January 13, 1921J 



NATURE 



641 



inent. The pamphlet is illustrated with eight excellent 

 plates showing reproductions of photomicrographs of 

 <liatoms, foraminifera, sections of anitnal aiwi plant 

 tissues, anthers and pollen, etc. 



Iv Ardxives of Radiology and Klcclrotherapy for 

 November last (No. 244) Mr. H. .\. Colwell continues 

 his sketch of the history of electrotherapy. An account 

 is given of the introduction and use of the galvano- 

 cautery, electrolysis, and influence machines, with 

 illustrations of the first apparatus employed. It is 

 interesting to see that an " electrical room " wa^ 

 started at Guy's Hospital in 1836, and \arii vi-: forms 

 of electrical treatment were investigattJ by .\ddison, 

 Golding-Bird, and Gull among others. 



The Tidal Investigations and Results of the Cana- 

 dian .\rctic Expedition, 1913-18, are issued as vol. x., 

 part C, of the report of that expedition. Dr. W. B. 

 Dawson notes that observations were made for vary- 

 ing lengths of time at ten stations on the south and 

 cast of the Beaufort Sea. The low temperatures and 

 the consequent hardening of the oil in the clockwork 

 of the registering tide-gauges presented a difficulty, 

 which, however, was largely overcome by installing 

 the instruments in snow-houses. The temperature of 

 snow-houses can be kept at 40" to 50° F. by the 

 use of lamps without the walls thawing. The range 

 of the tide on the open shores was usually less than 

 I ft., and seldom as much as ij ft. At the head of 

 .Vmundsen (iulf it occasionally exceeded 2 ft. This 

 •-mall range is too slight to have any direct effect on 

 navigation, but sufficient to move grounded ice. 

 From the few data available it appears that the tide 

 enters the Beaufort Sea from the north and moves 

 southward and westward. Dr. Dawson recommends 

 the establishment of some permanent tidal station 

 for reference, and suggests the suitability of Herschcl 

 Island, which is one of the few localities in the region 

 with a settled white population. 



The relation of surface visibility of the atmosphere 

 to .suspended impurity is dealt with in the Meteoro- 

 logical Magazine for December by Dr. J. S. Owens. 

 In commenting on the difficulty of dealing with the 

 whole subject of visibility experimentally, and 

 especially with reference to the visibility of lights, 

 allusion is made to the scattering of light by the 

 small suspended particles in the air. Allusion is also 

 made to the important part that the perception of 

 colour plays in visibility, and it is stated that the 

 sensitiveness of the eye for blue-greens is greater than 

 for reds when the light is fading. Mr. N. K. Johnson 

 contributes a communication on the visibility of pilot- 

 balloons. He gives the results of an attempt made 

 at Shoeburyness to determine which colour is most 

 suitable for pilot-balloons, and especially for long- 

 distance work. When the sun is shining on a balloon 

 its visibility depends on its reflective power; without 

 the sunshine you have to depend on the opacity of the 

 balloon. The results are summarised as follows : — 

 {1) Against a background of continuous dense white 

 cloud either red or blue shouki be used. (2) H the 

 »ky contains slight cirrus or haze red is the correct 

 colour to employ. (3) On occasions on which the sky 

 ia cloudless and of a deep blue colour a white balloon 

 .thotikl be selected. The magazine shows that the 

 NO. 2672, VOL. 106] 



total rainfall in November varied greatly in difterent 

 parts of the British Isles. The general amounts 

 were : — For England and Wales, 49 per cent, of the 

 average ; Scotland, 106 per cent. ; and Ireland, 

 no per cent. 



We have received from the firm of Messrs. Adam 

 Hilger, Ltd., pamphlets describing their most recent 

 spectrographs. Instruments with quartz prisms and 

 lenses can be supplied ready for photographs to be 

 taken to give the whole spectrum from 210/1/1 to 

 >ioo /ifi. In some cases an accurate scale of wave- 

 lengths is mounted internally so that a contact print 

 of the scale can be obtained on the same plate as the 

 photograph of the spectrum. Concave-grating spectro- 

 graphs with the mounting designed by Mr. A. Eagle 

 are recommended, as this form is found to possess 

 many advantages in comparison with the classical 

 Rowland mounting. The apparatus occupies very 

 little space and possesses great rigidity. For the 

 investigation of the Schumann and Lyman regions of 

 the spectrum, which may yield most important 

 theoretical results, the same type of mounting is used 

 in a vacuum spectl-Ograph. By the use of two slits 

 the whole spectrum from 210 nii to 50/uju may be 

 obtained with one setting of the grating. This is the 

 instrument which has been employed by Prof. 

 McLennan and his fellow-workers. Messrs. Hilger 

 also construct an X-ray spectrometer as designed for 

 Sir W. II. Bragg on the principle of Dershem. 



The problem of the high-frequency resistance and 

 inductance of parallel wires is one that has been 

 studied very carefully by many physicists, including 

 .Maxwell, Kelvin, Rayleigh, and Heaviside. The 

 problem, however, which they considered was the sym- 

 metrical case of a cylindrical conductor when the return 

 current was so far away that its magnetic effects on 

 the distribution of the current in the cylinder could be 

 neglected. A notable advance in the theory has 

 recently been made by Mr. Harvey L. Curtis in a 

 paper published by the Bureau of Standards, Washing- 

 ton (No. 374). Mr. Curtis has developed a new mathe. 

 matical method by means of which he easily obtains 

 the ordinary solutions applicable to a concentric main, 

 and, in addition, obtains .solutions for two parallel 

 cylindrical m.iins at given distances apart. His solu- 

 tions have been verified experimentally by the Bureau 

 of Standards. It was found, for instance, that when 

 an alternating current of 3000 frequency was sent 

 through a circuit consisting of two parallel wires 

 0-651 cm. in diameter and 0039 cm. apart the ratio 

 of the alternating-current resistance to the direct- 

 current resistance was 24. If the ordinary formulae 

 had been applied the ratio would have only been 

 about 1-5. Similarly, it is shown both by theory and 

 by the experimental results obtained that the irregular 

 distribution of the current over the cross-section of 

 the wire due to tlv- proximity of the high-frequency 

 return current very appreciably diminishes the co- 

 efficient of self-induction of x\v rlrcuit. 



Thk "Index Medi< u \ 1 I .- iiinl Record of the 

 Current Medical Literature of the World " (Washing- 

 ton : Carnegie Institution of Washington), which has 

 hitherto hccn .1 tiionthly piiblir.ition, will in future be 



