April 21, 1910] 



NATURE 



231 



For smaller thicknesses the behaviour varied greatly with 

 the material, but the author hopes to explain the whole of 

 the phenomena obser\'ed b}' means" of the ionisation theor)'. 



The launch of H.M.S. Colossus was carried out success- 

 fully on Saturday, April 9. This vessel has been con- 

 structed by Scott's Shipbuilding and Engineering Com- 

 pany, of Greenock. That the work has been carried 

 out expeditiously will be evident from the fact that the 

 keel was laid less than nine months ago. The ship will 

 have a displacement of 20,250 tons, and has a length of 

 510 feet, beam 86 feet, and a designed speed of 21 knots. 

 Parsons turbines and Babcock boilers of 25,000 horse- 

 power will be fitted, and good progress has been made 

 with these also. The launching weight was 7500 tons, 

 and the vessel was completely afloat 58^ seconds after the 

 first movement, which occurred without the vessel hanging 

 on the ways for any appreciable time. 



An interesting article on the development of the hvdraulic 

 reaction turbine in .America, by H. Birchard Tavlor, 

 appears in the Engineering Magazine for March. 

 -American makers have advanced greatly since 1S90, and 

 have abandoned the methods of " trial and error " in 

 vogue prior to that date, methods which caused the 

 Niagara Falls Power Company to go abroad for the 

 designs of their first machines. To-day, .American 

 designers are in a position to design and construct 

 machinery to meet the most severe requirements, and have 

 to their credit the largest turbines in the world, among 

 which may be mentioned the four 13,000-horse-power 

 Francis turbines, now operating in the plant of the Toronto I 

 Power Company at Niagara Falls. The author of the 

 article has given special attention to erosion, and brings 

 forward evidence which indicates that trouble owing to ; 

 this cause may be eliminated by correct design. Thus a 

 bronze wheel under a head of 266 feet was so eroded at 

 the end of a few months that it was necessrTTy to replace 

 it. A new wheel, of slightly different design, but of pre- 

 cisely the same material, ran five years without showing 

 any signs of wear. Electrolysis and chemical action are 

 considered by Mr. Taylor, who believes that both can be i 

 eliminated by properly designing the wheel blades. ! 



The issues of Engineering for April 8 and 15 contain a 

 detailed account of some experiments upon the flow of 

 water over triangular notches, carried out by Mr. James 

 Barr at the James Watt Engineering Laboratories at 

 Glasgow Universit}-, under the supervision of Prof. Archi- 

 bald Barr. The late Prof. James Thomson first investi- 

 gated this form of notch in i860 and 1861 with rather 

 crude apparatus. It speaks well for his skill as an experi- 

 menter that the present series, with elaborate and finely 

 constructed apparatus, show no divergence from Thomson's 

 conclusions. Thomson's law, that the quantity flowing 

 is, in almost all cases, proportional to the 5 2 power of 

 the head, has be«n verified. Further investigation shows 

 that the prevention of the inward flow of the water at the 

 sides of the notch, whether caused by the narrowness of 

 the channel of approach or by the roughness of the up- 

 stream surface of the notch, produces an increase in the 

 quantity flowing over the notch. Various notches were 

 experimented upon, the value of the coefficient in 

 Thomson's formula for a narrow surface, right-angled 

 notch being found to var^- from 0-3104 at a head of 

 2 inches to 0-2995 ^^ ^ head of 10 inches. Thomson's 

 average value of 0-305 for heads from 2 to 7 inches must 

 have been very near the truth. The articles are well , 

 illustrated, and give full tables and curves of results. 

 NO. 21 12, VOL. 83] 



Messrs. Coxst.able asd Co. are publishing immediately 

 a little book of pocket size, being a " Guide to the 

 Preservation of Health in West Africa," by Mr. Henry 

 Strachan, principal medical oflicer in southern Nigeria. 

 They announce also the forthcoming publication of a 

 series of essays dealing with the consideration of the 

 introduction of an international language into science. 

 Such a language has been constructed by an international 

 commission, and the English edition of the essays in 

 which it is presented is by Prof. F. G. Donnan. 



Messrs. W. Wesley asd Sox, Essex Street, Strand, 

 London, W.C, have just issued a classified catalogue of 

 manuscripts, books, and pamphlets on astronomy, in- 

 cluding the libraries of the late Miss A. M. Gierke, Dr. 

 A. .A. Common, Mr. E. Crossley, and Captain W. Noble. 

 The catalogue includes the titles of about 3700 works, 

 arranged in alphabetical order, according to authors' 

 names, in groups relating to the various branches of 

 theoretical and practical astronomy and astronomical 

 physics. The classification renders it easj" to find the 

 works which Messrs. Wesley have available upon any 

 particular subject of astronomical study or research, and 

 all who are desirous of filling up gaps in their libraries 

 should see this catalogue. 



OUR ASTRONOMICAL COLUMN. 



Observations of Comets. — In No. 4402 of the Astro- 

 nomische yachrichten Dr. Wolf directs attention to a 

 peculiarity in the form of comet 1910a. Besides the main 

 and subsidiary tails. Dr. Wolf's photographs show a 

 conical faint mass of material extending from the base of 

 the coma towards the sun, quite different from anything 

 he has seen in previous comets, and having the appear- 

 ance of a miniature zodiacal light. The point of the cone 

 was in position-angle 215°, 180° from the direction of " • e 

 axis of the. tail, and was at a distance of 13' from the 

 nucleus. 



Comet 1909^ (Daniel) was photographed at Heidelberg 

 on February 28, and Dr. Wolf also publishes the latest- 

 determined position of comet 1909a, determined from a 

 photograph secured on August 19, 1909, when the comet 

 was fainter than the sixteenth magnitude. 



Observations published by Dr. Graff in the same journal 

 show that during January coniet I909e was a large 

 nebulous mass, 3' in diameter, with a nucleus of magni- 

 tude 12-5. 



Objecti\-e-prism Determinations of Radial \'elocities. 

 — An ingenious method of determining, approximately, the 

 approach or recession of faint stars is proposed by Prof. 

 Pickering in Circular 154 of the Har\ard College Observa- 

 tory. Various methods have been proposed before, but 

 have not proved remarkably successful. In one of these 

 it was proposed to introduce a standard artificial absorp- 

 tion band in the spectrum of each star, but the didymium 

 and hyponitric acid filter then employed produced bands 

 which were far too wide and hazy for precise measure- 

 ment. 



This difficulty has now been largely removed by Prof. 

 R. W. Wood, who has devised a filter giving an absorp- 

 tion band at X 4272 which is distinctly more definite than 

 the hydrogen lines in first-t\T)e stars. The filter is a 

 weak solution of neodymium chloride, and further experi- 

 ments are in progress to reduce the thickness of the 

 absorption band by the addition of lanthanum and phos- 

 phoric acid. Trial exposures have shown that for ninth- 

 magnitude first-type stars the probable error, at present, is 

 about 10 km., and for eighth-magnitude second-type stars 

 somewhat less ; a number of reproductions of the photo- 

 graphs obtained accompany the circular. 



Prof. Pickering also enumerates the available objective- 

 prism equipment at Harvard, and states that they are 

 ready to take such photographs as may be desired : further, 

 he invites cooperation from astronomers experienced ii» 

 radiai-velocitv work. 



