43° 



NATURE 



[January 30, 1919 



menace to existing museums, alreach 

 hindered in their usefulness by lack of both space and 

 fumls. It seems to be generally agreed thai local 

 museums should confine their exhibits of objects bear- 

 ing on the war to such as are of strictly local interest. 

 Hut even if this course is lolloped, an appalling 

 amount of duplication in the objects displayed will 

 result, without serving any useful end whatever. 

 Everything of debatable value, or which serves no 

 real educational end, should be severely left alone. 



Referring to Mr. W. R. Nash's article on the 

 diminution of rainfall with elevation above ground in 

 "British Rainfall, 11)17," our reviewer remarked in 



Nature of January iti thai the results there set forth 

 "rather suggestive Foi aircraft." Mr. Carle 

 Salter, joint editor of "British Rainfall," writes to 

 say that the diminution of rainfall with elevation, 

 with which Mr. Nash deals, "represents, not a natural 

 phenomenon, hut a dele, i in instrumental capacity. 

 There may be real variations in the amount of rain 

 falling at' different elevations above the ground, hut, 

 except at very great heights, the amount of variation 

 is prohablv hilling in comparison with the large 

 falling-off observed at Greenwich, amounting to 35 per 

 cent, at 50 ft." The article was taken by our 

 reviewer at its face value, and it does not contain 

 the explanation now given of the differences observed. 



A special article is given in the lima of January Jo 

 on "Rainfall in 1918," contributed by Dr. H. R. Mill, 

 director of the British Rainfall Organisation. Detailed 

 rain measurements given show the total fall at 

 numerous stations from all parts of the British Isles; 

 the results, however, are only tentative, and form a 

 small part of the voluminous records from more than 

 5000 stations, which will eventually be given in 

 "British Rainfall, 1918." The average fall for thirty- 

 five years, 1875-1909, is also given, and the difference 

 of 1918 from the average as well as the 191S fall 

 as a percentage of the average. The instances of 

 excess are four times as great as those of deficiency. 

 In Wales the excess is 13 per cent, of the average, in 

 Ireland 11 per cent., in England N. 10 per cent., in 

 Scotland 6 per cent., and in England S. 5 per cent, 

 of the average fall. At present the rainfall of the 

 British Isles as a whole, it is said, is passing through 

 a series of alternately comparatively wet and dry years. 

 The driest part of the country with respect to the 

 average was in the north of England and the east of 

 Scotland, where in some places the deficiency was as 

 great as 18 per cent. The greatest excesses of rainfall 

 in 1918 occurred in the west, where the average itself 

 is always the greatest. A map of the British Isles is 

 given showing the relative distribution of the rainfall 

 for the year. Attention is directed to the outstanding 

 feature of the wet September in 1918, when England 

 and Wales had nearly two and a half times the average 

 fall. Rainfall totals for London are given for each 

 month of 1918 and for the year, and the falls are 

 compared with the average for fifty years. The total 

 for the year at Camden Square was 29-69 in., which 

 is 118 per cent, of the average. Rain fell on 195 days, 

 which is thirty-two days more than the normal. 



The paper on "Electrical Oscillations in Antennas 

 and Inductance Coils," by J. M. Miller, published by 

 the U.S. Bureau of Standards (No. 326), will be found 

 useful by mathematical electricians, as it helps to 

 clear up some of the difficult points in the ordinary 

 working theory. The methods adopted at present 

 for measuring the electri - onstants of an antenna 

 are on a verv dubious footing, and so we welcome 

 this paper. Most authors apply the theory of circuits 

 having uniformly distributed electrical characteristics, 

 such as telephone and transmission cables, to antennas. 

 NO. 257b, VOL. I02] 



We have nevei been able to follow the reason of this 

 practice, and so we welcome Mr. Miller's paper as a 

 serious and partly successful attempt to find a sounder 

 basis ,m which to build radio-telegraphic practice. 



The Council of British Ophthalmologists has issued 

 the reporl oi the committee appointed to determine 

 Standards of illumination of Snellen's test types when 

 used in testing the vision of candidates for the publii 

 services. The committee is of opinion that artificial 

 illumination rather than daylight should be used in 

 order thai there may be no doubt as io iis adequacy. 

 The minimum illumination should lie sufficient "to 

 ensure that the brightness of the lest card is nui 1. -^ 

 than thai of a w\\ card with an illuniinat ion of 3 foot- 

 candles, lb. card should have a small surface and 

 be .is uniformly illuminated as possible, should not 

 be backed by a contrasting background, or have 

 brighl objects or glaring lights near it. Tin- testing- 

 room should be moderately illuminated. Three 

 methods of providing the proper illumination by means 

 of gas, oil, .mil electric light respectively are described 

 in the report. 



Tnr: booklet on "Photomicrography" issued b) the 

 Wratten Division of Kodak having gone out of print, 

 it is replaced during the paper shortage by "Notes on 

 the Use of Wratten 'M' Filters." Although much 

 smaller than the other, the new issue includes all the 

 valuable tabulated matter, and, of course, the various 

 items are brought up to date. In the table of the 

 exposure factors for the "M" filters with Wratten 

 "M" plates, the factors for Nernst lamps are with- 

 drawn, and those for the recently introduced Pointo- 

 lite lamp are introduced. Some new colour filters are 

 disci ibid. One converts light from a metal filament 

 lamp into equivalent daylight, and is also advantage- 

 ously used with the Pointolite lamp and the smaller- 

 powered half-watt lamps. Another is of a neutral tint 

 transmitting only about 3 per cent, of the incident 

 light, and is useful for focussing with a powerful illu- 

 minant or lengthening exposure when using low 

 powers. Filters that may advantageously replace the 

 usual green glass are described, and the firm hopes 

 shortly to be able to supply a blue filter to transmit light 

 of a dominant wave-length of 470, especially for visual 

 use when the greatest resolving power is required. 



Mr. Walter Jamiesok, of the physics department, 

 Allan Glen's School, Glasgow, has sent us a little 

 instrument for which he suggests the name " Ixio- 

 scope "; it is a modification of the spinthariscope of 

 Sir William Crookes. The device consists in a roughly 

 spherical lens made by blowing a bulb on the end of a 

 glass tube and filling it with water. The upper half 

 is then varnished, and while still wet is dusted over 

 with powdered zinc blende containing a very small 

 quantity of radium; viewing ibis from the bottom 

 through the water, the scintillations due to the a par- 

 ticles .ire distorted into nebulous points and streaks, 

 and are in constant movement. The streaks of light 

 on the outer edge of the luminous field appear to be in 

 rapid rotation. Mr. Jamieson stales that "eight out 

 of ten people insist that the rotation is anti-clockwise." 

 The illusion is certainly striking at first, but a few 

 seconds' concentration leaves one very uncertain, not 

 only of ihe suggested direction, but also of any actual 

 rotarj appearance at all. The effect is probabl) die 

 to the distortions produced by the imperfect lens giving 

 rise to an apparent maximum of motion on the outer 

 edges ,,l the luminous disc; this suggests a spinning 

 wheel. A worked sphere of glass coated with lumin- 

 ous powder in the same ua\ shows the dancing scin- 

 tillations in a normal manner, and there is no sugges- 

 tion « hati ver of rotation. 



