

 the summer and autumn drought resulted in many 

 places in a 10 per cent, deficiency. Parts of the east 

 and north of Scotland, notably northern Aberdeen- 

 shire and the Orkneys, had more than the average 

 fall, but in central and southern Scotland there was 

 a deficiency culminating in 20 per cent, below the 

 average in central Inverness-shire and Perthshire. 

 .Almost the whole of Ireland had less than the average 

 rainfall, the deficiency being greatest in counties Cork, 

 Gal way, and Kerry, where it reached 20 per cent, 

 below the mean. Taking the British Isles as a whole, 

 the year, although by no means exceptional, was 

 probably the driest since 1908— a result largely due to 

 the shortage of rain in summer and autumn. 



Col. J. TiLHO announced some important discoveries 

 in the Sahara in a paper read before the Royal Geo- 

 graphical Society on January 19. The Tibesti high- 

 lands prove to be an enormous triangular massif 

 twice the area of Switzerland, with summits more 

 than 10,000 ft. in height. Emi Kussi, the culminating 

 point of the region, is the largest of a series of 

 extinct volcanoes. This volcano has a well-formed 

 crater, which in the past was occupied by a lake, 

 but now has a thick deposit of sodium carbonate on 

 the floor. The population of Tibesti is considerable, 

 and is devoted to camel-rearing and brigandage. Col. 

 Tilho claims to have disproved the possibility of former 

 river connection between Lake Chad and the Nile. 

 His ex,plorations show an extension of the highlands 

 formerly known to occur between the southern borders 

 of Tripoli and Darfur. With regard to the economic 

 development of the Sudan and the Sahara, Col. Tilho 

 advocates an east-and-west transcontinental railway. 

 That this would facilitate the pilgrimage to Mecca is 

 an important consideration for great Mohammedan 

 Powers like Britain and France. 



Dr. G. F. Kunz, the well-known authority on the 

 subject of jewelry in all its aspects, contributes to 

 Mineral Industry (New York: McGraw-Hill Book 

 Co., Inc.; London: Hill Publishing Co., Ltd., 1919, 

 vol. xxyii., pp. 604-28) his customary chapter on the 

 production of precious stones for the previous year. 

 It may be remarked that this annual volume is 

 written from the point of view of the United States. 

 Rather more than two-thirds of this chapter is devoted 

 to diamond, pre-eminently the precious stone. The 

 jewelry trade is such a sensitive barometer of general 

 trade conditions that we are not surprised to read 

 that the incidence of heavy war expenses and tlie 

 increase in taxation had sensibly checked the import 

 of precious stones into the United States in the year 

 1918; the initial figures for 1919 show, however, that 

 the setback was only temporary. We note that in the 

 United States, just as in this country, successful attempts 

 appear to have been made to develop the diamond-cutting 

 industry. We are told that the output of gem material 

 in the Rangoon district of Burma for the year 1917, 

 which is the latest year dealt with, was of much 

 NO. 2623, VOL. 104] 



higher value than that of the previous year, although 

 the quantity produced was slightly less. The jade 

 output in North Burma, which is wholly exported to 

 China, where it is highly prized, remains as prosperous 

 as ever. The United States does not produce much 

 gem material, what there is being confined mainly to 

 ruby, sapphire, turquoise, quartz, and tourmaline, 

 although diamonds are being mined in Arkansas. 



In a paper on the factors controlling climate, which 

 appears in the December, 1919, issue of the Journal 

 of the Franklin Institute, Prof. W. J. Humphrevs, 

 of the United States Weather Bureau, discusses the 

 theories which have been propounded to account for 

 the existence in the past of "Ice ages," which, after 

 enduring for a time, were succeeded by long periods 

 during which the conditions were again normal. 

 Solar variation, eccentricity of the earth's orbit, and 

 carbon dioxide in the earth's atmosphere are shown 

 not to be capable of affording satisfactory explana- 

 tions, while the presence of volcanic dust in the atmo- 

 sphere for any considerable period is proved to be 

 capable of accounting for a fall of temperature of a 

 few degrees Centigrade. The finest dust from Kra- 

 katoa probably reached an altitude of 40 to 80 km., 

 and took nearly three years to fall through the iso- 

 thermal layer of the atmosphere to the level of the 

 upper clouds. If the coefficient of absorption of solar 

 radiation by the dust is greater than its coefficient for 

 terrestrial radiation, the value of the pyrheliometric 

 constant will be diminished. The author shows that 

 there is abundant evidence of this diminution after 

 every considerable volcanic eruption. 



At the meeting of the Illuminating Engineering 

 Society on January 27 a discussion on colour-matching 

 by natural and artificial light took place. Mr. L. C. 

 Martin, in opening the discussion, gave a summary 

 of existing methods of producing artificial daylight. 

 One of the most convenient devices has been the use 

 of a special tinted glass transmission screen used with 

 electric incandescent lamps to remove the excess of 

 red and yellow rays. With the gas-filled lamp the 

 efficiency of such units is considerably improved, 

 33 per cent, being claimed for a sunlight unit and 

 19 per cent, when light from the blue sky is imitated. 

 A communication from Mr. M. Luckiesh, read later 

 in the evening, showed how widely such units are 

 being used in the United States. ' Mr. Martin ex- 

 hibited the Sheringham daylight lamp, and explained 

 that the overall efficiency of the blue-sky unit was 

 not widely removed from that obtained with similar 

 units using blue transmission screens. On the other 

 hand, the diffusion of the light from the extensive 

 coloured reflector surface used with the Sheringham 

 lamp is considered a distinct advantage. Mr. Martin 

 also showed some very striking colour changes in 

 dyed fabrics seen successively under artificial day- 

 light and light from a tungsten lamp. Mr. Bawtree 

 exhibited a form of colorimeter for the analysis of] 

 colour, and Miss F. E. Baker, in showing the tinto-j 

 meter testing apparatus, also described some experi- 

 ments on a new form of daylight lamp. A com-, 

 munication from Prof. Gardner, of Bradford Technical] 

 College, was also read. The production of artificial! 

 daylight is exciting keen attention, and severall 



