April 26, 1906J 



NA TURE 



617 



We have received a reprint from the Numismatic 

 Chronicle of a paper, by Sir John Evans, K.C.B., de- 

 scribing the silver medal or map of Sir Francis Drake, 

 which commemorates the voyage round the world com- 

 pleted in 15S0. Three, or at most four, examples of this 

 modal are known, two of which are in the British Museum 

 and one in Sir John Evans's collection. Sir John Evans 

 agrees with Mr. Miller Christy that the silver map and 

 that which is attached to the work of Peter Martyr, " De 

 Orbe Novo " (Paris, 1587), are from the hand of the same 

 engraver, about whom it is only known that the initials 

 of his name were " F. G. " 



Two reports (Nos. 107 and 108) have bpen issued by the 

 British Fire Prevention Committee containing particulars 

 of experimental tests of the fire resistance of concrete 

 floors. The two floors were practically identical in design, 

 and were subjected to the same conditions. The results 

 of the tests were, however, very different according to the 

 concrete aggregate used. The one having Thames ballast 

 concrete -for the protection of its steel-work failed, whilst 

 the other, with clinker concrete and coke breeze protection 

 to the girders, remained intact. No independent fire tests 

 on such a scale with floor areas measuring 15 feet by 

 22 feet have been previously carried out. 



At the Institution of Civil Engineers an interesting paper 

 on the resistance of iron and steel to reversals of direct 

 stress was read by Dr. T. E. Stanton and Mr. L. Bairstow 

 on April 10. The results of their experiments, which were 

 carried out at the National Physical Laboratory, may be 

 summarised as follows : — The superiority, in resistance to 

 reversals of stress, of moderately high-carbon steels over 

 low-carbon steels and wrought irons, which was discovered 

 by Wohler to exist when the rate of reversals was 60 per 

 minute, still holds when this rate is increased to 800 per 

 minute, although, according to Reynolds and Smith's ex- 

 periments, this superiority no longer exists when the rate 

 of reversals is in the neighbourhood of 2000 per minute. 

 So far as comparisons can be made between the results 

 of the authors' experiments and those of Wohler and Sir 

 Benjamin Baker, there is no marked reduction in resist- 

 ance due to raising the rate of reversals to 800 per minute. 

 Experiments in which the ratio of tension to compression 

 varied from 14 to 072 indicated that between these limits 

 the value of the maximum range of stress was practically 

 independent of the actual values of the limiting stresses in 

 tension and compression. The resistance of the materials 

 in three typical cases of rapid reduction of area of the 

 specimens has been determined. The failure of iron speci- 

 mens due to the development of the slip-lines of Ewing 

 and Rosenhain into cracks has been determined for the 

 case of direct stress, and the failure of moderately high- 

 carbon steel, due to the development of cracks in the ferritic 

 areas of the structure, has also been established. 



Messrs. Archibald Constable and Co., Ltd., will 

 publish shortly a work on " Recent Advances in the 

 Physiology of Digestion," by Prof. E. H. Starling, F.R.S. 



Sir Martin Conway has written a history of Spits- 

 bergen which the Cambridge University Press will shortly 

 publish under the title of " No Man's Land." 



The London Stereoscopic and Photographic Company, 

 Ltd., has issued a new catalogue of photographic apparatus 

 intended primarily for the use of amateurs. The list is 

 attractively produced and conveniently arranged, and copies 

 may be obtained post-free on application. 

 NO. I9O4, VOL. 73] 



The Country Press, 19 Ball Street, Kensington, has 

 published a series of twelve picture post-cards of the leaves 

 of British trees and shrubs showing the exact venation in 

 each case. These cards are intended for the use of 

 children and others taking up nature-study ; but it is to 

 be hoped that teachers will prefer to direct the attention 

 of their pupils to the actual leaves of plants, and to 

 encourage the children to collect and study natural objects 

 themselves rather than pictorial representations of them, 

 however correct and artistic these may be. 



OUR ASTRONOMICAL COLUMN. 



Employment of Selenium Cells during Total Solar 

 Eclipse. — During the total eclipse of August last, the 

 observers at Tortosa made use of selenium cells for the 

 double purpose of determining the variation in sunlight 

 during the progress of the eclipse, and of ascertaining the 

 exact moments of the beginning and end of totality. 



As is generally known, the electrical conductivity of 

 selenium increases on exposure to sunlight, being especially 

 sensitive to the less refrangible end of the spectrum ; there- 

 fore, by placing the cell in series with a battery and a 

 delicate reflecting galvanometer, the amount of light fall- 

 ing on the selenium may be registered by registering the 

 movements of the galvanometer beam of light. 



Whilst the decrease of light, during an eclipse, is not 

 visible until the eclipse is well advanced, the galvanometer 

 needle at Tortosa was seen to move immediately after first 

 contact, and for nearly an hour showed a uniformly in- 

 creasing resistance. 



Assuming that the light during totality was of the same 

 quality as that obtaining at dawn, the results derived from 

 the observations show that its brightness was about equal 

 to that of the sky some thirty or forty-five minutes before 

 sunrise. 



The results obtained regarding the instants at which 

 totality began and ended were very satisfactory, and it is 

 suggested that, by placing similar equipments along the 

 line of totality during future eclipses, far better results 

 could be obtained than by the visual observations hitherto 

 depended upon (Astrophysical Journal, No. 2, vol. xxiii.). 



Catalogue of Pleiades Stars. — We have received from 

 Dr. R. S. Dugan, of the Princeton (N.J.) Observatory, a 

 copv of the inaugural dissertation presented by him for the 

 doctorate of the Heidelberg University. 



This publication contains the magnitudes and mean 

 places (for 1900-0) of 359 stars of the Pleiades group. In 

 addition to the catalogue. Dr. Dugan discusses the methods 

 employed in measuring the plates and reducing the data 

 thereby obtained. A chart of the group, on which the cata- 

 logue number of each star is shown, also accompanies the 

 dissertation. 



The Total Solar Eclipse of the Sun of January, 

 1907. — Among the numerous important papers communi- 

 cated to the meeting of the Astronomical and Astrophysical 

 Society of America, held at New York on December 28-30, 

 1905, there is one by Prof. David Todd which will prob- 

 ably be found to be of special interest to eclipse observers. 



Prof. Todd and Mr. Baker have computed the essential 

 data for ten possible stations, and have discussed the latter 

 and the means of getting to them. It appears that the 

 new railway across Russian territory will afford the 

 greatest facilities for reaching the Turkestan stations, 

 whilst observations will also be possible some 600 miles 

 north-west of Peking. The complete discussion is to be 

 published in the American Journal of Science [Science, 

 586, vol. xxiii., N.S.). 



Observations of Nebulje. — Since the year 1884 M. 

 Bigourdan, of the Paris Observatory, has been assiduously 

 employed in making a complete survey of nebulae. 



The results of this survey are to be published in five 

 volumes, of which two (iv. and v.), dealing with the 

 nebulae situated between 14I1. and 2411., have already 

 appeared. 



At the meeting of the Paris Academy of Sciences held 

 on March 19, M. Bigourdan presented the second part of 



