194 



NATURE 



[May 8, 1919 



geophysical institute, which is to deal with geodesy, 

 tidal phenomena, seismology, and allied matters, 

 has been approved, and a small committee is now 

 formulating a definite scheme. 



We notice the following among forthcoming books 

 of science: — "Air Navigation Notes and Examples," 

 Instructor-Capt. S. F. Card; " Tacheometer Tables," 

 Prof. H. Louis and G. W. Caunt; "The Principles 

 of Electrical Engineering and their Application," 

 Prof. G. Kapp, vol. ii.. Application (Edward Arnold); 

 "The Pituitary." Blair Bell; "The Heart: Past 

 and Present," Dr. E. Lea; "Injuries to the Head 

 and Neck," Dr. H. Lawson Whale (Bailliere, Tindall, 

 and Cox); "The North Riding of Yorkshire," Capt. 

 W. J. Weston; "Dumbartonshire," Dr. F. Mort, each 

 in the Cambridge County Geographies Series (Cam- 

 bridge University Press) ; " Economic Farm Build- 

 ings," E. P. Lawrence ; " The Universal Wages Cal- 

 culator," C. E. Lewton (The Library Press. Ltd.); 

 "Kraepelin's Psychiatry," vol. iii.. Dementia Praecox, 

 translated by Dr. R. Mary Barclay, edited bv Dr. 

 G. M. Robertson; "A Handbook of Surgery (Civil)." 

 C. R. Whittaker (Edinburgh: E. and S. Livingstone); 

 "The Principles of Child Physiology, Pure and 

 Applied," Dr. W. M. Feldman (Longmans and Co.). 



OUR ASTRONOMICAL COLUMN. 



Determination of Proper Motions. — In Circular 

 No. 43 of the Union Observatory, Johannesburg, Mr. 

 Innes publishes the result of an examination with the 

 blink microscope of pairs of plates of eighty astro- 

 graphic fields lent to him for the purpose by the 

 Astronomer Royal, the plates of each pair being 

 separated by an interval of nearly twenty years. The 

 fields cover the zone of the sky from declination 65° 

 to 67° N. through the whole twenty-four hours of 

 right ascension, and out of the whole number of 

 stars examined, estimated at 20,000, Mr. Innes has 

 found nearly four hundred which have a measurable 

 P.M., the large majority of which were previously un- 

 known. The largest motions are 290", 179", and 

 167" centennial on a Great circle. There are five 

 between 50" and 100", sixty-seven between 20" and 50", 

 and more than 300 less than 20" centennial. Two 

 hundred and fifty of the stars are in the Bonn Durch- 

 miisterung, and are, therefore, of all magnitudes down 

 to 95 or 10 visual, whilst the remainder are of 

 photographic magnitude 10 to 12, with a few fainter. 

 It will be realised that the motion of a star thus 

 determined is relative to the stars in a limited area 

 surrounding it, and not to the heavens as a whole. 

 The systematic character of the figures in the table 

 gives assurance that Mr. Innes 's work forms a useful 

 contribution to stellar statistics. 



The Blink Microscope. — -The fundamental prin- 

 ciple of this instrument is somewhat obscured by its 

 name. Having two similar photographs of the same 

 field of stars taken at some interval of years apart, 

 the obvious method of determining motion would be 

 to superpose these plates with identical images fitting 

 one on the other so far as possible, and then to search 

 for those images which do not fit. As actual super- 

 position is difficult, or impossible, for practical reasons, 

 a method only slightly less simple is to adjust the 

 plates side by side and measure the distances between 

 identical images with a measuring bar. This is the 

 principle of more than one type of instrument now 

 being used to determine proper motion. In the blink 

 microscope the images of the same star on the two 

 plates are seen alternately by rapidly closing and 

 opening shutters. Hence the name. Two images 

 which fit fall on the same spot of the retina, but those 



NO. 2584, VOL. 103] 



of a star which has motion do not, and give the sensa- 

 tion of a jump. The method of detection is therefore 

 simple, but it is clear that the measurement must be 

 made with discretion lest errors occur because of 

 imperfect adjustment or lack of exact similarity of 

 the plates. 



Calculation of . Occultations of Stars by the 

 Moon. — Mr. Arthur Snow publishes some tables for 

 this purpose in Popular Astronomy for February, 

 which should be of great use to those who do not 

 live near one of the stations (Greenwich, Washington, 

 etc.) for which special lists are available. He directs 

 attention to the fact that the region of visibility of 

 an occultation is a belt about half as wide as that 

 for a total solar eclipse, crossing the parallels of lati- 

 tude at a considerable angle, so that by no means all 

 the places that lie between the published latitude limits 

 enjoy a sight of the phenomenon. He gives full direc- 

 tions, which enable the limits of visibility to be laid 

 down on a map. 



X-RAYS AND BRITISH INDUSTRY. 



'X'HE war has furthered the progress and develop- 



■*■ ment of many industries, but probably no 

 department of science has received greater impetus 

 than that of radiology, using the word in the general 

 sense which it ought usefully to convey, and not in 

 that restricted sense which the medical world has 

 attached to it. The science and art of X-rays have 

 developed enormously during the war, and nothing but 

 good can result from the fact that the general medical 

 practitioner has had his eyes opened to the vista 

 which the X-ravs have revealed. He now realises, as 

 never before, that radiology is a new instrument of 

 attack for him — a veritable handmaiden, whether he 

 be physician or surgeon. The new diploma of radio- 

 logy which Cambridge and other universities are 

 about to establish is tacit recognition of the import- 

 ance of X-ravs in a medical curriculum. We wel- 

 come the suggestion that a chair of radiology should 

 be established at one of the universities in memory 

 of the late Sir James Mackenzie Davidson. 



But it is not our purpose at the moment to dwell 

 on the medical aspect of the rays. We are more 

 concerned with a development to which the Germans, 

 Americans, and ourselves have given considerable 

 attention during the past vear or more. We refer to 

 the examination of materials and built-up structures 

 bv X-ravs — a subject to which a joint meeting of the 

 Rontgen and Faradav Societies in the meeting-room 

 of the Royal Society devoted its attention on April 29. 



It is a very far cry from the days of Rontgen 's 

 famous discoverv some twenty-two years ago to the 

 present time. The technique has advanced amazingly, 

 but it can scarcely be said that apparatus and equip- 

 ment have made corresponding strides, although it 

 is, of course, not denied that considerable progress 

 has been made. We refer to this point later, but the 

 question is tied up with the attention the subject 

 has received at the" hands of the physicist and elec- 

 trical engineer. 



The meeting to which we have referred served 

 admlrablv to set out the development and present 

 limitations of the Industrial uses of X-rays, and those 

 of our readers who are Interested may be referred for 

 details of the meeting to the journals of the two 

 societies concerned. 



The great advantage of radiographv Is. of course, 

 the fact that we can spv out the Interior of an opaque 

 bodv without Injuring It In any way. Chief among 

 the materials which have been examined by the 

 X-rays Is steel, both carbon and alloy. Naturally, 

 the question of blow-holes and flaws In castings and 



