350 



NATURE 



[November io, 192 i 



mythical Keenan Land by getting a sounding of more 

 than 3000 metres on its site. It is of interest to note 

 that during his journey Mr. Storkersen and his com- 

 panions drifted on an ice-floe more than 450 miles 

 during six months, but were unable to discover any 

 definite current in the southern part of the Beaufort 

 Sea ; the direction of drift varied with the local 

 winds. This absence of definite current precludes the 

 feasibility of exploring the Beaufort Sea by an ice- 

 bound drifting ship. On the other hand, Mr. Stefans- 

 son hopes on his next expedition to explore it bv 

 means of small sledge-parties travelling over the sea- 

 ice and depending solely on seals for food. 



"Could the Drought of 1921 have been Fore- 

 casted? " is the subject of an article by Mr. C. E. P. 

 Brooks in the Meteorological Magazine for September. 

 The author suggests that while the abnormal weather 

 of the past spring and summer in Europe is fresh in 

 everyone's memory, it is an interesting exercise to 

 apply the principles of the Roseau Mondial, dealing 

 with the world's meteorology, and by constructing 

 charts of pressure and temf>erature deviations from 

 normal to attempt a prompt explanation. Charts 

 have been constructed for the months of December, 

 IQ20, to June, iq2i, comprising North America, the 

 Atlantic, Europe, India, and much of Africa. For 

 the period of the drought extending from February 

 to June anticyclonic conditions prevailed generallv over 

 Europe and North America. The pressure attained its 

 maximum near Valencia, where it was 62 mb. above 

 the normal, whilst at Spitsbergen the deficiency was 

 6-5 mb. Temperature was slightly below the normal 

 in the south, but much above the normal in the north. 

 Most of the district covered by the chart suffered from 

 drought. Especial mention is made of Exner's prin- 

 ciple, which asserts that low pressure over the Arctic 

 basin in winter is normally associated with high pres- 

 sure over the Atlantic west and south-west of Ireland 

 and with high temperature over the British Isles in 

 the same season. The author extends Exner's dis- 

 covery, arid is of opinion that some idea of the rain- 

 fall of the spring and early summer in the British 

 Isles may probably be obtained from a study of the 

 pressures and temperatures of the Arctic basin during 

 the preceding months. Low Arctic pressure is said to 

 cause low British rainfall, and high Arctic pressure 

 high British rainfall. 



Prof. H. H. Dixon, of Trinity College, Dublin, has 

 devised a handy method for the measurement of trans- 

 parent microscopical specimens situated on the stage 

 of any microscope possessing a reasonably good sub- 

 . stage condenser. A small transparent screen, divided 

 bv sets of thin black lines into small squares, is held 

 by a suitable adjustable folding stand so as to inter- 

 cept normally the light falling on the plane mirror 

 of the microscope. By a slight motion of the sub- 

 stage focussing adjustment the image (formed by the 

 substage condenser) of the lines on the screen is 

 brought into focus at the same time as the image 

 of the specimen seen in the microscope. Of course 

 the size of the intervals between the first images of 

 the lines has to be measured once and for all, either 

 arcuratelv bv means of a stage micrometer slide of 



NO. 2715, VOL. 108] 



the usual type, or approximately by means of some 

 object of known dimensions. In order to keep the 

 screen in a known position in successive measyre- 

 ments the top of it usually rests against the stage. 

 The makers claim that the regular sub-division of the 

 field by the images of the lines is of assistance in 

 making accurate drawings of microscopic objects. As 

 the result of tests, we can say that the arrangement 

 fulfils all that is claimed fur it. It is called the 

 "Ghost Micrometer," and is made by Mr. G. H. 

 Mason, 5 and 6 Dame Street, Dublin. 



The various theories of atomic structure current 

 at the present time agree in ascribing the spectrum 

 emitted by an atom to the electrons. If the electrons 

 emit radiation independently of each other the separa- 

 tion in a magnetic field of the components of a 

 spectral line should be proportional to the field, and 

 deviations from this law may be taken as indication 

 of some kind of coupling between the electrons. At 

 the suggestion of Prof. Nagaoka, of the University of 

 Tokvo, Mr. Y. Takahashi has measured the separa- 

 tions of a number of iron lines produced between 

 nickel steel electrodes by the spark of an induction 

 coil, in the field of an electromagnet capable of going 

 to 37,000 gauss. The separation was observed by a 

 Hilger echelon with a constant deviation spectroscope 

 behind it. For the nine strong violet lines seven were 

 found to give separations proportional to the field, 

 while two gave larger separations in stronger fields. 

 Of the weaker lines some give larger separations than 

 usual, which are not projjortional to the field. Both 

 facts point to the existence of some mutual influence 

 of the electrons on each other. 



During the war a considerable area of Northern 

 France and Belgium was entirely re-mapped, largely 

 from aeroplane photographs taken by a camera rigidly 

 fixed to the underside of the aeroplane. The methcwl 

 of using these photographs for map production is de- 

 scribed in Engineering for October 21, in an illus- 

 trated article by Mr. R. B. I'nwin. If the aeroplane 

 were slightly tilted when the photograph was taken 

 the result is a distorted view of the ground instead of 

 a true map. In mapping from aeroplane photo- 

 graphs it is therefore necessary to form a " frame- 

 work " on which to hang the photographs. The 

 framework consists of a number of points, the exact 

 position of which on the ground must be known, 

 and they must be such as can be identified on the 

 photographs. The original trigonometrical survey 

 points were used as primary points, and as these 

 were not sufficiently close to form a complete frame- 

 work, intermediate points were fixed. These inter- 

 mediate points were determined by the use of a plane 

 table behind our lines, or if behind the enemies' lines, 

 were deduced from the aeroplane photographs. At 

 least four points are necessary, which were set out 

 on a compilation diagram, and a tracing made and 

 attached to a board which could be tilted. Lines were 

 drawn on the negative joining the corresponding 

 stations, and an enlarging camera was employed to 

 project an image of the negative on the tracing. The 

 board was then tilted until the image of the lines 



