2l6 



NA TURE 



[August i i, 1923 



of Prof. Steinach and others on the reversibility of 

 the sexes, the part played by the interstitial gland, 

 and the results of the transplantation of this organ. 



Among the books shortly to be published by the 

 Cambridge University Press we notice " Stories of 

 Scientific Discovery," by Mrs. D. B. Hammond, con- 

 sisting of short biographical sketches of Priestley, 



Lavoisier, Count Rumford, Herschel, Fabre, Faraday, 

 the Curies, Darwin, Wallace, and Pasteur ; vol. 4 of 

 the " Cambridge Medieval History," dealing with the 

 Eastern Roman Empire (717-1453), and " Founda- 

 tions of Agricultural Economics," by J. A. Venn ; 

 the aim of the latter is to give some account of 

 the origin and incidence of the numerous economic 

 problems which affect the agricultural community. 



Our Astronomical Column. 



An Oft-recurring Relativity Blunder. — Many 

 people have been temporarily misled by a fallacy in 

 considering the Einstein bending of rays of light. 

 They imagine that it ought to produce a sensible shift 

 in the position of the further component of a double 

 star, owing to its light passing close to the nearer 

 component, or similarly that the satellites of Jupiter 

 ought to undergo the shift at the time of occultation. 

 Another form of the fallacy is put forward by M. de 

 Saussure in Astr. Nachr. No. 5235, in an article 

 entitled " Influence de la deviation des rayons 

 lumineux sur la valeur du diamdtre du soleil." He 

 notes that the light from each limb of the sun would 

 be subject to the Einstein bending, but that since it 

 has only traversed half the gravitational field as com- 

 pared with a star behind the sun, the bending at each 

 limb is i*75'72. So far he is correct. His error comes 

 in when he asserts that the true diameter of the sun 

 is 175" less than that measured, equivalent to 1300 

 km. In fact we only see the full Einstein shift when 

 the distance from the eye to the place of bending is 

 small compared with the distance from the eye to the 

 object viewed. This is obviously the case for a star 

 near the sun, but not for the components of a double 

 star, for Jupiter's satellites or for the sun's limb. 



Since the Einstein bending is similar to refraction 

 we can easily see the fallacy by the following 

 example. Take a bowl 6 inches deep, and let a mark 

 on the bottom be just brought into view to an eye 

 placed horizontally behind the edge of the bowl, 

 when the latter is filled with water. Then the mark is 

 seen deflected through some 41*4° from its true place. 

 But if the eye be placed a mile away, still in the same 

 level, the deflection is no longer 41 "4° but only i9"5". 

 Similarly in the case of the sun's limb, the principal 

 bending takes place near the sun, and the enlargement 

 of the sun's diameter is not 175" but only about 

 o"oi" ; practically a negligible quantity. 



Spectroscopic Parall.\xes. — The Memoirs of the 

 R.A.S., vol. 62, contains a valuable paper by Mr. 

 W. B. Rimmer on the spectroscopic parallaxes of 

 500 stars, the types of which range from Fo to Mb. 

 The spectra were photographed at the Norman 

 Lockyer Observatory, Sidmouth, with the 12-inch 

 prisrnatic camera formerly belonging to Dr. F. 

 McClean ; a few of his spectrograms with the same 

 instrument are also discussed. The differences 

 of line-intensity were measured by the wedge 

 extinction method devised and recently described 

 by Dr. Lockyer. A special study was made of the 

 means for obtaining uniform results, and cases of 

 discordant readings were remeasured. A search 

 has been made for additional pairs of lines suitable 

 for the purpose, besides those used at Mt. Wilson ; 

 the enhanced titanium line at 4444 was successfully 

 adopted in conjunction with the cadmium line at 

 4455; the pair 4216, strontium, and 4250, iron, is 

 available for all types of spectra from F to M ; other 

 pairs have a limited range of applicability. 



In drawing curves connecting line-intensity with 

 absolute magnitude, use was made of all the trigono- 



NO. 2806, VOL. I 1 2] 



metrical parallaxes deduced by recent methods, equal 

 weight being given to all; 0005" (in Mt. Wilson 

 values 0002") was added, as the reduction to absolute 

 parallaxes. Some of the curves are reproduced in 

 the Memoir. The catalogue contains no dwarf stars 

 of types M or late K, as the spectra available from 

 which to draw curves are too few. 



All the 500 stars are in the Mt. Wilson spectroscopic 

 catalogue, and its results are printed for comparison, 

 the agreement being very satisfactory, esi)ecially in 

 view of the complete independence of method of 

 measurement. The parallax found for Arcturus is 

 0-145" 3^s compared with 0-158'' at Mt. Wilson, and 

 o-ioo" (trig.) at Yerkes ; its absolute magnitude is 

 i-o ; it therefore appears to be less remarkable for 

 size and speed than was formerly thought. The 

 brightest absolute magnitude in the catalogue is 

 e Geminorum, - 1-5; the faintest are seven stars of 

 mag. 6-0 and 6-i. 



Yerkes Observatory: Twenty -fifth Anni- 

 versary. — The Yerkes Observatory celebrated its 

 twenty-fifth anniversary last September ; the address 

 delivered on the occasion by the director. Prof. 

 Edwin B. Frost, has recently been printed. He 

 emphasises the paramount part played by Prof. G. E. 

 Hale in its establishment. The spectroheliograph 

 had recently been invented, and work with that 

 instrument has been throughout a principal feature. 

 The original spectrograph being inadequate for this 

 work, part of the funds bequeathed by Miss C. W. 

 Bruce were devoted to the spectroscope called after 

 her, and more than 8000 stellar spectrograms have 

 been obtained with it. These have already yielded 

 many important results, though the information 

 contained in them has not yet been fully in- 

 vestigated. 



The 60-inch mirror was offered to Yerkes Observa- 

 tory, but it was felt that it would have a \\ader field of 

 usefulness at ]\It. Wilson. 



Visual work with the 40-inch refractor included 

 Prof. Burnham's measures of double stars, and Prof. 

 Barnard's work on clusters, nebulae, comets, faint 

 satellites, etc. It was also found that the instrument 

 could be efficiently used for photography, by plac- 

 ing a yellow filter in front of the plate, which must 

 be isochromatic. Successful photographs have been 

 made of the moon, planets, nebulae, and clusters ; 

 6700 plates were taken for star-parallax. Allusion 

 is made to Barnard's splendid series of photographs of 

 comets, and the Milky W^ay ; the Atlas of the latter 

 is stated to be nearly ready for publication. 



The total solar eclipses of 1900 and 19 18 were 

 observed by members of the staff, and arrangements 

 are being made to observe that of next September in 

 California. It is pleasant to learn that the observing 

 conditions at Yerkes are probably the best that 

 could be obtained within 500 miles of Chicago ; the 

 40-inch instrument can be used for some 1700 hours 

 per year. 



The record of work is one of which the Observatory 

 may well be proud. 



