686 



NATURE 



[Fkbru/ry 20, 1913 



injuriously affecting casuarina trees in Madras, by 

 Mr. V. S. Iyer, forming Forest Bulletin No. 11. The 

 worst offender seems to be the caterpillar of the moth 

 Arbela tetraonis, but the fat grubs of a longicorn 

 beetle are likewise harmful. 



No. 10 of the serial just quoted is devoted to an 

 account, by Mr. R. S. Hole, of the great outbreak of 

 bark-bormg beetle-larva in the coniferous forests of 

 the Simla district between 1907 and 191 1. Five 

 species were involved in this very serious attack. 



From among several articles in vol. vii., part ii., 

 of the Records of the Indian Museum, attention may 

 be concentrated on one by Dr. N. .■\nnand.ile on the 

 Indian fresh-water soft tortoises, or mud-turtles of 

 the family Trionychida?. The author recognises 'one 

 ^PeciM and two subspecies which were not included 

 by Mr. Boulenger in the volume on reptiles in the 

 "Fauna of British India," namelv, Anderson's 

 Irionyx nigricans, from Chittagong, which has 

 hitherto been insufficicntlv described, and two local 

 races of the widely spread Emyda ^rauosa. Nor is 

 this alh for Dr. Annandale resuscitates Gray's genus 

 Dogania for Trionyx siibplana, on the ground that 

 m the upper shell of this species the entire series of 

 costal plates is separated bv mural bones, instead of 

 the last pair meeting in the middle line. 



_In Records of the Indian Museum, vol. vii., part 

 iii., Mr. J. R. Henderson describes a new tortoise 

 Jrom the Cochin district of southern India, under the 

 name of Geoemyda svlvatica, Geoemvda being used 

 as equivalent to Nicoria. 



Eri or end! silk, the product of the caterpillar of a 

 large Assamese moth, of which the technical name 

 does not appear to be mentioned, forms the subiect 

 of the first number of vol. iv. of the Entomological 

 Series of the Memoirs of the Department of Agri- 

 culture of India. According to the authors, Messrs. 

 H. Maxwell-Lefroy and C. C. Ghosh, this silk, which 

 Irom Its nature cannot be reeled, is spun and woven 

 m Assam into an exceedingly durable cloth, wh'ch 

 readily takes vegetable dves. ExDcriments have been 

 undertaken at Pusa with the view of ascertainimr 

 whether the cultivation cannot be extended to other 

 parts of India, with results that appear promising. 

 As the cocoons are not damaged bv the moths in 

 m.aking their exit, there is no necessitv for killing the 

 latter, which renders the silk accentable to sects like 

 the Jains, who object to taking life in any circum- 

 stances. . R L 



V^ 



MAGNETIC PROPERTIES OF ALLOYS. 

 rOL. VIII.. parts i and 2, of the Transactions of 



the Faraday Society contain a series of papers 

 which were read at a special meeting of the society 

 held for the general discussion of the magnetic pro- 

 perties of alloys. The papers naturally fall into two 

 gimips, viz. those dealing with ferrous' and with non- 

 ferrous alloys respectively. 



The iron-carbon and iron-silicon alloys form the 

 subject of an exhaustive paper by Dr. Gurnlich, which 

 is of considerable importance in connection with trans- 

 former working. He finds that the presence of large 

 arnounts of silicon result in the metal, even when 

 quickly cooled, exhibiting a pearlitic structure rather 

 than containing the injurious solid solution of carbon 

 in iron. With prolonged annealing even the pearlite 

 is decomposed into fcrritc and temper-carbon. A 

 silicon content of 3 to 4 per cent, is necessary for this 

 effect, so that the good macnetic properties of thin 

 sheet-metal containing less than this amount of silicon 

 must h.ave another origin. Figs, i and 2 show an 

 alloy with 4-5 per cent, silicon and 0^29 per cent, 

 carbon. Fig. i is with the metal in th'- untreated 



NO. 2260. VOL. go] 



condition, and Fig. 2 after annealing at 975° C. The 

 annealing has resulted in the pearlitic structure giving 

 place to enclosures of temper-carbon, and the coercive 

 force has been reduced from r26 to o'65 C.G.S. units. 

 A paper by Messrs. Colvert-Glauert and Hilpert, on 

 the magnetic properties of nickel steels, describes a 

 series of tests the results of which are at variance 

 with the view that the peculiar magnetic properties 

 of these alloys are due to the nickel retarding the 



FlG. I.— 4-5 per cent. >llicLiniion alloy (untreated). 



change from 7-iron to a-iron. They find all their 

 nickel-iron alloys when quenched at 1200° C. to be 

 strongly magnetic, and they have come to the con- 

 clusion that at that high temperature a strongly mag- 

 netic compound is formed which persists through all 

 subsequent thermal treatments. 



Prof. VVedekind's paper on the magnetic properties 

 of compounds in relation to their stoichiometric com- 

 position summarises very clearly the present state of 



Kit;. 2.— 4-5 percent. >illcon-irjn alloy (annealea). 



knowledge on this important subject. It is found that 

 simple compounds of ferromagnetic metals are 

 throughout essentially more feebly magnetic than are 

 the metals themselves, so far as they represent one 

 particular degree of valency. Simple compounds of 

 the latent-magnetic metals (manganese, chromium, 

 vanadium, and (?) titanium) are generally more 

 strongly magnetic than the metals, and some of the 

 compounds exhibit residual magnetism. The maxi- 



