9 + 



NA TURE 



[May 22, 1890 



With the exception of an enumeration of the flora of the little 

 island of Giannutri, off the coast of Tuscany, the number of the 

 Nuovo Gioi-nale Botanico Ilaliano for April is chiefly occupied 

 with a report of the meetings of the Italian Botanical Society, 

 held sometimes at Florence, sometimes at Rome. The papers 

 here reported are mostly of interest to Italian botanists : those of 

 more general importance being chiefly by Prof. Arcangeli, who 

 continues his researches on the interesting points of structure in 

 Ihe anatomy of Euiyaie, and other members of the water-lily 

 family. 



Memoirs of the St. Petersburg Society of Naturalists, Zoology 

 and Physiology, vol. xix. No. 2. — The article on the fauna of 

 the White Sea, by V. M. Shimkevitch, contains two separate 

 monographs. One of them deals with the Balanogiossus, and 

 is a detailed anatomical research into its structure, thus making 

 a most valuable addition to the work of Kovalevsky, Agassiz, 

 Metchnikoif, Spengel, Balfour, and Bateson. The author's con- 

 clusions are, that the Balanogiossus occupies an intermediate 

 position between the worms and the Chordata, It has originated 

 from a trochozoon which acquired some features in common with 

 worms, as well as some features distinctive of the Chordata. The 

 other monograph deals with the Enteropsis dubius, a new para- 

 sitic species closely akin to Aurivillius's Enteropsis sphinx 

 (Krustaceer hos arktiska Tunicater). The morphology and 

 embryology of this new Copepod are dealt with, and they are 

 followed by general remarks about the history of development 

 of parasitic Copepods. Both papers are well illustrated with 

 plates. — A paper by N. N. Polejaeff deals rather too 

 shortly with the following topics : on the filaments which 

 are found in the Hircinidce sponges ; on spermatogenesis 

 of the Forifera ; on the anatomy of Chalinida ; on the 

 Luffaria ; and on the new genus of Forifera, the Korotueivia 

 desiderata (with plates). — The appendix to the same volume 

 contains a detailed experimental inquiry, by A. Gendre, into the 

 causes of death in animals when the excretory functions of the 

 skin are artificially stopped. 



SOCIETIES AND ACADEMIES. 

 London. 

 Royal Society, May 8.— "On the Heating Effects of 

 Electric Currents. No. IV." By William Henry Preece, 

 F.R.S. 



The following table gives the fusing constants and fusing 

 temperatures for all the metals in general use when bare and 

 exposed in still air : — 



Copper 



Silver^ ... 



Aluminium 



German Silver 



Platinum , 



Platinoid 



Iron 



Tin 



Lead 



Alloy (lead 2 parts, tin i part) 

 The table means that if we take, 

 copper wire of i cm. diameter, a current of 2530 amperes will 

 raise it to 1054° C, and therefore fuse it ; and if we take any 

 conductor of copper of similar form, but of different diameter (</), 

 the fusing current (C) is 



C = 2530^1 

 The fusing current of any other material is obtained from the 

 equation 



C = ad'K 

 It seemed natural that these constants, marking such a 

 distinct and well-defined fiducial point, should also enable us 

 to obtain the currents that would raise the wire to any other 

 temperature. 



It is shown that if we determine C for any temperature, then, 

 since =:«C'', ©being the rise of temperature, the current C 

 producing any other temperature & is obtained by means of the 

 equation 



Now, for copper of i cm. diameter C = 2530 for 1054°. 

 Thus, if we want to find the current that will raise such a con- 

 ductor to 13°, we have 



C = 2530 . / ^^ = 281 amperes, 

 \' 1054 



if the surface be equivalent to the normal surface at white heal. 

 The coefficient which converts this normal surface emissivity 

 to that of the surface of ordinary wires at low temperatures by 

 taking the normal surface as unity, is as follows : — 



-y^ 



' G. Roux, V Electricien, December 



NO. 1073, VOL. 42] 



Surface 

 coefficient. 



Bright and polished copper 



Copper, dirty, oxidized, or blacked 



with shellac varnish o'6 



Copper, well coated with lamp-black i "o 



Thus, the current (C) producing 1054° {%) in a bare bright 

 copper cylinder of i cm. diameter is 05 X 2530 amperes, and 

 that which would produce a temperature of 10° C. is 



0-5 X 2530 



V 1054 



1 23 2 amperes. 



Thus, if we know the current producing any fixed temperature 

 in any cylindrical conductor, we can readily calculate the current 

 required for any other temperature. 



Physical Society, May 2.— Prof. W. E. Ayrton, President, 

 in the chair. — Mr. C. A. Carus- Wilson read a paper on the 

 distribution of flow in a strained elastic solid. The author 

 pointed out that when a bar is subjected to tensile stress the 

 elements of the bar are distorted by the resulting shearing 

 stresses which attain maxima in planes at 45° to the axis. If the 

 bar be supposed to be divided into elements such as P or Q (see 

 Fig. ), then if the shearing strains are equal in the two directions 



\^;7— --7 



dy^. 





y ./..I. 



-^ ^ 



\\>'\ 





parallel to the sides of the elements, the bottom points of the 

 strained elements will be directly below their top corners, 

 whereas if the strains be different in the two directions there 

 will be a displacement to one side or the other depending on 

 which side the greater strain occurs. Since each inclined section 

 is subject to the same total shearing force, the shearing strain 

 along any section such as EF may be taken as inversely propor- 

 tional to the length of the line EF, the bar being supposed of 

 uniform thickness. From these considerations it may be seen 

 that an element P will be subject to equal strains, for AB = CD, 

 hence the lower point of P will remain vertically below its upper 

 point. In this region, therefore, a horizontal straight line drawn 



