470 



NATURE 



[June 9, 192 1 



it has sunk back to some extent since its maximum 

 elevation in late Miocene times. There is thus be- 

 neath its surface a region of mass-defect, a " gravity- 

 synclinal." The sheets of detritus from the early chain 

 now dip towards their source, and the author once 

 more urges that the lakes penetrating the foothills on 

 either side are due to a reversal of the slope of primary 

 valley floors. The paper thus presented to English 

 readers is a clear and valuable addition to the litera- 

 ture of isostasy. 



In the Meteorological Magazine for April a summary 

 is given of the rainfall of San Domingo, dealing 

 chiefly with the eastern half of the island. Meteoro- 

 logical data from the Dominican Republic are said 

 to be extremely rare ; the rainfall records discussed 

 have been received by the Meteorological Office, and 

 are roughly summarised by Mr. C. E. P. Brooks. The 

 observations were forwarded by Mr. VV. A. Elders, 

 the general manager of the Samana and Santiago 

 Railway, who since 19 13 has had twelve rain-gauges 

 installed. A map is given showing the annual average 

 results for the twelve stations, which are situated 

 along the valley of the Yuna River and its tributaries. 

 Detailed monthly averages are given for Sanchez, on 

 the border of Samana Bay, at the eastern extremity 

 of the island, and for La Vega, situated near the 

 centre of the island, about sixty miles westward from 

 Sanchez. Results for Port au Prince, in the west of 

 the island, are added for comparison. Over the 

 eastern half of the island the heaviest rain occurs from 

 May to August, and there is a subsidiary maximum 

 in November. The driest months are from December 

 to March. There is a considerable range in the 

 annual rainfall. At Sanchez the average for the year 

 is 7109 in., ranging from 5600 in. in 1918 to 8152 in. 

 in 1913; whilst at La Vega the average annual fall 

 is 6758 in., ranging from 41-28 in. in 1920 to 10085 in. 

 in 1917. The prevailing wind is from the east, dis- 

 tinctly a trade wind, trending somewhat from the 

 south-east in the summer months and from the north- 

 east in the winter months. The country is moun- 

 tainous, but very fertile in the valleys. 



At the April meeting of the Optical Society Mr. F. 

 Twyman described an instrument for testing camera 

 lenses. The method depends on interference, and per- 

 mits of the measurement, in wave-lengths of the light 

 used, of the deviation from sphericity of the whole 

 of the wave-surface transmitted by a lens from a 

 point source behind it. This is secured by mounting 

 the lens under test so that it can be rotated about a 

 line at right angles to its axis passing through its 

 second principal point. The apparatus brings the 

 beam which has traversed the lens into interference 

 with one which has travelled a fixed distance, as in the 

 case of a Michelson interferometer. The isochromatic 

 lines of the interference pattern then correspond to 

 equal deviations from sphericity of the transmitted 

 wave surface. The instrument affords a most severe 

 test, and defects of lenses by first-class makers have 

 been found by its means. 



The report of the council presented at the annual 

 meeting of the Illuminating Engineering Society on 

 May 31 contains evidence of further useful work, new 

 NO. 2693, VOL. 107] 



joint committees in co-operation with various other 

 bodies having been formed to study special problems 

 arising from recent discussions. Amongst the subjects 

 thus dealt with are photometry, motor-headlights, and 

 the lighting of kinema studios. It is also remarked as 

 gratifying that international co-operation in connection 

 with illumination is being resumed. A session of the 

 International Illumination Commission, the first since 

 the outbreak of war, is being held in Paris in July, 

 and such questions as motor-headlights, " artificial 

 daylight," and regulations for industrial lighting will 

 be discussed. Following the formal business at the 

 annual meeting Mr. J. S. Dow read a paper on "The 

 Use of Artificial Light as an Aid to various Games 

 and Sports." An account of the lighting of various 

 covered tennis courts was given, and it was suggested 

 that even the artificial illumination of football and 

 cricket grounds and golf links, though admittedly pre- 

 senting considerable difficulties, might be accomplished 

 in the future. 



We have received from Messrs. C. Baker, High 

 Holborn, a descriptive pamphlet of a universal geo- 

 metric slide photomicrographic apparatus made by 

 them from the design of Mr. J. E. Barnard and 

 originally described by him in 191 1. The base is 

 designed on the girder principle to obtain rigidity, and 

 the portion carrying the microscope is constructed to 

 swing out so that the object may be searched. The 

 camera, a half-plate one, has a 3-ft. extension. The 

 upper surface of the base carries two parallel metal 

 rods, and the camera slides on these by two V-grooves 

 on one and a plane surface on the other, the latter 

 being intermediate in position between the V-grooves. 

 The principle of the geometric slide is thus obtained, 

 the apparatus being supported practically on three 

 points forming the apices of a triangle, while align- 

 ment is maintained by the V-groovcs. It may be 

 clamped down in any position, and by means of a 

 spindle running in bearings along the centre of the 

 casting, which actuates a pulley "belted " to the fine 

 adjustment with a thin cord, focussing may be carried 

 out at any position. All subsidiary apparatus, includ- 

 ing the illuminant, is similarly carried on geometric 

 slides. The price of the apparatus is 33?., or with 

 arc lamp and some subsidiary apparatus about 40L 



The April issue of the Whitehall Gazette contains 

 an interesting article on the fraudulent proceedings 

 that were practised to avoid service when conscription 

 was in force in this country. Some claimed exemp- 

 tion on the ground that they were suffering from 

 consumption, but declined to provide sputum there and 

 then, promising to send samples. The samples for- 

 warded did contain tubercle bacilli, but they were 

 dead, and the specimens were found to be artificial 

 concoctions. A good many forged passports were 

 produced by Russians who remained in this country. 

 In some cases a passport belonging to another would 

 have the written details bleached out by chemical 

 means and the desired name, etc., inserted. Some- 

 times the date of birth of the man's own passport 

 might be put back ten years. These forgeries were 

 detected by the change in reflecting power of the 

 surface of the paper caused by the removal of the size 



