July 15, 1922J 



NA TURE 



89 



Lord Colwyn will open the research laboratories 

 of the Research Association of British Rubber and 

 Tyre .Manufacturers at 105-7 Lansdowne Road, 

 Croydon, Surrey, on Wednesday, July 26, at 3 p.m. 



The third report of the departmental Committee 

 on Lighting in Factories and Workshops, just issued, 

 deals mainly with the definition of " adequacy " of 

 lighting, which it has already been recommended 

 should be required by Statute and defined by Order 

 of the Secretary of State for different industrial 

 processes. The Committee considers that much 

 work still remains to be done before the regulation 

 of factory lighting can be established on a basis of 

 definite legal minima for illumination. Ample proof 

 is forthcoming of the relation between lighting and 

 production and safety. It is therefore suggested 

 that the chief industries should be invited to assume 

 partial responsibility by sharing in further investiga- 

 tions into the lighting requirements of work in these 

 industries. Meanwhile, as an indication of what is 

 desirable, the Committee furnishes an appendix in 

 which processes in the chief industries are classified 

 as " fine work," requiring 3 foot-candles, ' and " very 

 fine work," requiring 5 foot-candles. In other 

 appendices values demanded in American codes on 

 industrial lighting are given. It is gratifying to 

 observe that there has already been a substantial 

 improvement in industrial lighting since the Com- 



mittee commenced its labours, and there is no doubt 

 that the moderate course they recommend in regard 

 to legal minima will meet with general approval. 



Messrs. Gallenkamp and Co., referring to the 

 paragraph in Nature, July 1, p. 19, on the efforts 

 made by the Museums Association to get rectangular 

 glass jars manufactured in this country', remind us 

 that they are prepared to supply such jars. They 

 have been exhibiting samples at the Museums Associa- 

 tion Conference at Leicester this week ; we under- 

 stand that they were unable to make these jars when 

 approached by the Association. 



The attention of archaeologists may be directed 

 to a lecture delivered by Mr. G. B. Gordon at the 

 University Museum, Philadelphia, and published in 

 the Museum journal (vol. xii. No. 4), issued by that 

 institution, in which he describes the walls and other 

 antiquities of Constantinople. Mr. Gordon gives a 

 graphic sketch of the history of the city in relation to 

 the existing remains, and his lecture is illustrated by 

 an admirable series of photographs. 



A useful list (No. 432) of publications on agri- 

 culture and gardening, including some rare herbals, 

 has just been circulated by Mr. F. Edwards, 83 High 

 Street, Marylebone, W.i. It is obtainable free, upon 

 request, of the publisher. 



Skjellerup's Comet. — This comet was photo- 

 graphed by Mr. Davidson at Greenwich on June 21 

 and July 3. The results show that a slight lengthen- 

 ing of the period (previously given as 4-72 years) 

 is needed, and 5-1 vears is probably near the truth. 

 This is not unfavourable to the suggested identity 

 with Grigg's Comet 1902 II. Dividing the interval 

 by 4, 4-96 years is obtained as the mean period since 

 1902, and 5-1 years is quite within the limit of change 

 that might have been produced by Jupiter-perturba- 

 tions. These would have been considerable early 

 in 1905, and sensible in 1915. The new period is 

 much the same as that of Tempers Comet, for which 

 the value 5-16 years was found in 1920. This has 

 hitherto been reckoned the second shortest cometary 

 period. 



Profs. Crawford and Meyer of Berkeley Obser- 

 vatory, California, find the period 5-53 years for 

 Skjellerup's Comet, but this appears to be somewhat 

 too great, judging by recent observations. 



Periodical Comets. — An investigation has recently 

 been completed by Miss J. M. Young, instructor of 

 mathematics at the University of California, "on the 

 causes which have prevented certain periodical comets 

 being redetected on their predicted returns." 



She has brought a number of interesting facts 

 together, with regard to Barnard's Comet of 1884 

 and Denning's Comet of 1881, and concludes that 

 the most probable period for the former is 5-39 years, 

 and for the latter 8-84 years. Neither of the comets 

 alluded to have been redetected since the vears of 

 their discovery, but at certain returns the conditions 

 have been very unfavourable. Miss Young concludes 

 that periodic comets often escape observation owing 

 to the fact that they have not been searched for over 

 a sufficiently large extent of the heavens. 



NO. 2750, VOL. I IO] 



Our Astronomical Column. 



It is to be hoped that greater efforts will be made 

 to rediscover some of the numerous comets of short 

 period which have only been observed at one return. 

 Denning's Comet of 188 1 is due in 1925, when the 

 conditions may be favourable ; but there is consider- 

 able uncertainty as to the date of perihelion. 



Roche's Limit for Satellites. — It is not always 

 remembered that the limit assigned by Roche as 

 the minimum-distance of a satellite from its primary 

 (depending on the density of the latter, but of the 

 order of i\ times its radius) takes no account of the 

 force of cohesion in keeping the satellite particles 

 together. In the case of bodies of the size of the 

 earth or moon, the disruptive forces would be so 

 large that the force of cohesion might be neglected 

 compared with them ; but the case is different when 

 we consider little bodies like Phobos, the inner 

 satellite of Mars. Prof. George Darwin, in hi- well- 

 known work on the tides, etc., suggested that Phobos 

 was so near Roche's limit that future astronomers 

 might witness its disintegration. Dr. E. O. Fountain 

 gives some useful calculations on the subject in the 

 Journal of the British Astronomical Association for 

 May. He assumes as the tenacity of the material 

 forming Phobos about 300 lbs. per square inch, the 

 figure for brick and cement. On this basis he finds 

 that Phobos would still hold together even close to 

 the surface of Mars, while in its present situation a 

 satellite of 200 miles diameter could exist without 

 destruction. He also finds that bodies some 200 

 miles in diameter could exist without destruction 

 at the inner edge of Saturn's ring, so that the doctrine 

 of Roche's limit can scarcely be invoked to explain 

 the disintegration of the matter of the ring into such 

 tiny fragments as those which appear to constitute 

 I the ring particles. 



