220 



NATURE 



[April 14, 192 1 



be followed in the sea. It is practicable to 

 "rack" the rivers, permitting the ascent of the fish 

 only through a narrow gap. It is even possible to 

 count the fish that so pass during short sample times 

 that can be averaged. Then the ratio of fish ascending 

 to spawn to the run of fish four or five years later 

 (when the hatched fry return from the sea) can be 

 calculated. Comparisons over a number of years can 

 so be made and a maximum degree of exploitation per- 

 mitted. The method is, of course, much more com- 

 plex than is here indicated, but it is all highly practic- 

 able. To such statistical investigation would, of 

 course, be added a prolonged study of the spawning- 

 beds in the head-waters, even the artificial improve- 

 ment and control of the spawning and the elimination 

 of the natural enemies of the very young' fry. To 

 some extent such investigations have been carried out 

 — in spite, it is said, of the opposition of the Secretary 

 of Commerce, whose non-appreciation of the value of 

 scientific investigation was all that might have been 

 expected. 



Now, however, the commercial interests are 

 threatened and the administrative attitude is likelv to 

 change — with results of value not only to the industry, 

 but also to general biology. J. J. 



Recent Applications of Interference 

 Methods.* 



PROF. MICHELSON said that since the armistice 

 he had been interested in three questions : the 

 measurement of the earth tides, a re-determination 

 of the velocity of light, and the measurement of the 

 diameters of fixed stars. 



In the first of these problems the experiment reduced 

 itself to the measurement of the difference in the 

 movements of the free surfaces of water at the ex- 

 tremities of a long pipe submerged in the ground. 

 Preliminary work was carried out with microscopes, 

 but the final records were obtained from the move- 

 ments of interference fringes. Records were taken 

 at intervals of two hours on a kinematograph which 

 worked continuously for a year. The results obtained 

 were plotted, and found to agree very closely with 

 those calculated from theory. 



In the re-determination of the velocity of light the 

 arrangement ultimately to be employed was the same 

 as that previously used by Prof. Michelson, except 

 that a much longer distance — say, twenty-five miles — 

 was contemplated. This was to permit a larger 

 angular movement of the rotating mirror, which in 

 this case consisted of an octagon of glass rotating at 

 about 1000 revolutions per second. If the speed were 

 so adjusted that the octagon described 45° during 

 the time taken by light to pass to the distant mirror 

 and back, the returning beam would be undeviated. 

 This condition could be determined to a much higher 

 degree of precision than was possible for the angular 

 measurements involved in previous determinations. 

 The application of interference to this work lay in the 

 method of making the angles of the octagon very 

 accurately equal. 



The third problem, that of measuring the diameters 

 of the stars, was solved on lines which Prof. Michel- 

 son had applied many years ago to the measurement 

 of the separation of double stars. The methpd con- 

 sists in varying the separation of two slits in front 

 of ^ the object-glass of a large telescope until the 

 visibility of the parallel diffraction fringes seen in the 

 focal plane of the telescope is a minimum. No exist- 



1 Abstract of the Sixth Guthrie Lecture, delivered before the Physical 

 Soriety of London on March ii by Prof. A. A. Miche'son, of the 

 University of Chicaaro. 



NO. 2685, VOL. 107*] 



ing telescope is of large enough aperture for this 

 condition to be reached in the case of single stars; 

 but by attaching an arrangement of mirrors in front 

 of the large loo-in. telescope at Mount Wilson 

 Observatory, which in effect increased its aperture to 

 20 ft., it had been possible to obtain a result for the 

 star a Orionis, the fringes from which disappeared 

 when the slits were separated by about 10 ft. This 

 corresponded to an angular diameter of just under a 

 twentieth of a second. 



University and Educational Intelligence. 



Prof, G. Elliot Smith is delivering two lectures, 

 one at Groningen University on April 14 and the 

 other at the University of Utrecht on April 16, 

 entitled "Vision and Evolution." These lectures are 

 being given under the auspices of the Dutch Royal 

 Academy of Sciences, and form part of the scheme 

 for the exchange of lecturers between this country and 

 Holland which has been referred to recently in these 

 columns. 



The Summer School of Civics, organised by the 

 Civic Education League, is to be held this year at 

 Guildford (Surrey) on July 30-August 14. Courses on 

 economics, anthropology, social biology, maternity 

 and child welfare, sociology, civics, and social psycho- 

 logy will be among those offered ; while practical 

 training in the presentation of civics (through public 

 speaking, etc.) and in the regional approach to civics 

 will also be provided. Full particulars may be had 

 from the secretary, Miss Margaret Tatton, Leplay 

 House, 65 Belgrave Road, Westminster, S.W.i. 



The governing body of Emmanuel College, Cam- 

 bridge, is offering a research studentship of the annual 

 value of 150^., which will be tenable for two years 

 and renewable in exceptional circumstances for a third 

 year. The studentship is offered to a research student 

 commencing residence at the college in October next, 

 and applications should reach the Master of Emmanuel 

 not later than September 17. The award, which will 

 be made on the evidence submitted by the candidates, 

 should include two certificates of good character, an 

 account of their career with the names of professors 

 or teachers under whom they have studied, a state- 

 ment of the proposed line of research, and evidence of 

 ability to undertake that particular class of work. 



When the closing of the Finsbury Technical College 

 was announced by the City and Guilds Institute in 

 July last the many friends of the college began to 

 take steps to avert the threatened disaster. A defence 

 committee, consisting principally of old students, was 

 formed, and it -presented a petition to the governing 

 body signed by many workers in all branches of 

 science and bv others connected with industry and 

 with some of the City Companies who felt that all 

 possible steps should be taken to continue the college. 

 The professional institutes and learned societies pre- 

 sented a memorial signed by their presidents, and 

 other bodies, including the National Union of Scientific 

 Workers, took such other action as seemed likely to 

 help. The strong hope that, with the assistance of 

 the London County Council and the Board of Educa- 

 tion, the future of the college might be assured for 

 the next five years was recently expressed by the 

 governing body to the defence committee and the in- 

 stitutions concerned. The success of the negotiations 

 is now announced, and it may be hoped that the 

 "permanence of the college will in the meantime be 

 assured without its distinctive character being in any 

 way impaired. 



