November 24, 192 1 J 



NATURE 



417 



From an altitude of 12,000 ft, it could be plainly seen 

 like a large empty irrigation canal, stretching away 1 

 for ten miles to the south until it was lost in the 

 dust haze. Indeed, so permanent are the dis- 

 location features in the desert regions that those 

 produced during the earthquake of 1857 are still 

 plainly visible. Mr. Willis thus concludes that the 

 aeroplane can be used with advantage as a means of 

 rapid geological reconnaissance in mapping large struc- 

 tural features. 



In an article on rudder pressures and Airship R38, 

 Engineering of November 11 it is pointed out that our 

 information as to the actual forces operating on a 

 ship when its rudder is in use is extremely limited 

 and indefinite. In light structures such as those of 

 airships it is therefore necessary to allow a more 

 generous factor of safety for the structural portions 

 which have to withstand these forces than for any 

 other portion of the structure the straining action of 

 which is more definitely known. It is p>ossible to 

 arrange the weights in an airship relative to the 

 buoyancy, so that the shearing forces and bending 

 moments operating on the structure as a whole may 

 be reduced to very small amounts. If, however, more 

 efficient control is required, and especially for move- 

 ments in the horizontal plane, larger forces on the 

 structure are involved, and the framing must of 

 necessity be stronger. It is from airshif>s that more 

 definite information as to the actual pressures on 

 rudders and other control surfaces can be obtained. 



since the actual pressure at various points can be 

 measured simultaneously without much difficulty. 

 Certain information on this point has already been 

 obtained, but has not yet been published. 



In the October issue of the Journal of the Chemical 

 Society Prof. J. N. Collie and Miss A. Reilly describe 

 the preparation of a new type of iodine compound. 

 This is obtained by the action of iodine on the barium 

 salt of diacetylacetone, and appears to contain iodine 

 in the ring. The formula attributed to the compound 

 is 



/\ 



CHs-CO-CH CH 



I I 

 HO-C CO 



\/ 

 CH 



On solution in water the iodine atom takes up the 

 elements of water and becomes quinquevalent. 



"The Legacy of Greece," edited by R. W. Living- 

 stone, which is shortly to be published by the Oxford 

 L'niversity Press, aims at giving an idea of the debt 

 of the world to Greece in various realms of the spirit 

 and intellect, and of what may still be learned from 

 her. The chapters most likely to appeal to readers of 

 Nature are Biology, by Prof. D'Arcy VV. Thompson, 

 Mathematics and Astronomy, by Sir Thomas Heath, 

 Medicine, by Dr. C. Singer, and Philosophy, by Prof. 

 J. Burnet. 



Our Astronomical Column. 



The Leonid Meteor Shower. — Mr. W. H. Denning 

 records that this display proved rather a feeble one 

 this year, and that very few of the meteors were seen. 

 Miss A. Grace Cook, of Stowmarket, watched the sky 

 for 3^ hours on the very clear, frosty morning of 

 November 11, and recognised six Leonids out of a 

 total number of twenty-five meteors seen. The radiant 

 point was in the usual position at 150+22°. Several 

 other observers maintained a vigilant watch on the 

 same date, but saw very few Leonids, though some 

 brilliant objects were recorded from the minor showers 

 of the period. There were radiant points in Taurus, 

 Auriga, Cancer, and Ursa Major. 



A New Suggestion to. Explain Geological 

 Climatic Changes. — Dr. Harlow Shapley contributes 

 a paper on this subject to the Journal of Geology, 

 vol. 29, No. 6. He has lately been observing the 

 seventy variable stars in or near the Orion nebula, 

 finding that thev belong to various spectral tvpes, 

 and that their light-curves are peculiar, showing no 

 regular periodicity, no extreme range of variation, and 

 little resemblance to other known light-curves. He sup- 

 poses that the changes are due to collision or friction 

 with the nebulosity. He then notes that the motion 

 of the sun is nearly straight away from the nebula, 

 and that, assuming the distance as 600 light-vears, the 

 sun was in its neighbourhood some 9,000,000 years 

 ago, in which case a variation of from 20 to 80 per 

 cent, of the total light and heat mav readilv have 

 taken place, more than enough to explain anv of the 

 changes ^ postulated by geologi5?ts. He makes the 

 further interesting notes that long-exposure spectro- 

 grams with the loo-in. reflector show the bright lines 

 NO. 2717, VOL. 108] 



of hydrogen, nebulium, helium, carbon, and nitrogen ; 

 and that they also show a faint continuous spectrum 

 in all parts of the nebula. This last fact makes the 

 difference from the spectra of the spiral nebulae one of 

 degree rather than of kind. 



Star Catalogues. — There have been extensive addi- 

 tions to pubUshed catalogues in recent months. 

 Greenwich catalogues cover the zone 24-32° N. decl., 

 and also the northern circumpolar region. The Astro- 

 nomer Royal contributed a paper to the meeting of 

 the R.A.S. on November 11, dealing with the proper 

 motions of the latter catalogue. He showed that 

 Drift I. was very strongly indicated, while Drift II. 

 could be traced, but was much less conspicuous, as 

 its apex was not far distant from the region of the 

 catalogue. The Cape Observatory has issued a cata- 

 logue of the stars in the Backlund-Hough list, which 

 was drawn up with the idea of covering the sky with 

 a fairly uniform network of stars the places of which 

 were to be well determined. Both Greenwich and 

 Cape observations indicate a surprisingly large cor- 

 rection to the equinox previousl\- employed ; this 

 correction has not yet been introduced into the Green- 

 wich catalogues, but the Cape catalogue adopts the 

 value —0048s.. deduced from observations of the sun. 

 Mercury, and Venus. The cause of the correction is 

 obscure ; some part of it may be due to the introduc- 

 tion of the travelling-wire method of observing transits. 



Washington Observatory has also published a cata- 

 logue of fundamental and zodiacal stars. It is par- 

 ticularly desirable to have the letter well observed, 

 since thev are employed to fix the positions of the 

 moon and planets. 



