124 



NATURE 



[October i, 1914 



Besides the bulletin, the Review of Applied Ento- 

 mology continues to be issued by our Imperial Bureau. 

 The summaries of papers from all parts of the world 

 are of great value to workers, who will doubtless be 

 especially grateful to have the essence of much im- 

 portant Russian literature — otherwise unavailable — 

 brought within their reach. 



The twenty-first report of the Danish Biological 

 Station to the Board of Agriculture (Copenhagen, 

 1914) consists of an important memoir by Dr. C. J. G. 

 Petersen on the animal communities of the sea-bottom 

 and their importance for marine zoogeography. By 

 means of a new " bottom-sampler " the whole animal 

 population of a square metre of the area under inves- 

 tigation can be brought up in one haul, and the results 

 of numerous "valuations" of the sea-bottom at two 

 hundred stations in the North Sea and the Skagerrak 

 are set forth in statistical tables and photographs, 

 the latter reduced lo scale, giving a vivid impression 

 of the density of the population and the relative 

 abundance of its various members. By this method 

 of research, Dr. Petersen treats the marine fauna as 

 botanists of the ecological school treat the vegetation 

 of an area, and defines an " Echinocardium-Venus " 

 or a " Brissopsis-Turritella " community as character- 

 istic of certain regions. In the use of this method the 

 author believes that " the animals which are not 

 seasonal and which compose an important part of 

 the whole mass of the community owing to number or 

 weight, will presumably be best suited for characteris- 

 ing the community, and must also be considered as 

 giving a good idea of the outer conditions on wliich 

 the community is dependent." G. H. C. 



FATIGUE STRESSES. 



OINCE Wohler published in 1871 the results of his 

 •^ tests on the behaviour of steel under repeated 

 stresses a great deal of work has been done in this 

 direction. The experiments of Stanton, Eden, Rose, 

 and Cunningham are well known in this country. The 

 subject is a difficult one, and is complicated by the 

 lack of any satisfactory correlation between the tests. 

 Further, experiments on repeated and alternating 

 stresses take a long time to carry out. 



In his memorandum to the Manchester Steam 

 Users' Association, Mr. C. E. Stromeyer gives account 

 of some interesting experiments. Mr. Stromeyer has 

 found that all his tests could be harmonised by arrang- 

 ing for successive fatigue fractures on the same test 

 piece, I in. or i^ in. apart. From these tests an 

 empirical relationship was derived, and found to be 

 applicable not only to bending fatigue tests, but also 

 to push-and-pull, and to torsion fatigue tests. The 

 empirical formula is N = io^C*^(S^— FZ)*, in which 

 ±S„ is the nominal fatigue stresses to which a sample 

 is subjected, Fl is the fatigue limit of the material, C 

 is a constant for the given material, and N is the 

 number of repetitions of the stress S„, which the 

 material will stand before it fractures. The close 

 agreement of this formula with the test results is 

 demonstrated by diagrams given in the memorandum. 



An idea for determining the fatigue properties by 

 means of a single test suggested itself, and proved to 

 be so practical that a new machine has now been 

 constructed for the association with which fatigue 

 tests on the improved lines will shortly be undertaken, 

 both as regards push-and-pull stresses, bending 

 stresses, and torsion or shearing stresses. In prin- 

 ciple, the new test consists in determining the stress 

 at which the temperature of the test piece begins to 

 rise in consequence of internal friction. There is prac- 

 tically no internal friction in steel up to a certain 

 limit of stress, and hence no heat would be de- 



veloped in an alternating or repeated stress test within 

 this limit of stress. The test piece was surrounded 

 with a loose sleeve of thick india-rubber, and circulat- 

 ing water passed along the annular space between the 

 test piece and the rubber ; delicate thermometers were 

 used to measure the difference in temperature of the 

 inlet and outlet circulating water. At low stresses no 

 difference in temperature was noticed ; when a differ- 

 ence of about 001° C. was noticed the fatigue limit 

 was supposed to have been reached, but the fatigue 

 stresses were increased slightly in order to confirm 

 this indication. A considerable difference in tempera- 

 ture was now apparent, but would generally disappear 

 again if the alternating stresses were reduced below 

 the limit. These calorimetrically determined fatigue 

 limits were generally defined very clearly, and may be 

 depended upon as being nearly correct. 



Further, the calorimetric fatigue limits agree re- 

 markably well with the fatigue limits Fl found by 

 extrapolation of series of tests carried to the point of 

 fracture. Hence it is possible to shorten fatigue test- 

 ing from several weeks' or months' duration to one 

 or two hours. A single test piece is prepared — dupli- 

 cates, of course, are desirable — and submitted to 

 gradually increased fatigue stresses until the fatigue 

 limit Fl is found calorimetrically; then the stresses 

 are increased until a large quantity of heat is evolved, 

 and the alternations of stress are counted up to frac- 

 ture. These tests fix both Fl and also the coefficient 

 C. 



The method seems very promising, and may lead to 

 a simple workshop fatigue test of considerable prac- 

 tical value being adopted in many works where the 

 time occupied in alternating stress tests has hitherto 

 been a barrier. 



THE ROYAL SOCIETY OF NAPLES.'^ 



THE Atti and Rendiconti of the Royal Society of 

 Naples for the past year show what valuable 

 work is being done by this Society. The Atti (corres- 

 ponding to our Transactions) contain sixteen 

 memoirs, occupying more than five hundred quarto 

 pages. Papers of less importance are inserted in the 

 Rendiconti, which correspond to our Proceedings. 

 Attention should be directed to the very useful and 

 extensive bibliographies which accompany several of 

 the memoirs. 



While all the principal sciences are represented, it 

 is to the domain of pure mathematics that the more 

 important work belongs. Mr. G. Gallucci contributes 

 a valuable memoir on configurations (Atti, No. 4) ; 

 Mr. D. Montesano, others on the Cremonian groups 

 of numbers and the bilinear complexes of conies in 

 space (Nos. 7 and 8) ; Prof. E. Pascal describes inte- 

 graphs for differential equations (No. 16), and for 

 the graphical solution of integral equations; Mr. G. 

 Andreoli explains a method of determining superior 

 limits to the moduli of the complex roots of a given 

 algebraic equation. In the Atti (No. 10) 1VIr. R. 

 Giacomelli gives a biographical notice of Giuseppe 

 Ballo, a contemporary of Galileo. Among other 

 papers may be mentioned those of E. Guerrieri on 

 the light-curve of Mira Ceti, drawn from numerous 

 observations made during the years 1902-13, of 

 Dr. M. Fidele on the innervation of the reptilian and 

 batrachian heart (Atti, No. 2), and of F. Zambonini 

 on Vesuvian mineralogy (No. 12). 



The condition of Vesuvius since the eruption of 

 1906 is the subject of several interesting papers. 

 Prof. G. Mercalli, whose death last March deprived 



3 "Atti della Reale Accadrmia delle Sc'enze Fisiche e Matematiche 

 (Society Reale di Napoli)," vol. xv, 1914 ; Rendiconto, vols, xix, xx, June, 

 1913— June, 1914. 



NO. 2344, VOL. 94] 



