March 17, 1892J 



NATURE 



479 



perimentally. If means for finding one curve are available, any 

 other required curve ould probably be found by the same 

 apparatus ; hence there was no need for analysis. Prof. Perry 

 remarked that experiments could not be made on a machine 

 before the machine was built ; whereas the E.M.F. curve could 

 be predetermined from its design. By analysis, its current 

 curve-, when working under various conditions, could be found. 

 Prof. Ayrton, referring to the mnemonic character of the 

 modes of representation described by Dr. Thompson, suggested 

 that the symbols in the author's book should be more mnemonic. 

 He himself was in the habit of using large letters for currents 

 and small ones for resistances : A and a for the armature, S and 

 .r for series, and Z and z for the shunt, currents and resistances, 

 respectively, and er and ^' for the series and shunt turns. He 

 also found the following " electromotive force " rule very con- 

 venient. Draw three rectangular axes, OM, of, and OE, as 

 shown in Fig. 2. If, then, of represents the direction of the 



>M 



force (magnetic), OM that of the motion, then oe shows the 

 direction of the induced E.M.F. Dr. Thompson, in replying, 

 said he thought Mr. Blakesley had misunderstood what had been 

 said, for no ambiguity existed. In describing the windings of 

 armatures, difficulty arose from want of proper names for the 

 various elements, and in his forthcoming work suitable names 

 had been given. To Prof. Ayrton he pointed out that in his 

 book he (Dr. Thompson) had used mnemonic characters, for 

 >V, 7-„ and r,n represented the resistances of armature, shunt, and 

 series magnet coils respectively. The symbol I for current had 

 also been recommended for adoption by the Frankfort Com- 

 mittee. He objected to Greek letters except for specific quanti- 

 ties, such as angles, specific inductive capacities, refractive 

 indices, &c. He appreciated the simplicity of Prof. Ayrton's 

 E.M.F. rule, but thought it would be better to rotate oe and OF 

 through a right angle about o.\i, thus giving Fig. 3. — A paper on 



^M 



Fig. 3- 



the flexure of long pillars under their own weight, by Prof. M. 

 Fitzgerald, was read by Mr. Blakesley. The subject of upright 

 pillars fixed at the base and free at the top is treated mathe- 

 matically, the differential equation being integrated in two 

 series, involving ascending powers of the variable. Putting L 

 for the ratio of length to diameter, the results, when applied to 

 thin steel tubes and rods, for which Young's modulus is taken 

 as 12,000 tons per square inch, show that the limiting height (in 

 feet) of pillars which can stand without bending is given by 

 H = 15^! for tubes ; and H = TlJ^^^' for rods. If 



L = 100, the maximum height of a tube is 1500 feet, the 

 diameter being 15 feet. For wires, L may have larger values, 



NO. II 68, VOL. 45] 



and the limiting length of a No. 28 B.VV.A. steel wire, is about 

 j 10 feet. In the case of pillars whose neutral axes are con- 



strained to be vertical both at top and bottom, the results show 

 I that a definite ratio must exist between the bending moments 

 . producing the constraints. — A paper on choking coils, by Prof. 

 j Perry, F.R.S., and a description of the uses of Rice's choking 



coils for regulating the brilliancy of incandescent lamps, by Mr, 



Hammer, were postponed until next meeting. 



Linnean Society, March 3.— Prof. Stewart, President, in 

 the chair. — A letter was read from the Home Secretary, convey- 

 ing the thanks of Her Majesty the Queen for the address of 

 I condolence which had been forwarded on behalf of the Society 

 : on the death of H.R.H. the Duke of Clarence and Avondale. — 

 The President announced the presentation by Sir Joseph Hooker 

 I to the Society of two medallion portraits of Sir James Ross and 

 Dr. John Richardson, whose names are well known in connec- 

 tion with Arctic exploration. The medallions were executed in 

 i 1843 by the late Bernhard Smith. A vote of thanks to the 

 I donor was passed unanimously. — Mr. Clement Reid exhibited a 

 collection of fossil plants and seeds which he had found asso- 

 ciated with the bones of Rhinoceros and other mammals in the 

 I neighbourhood of Selsea, and West Wittering. By means of 

 I diagrams Mr. Reid showed the exact position of the bed, and 

 : described the condition in which the various specimens were 

 I deposited. — On behalf of Mr. W. E. Beck with, of Shrewsbury, 

 1 Mr. H. Seebohm exhibited a specimen of White's Thrush 

 ! {TurdKs varius) which had been shot near Shrewsbury on 

 I January 14 last. He pointed out that this species, which in- 

 habits Eastern Asia, belongs to the sub-genus Oreocincla, an 

 exclusively Eastern group of ground Thrushes, and is the only 

 one which is Palaearctic and migratory. It does not breed any- 

 where west of the Yenisei, and its occurrence in Europe is 

 accidental. Mr. Seebohm added that it had been met with 

 twice in France, four times in Italy, three times in Belgium, 

 once or twice in Austria and Prussia, once in Norway, thirteen 

 times in Heligoland (between 1827 and 1884), and about a 

 score of times in the British Islands, including three occurrences 

 in Ireland, and one in the extreme south of Scotland. — On 

 behalf of Mr. A. Craig Christie, the Secretary exhibited some 

 specimens, as was supposed, of Lycopodium complanatmu , col- 

 lected in Scotland, on which it was suggested that the plant 

 might be regarded as British. In the opinion, however, of 

 Mr. James Groves, who had carefully examined the specimens, 

 and other botanists present, they were referable to Z. alpinnm. 

 Mr. Groves pointed out the distinctive characters of both. Mr. 

 Carruthers was of opinion that Z. complanatuvi had been met 

 with in the south of England, but not within the last ten years. 

 Mr. E. M. Holmes was under the impression he had seen it 

 growing a few years ago near Stroud. — A paper was then read 

 by Mr. A. D. Michael, on variations in the internal anatomy, 

 and especially the genital organs, of the Gamasince, a typical 

 sub-family of the Acari. In this paper the author gave the 

 results of two years' research, including many hundreds of 

 dissections and serial sections, with lengthy observations of 

 the living creatures. The comparison of variable organs was 

 worked out in numerous species, showing great specific differ- 

 ences. Four of the species were found to be previously un- 

 described, and for these the names Hamogamastis horridus, 

 H. nidi, Lcelaps oribatoides, and Z. ligoniformis were proposed. 



Royal Microscopical Society, February 17. — Dr. R. 

 Braithwaite, President, in the chair. — Prof. F. Jeff"rey Bell 

 said that he had, in accordance with the resolution passed 

 at the last meeting, forwarded a copy of the message of con- 

 dolence from the Society to the Prince of Wales, to General Sir 

 Dighton Probyn, and he had received the following letter of 

 acknowledgment : — " Sandringham, Norfolk. — General Sir 

 Dighton Probyn, Comptroller and Treasurer of the Household, is 

 desired to convey to the members of the ' Royal Microscopical 

 Society' the heartfelt thanks of the Prince and Princess ot 

 Wales for the Society's kind resolution, expressing sympathy 

 for their Royal Highnesses in their deep affliction.— yizw^/a/-^ 25, 

 1891." — Mr. Watson exhibited and described a new vertical 

 camera for photomicrography designed upon the same lines as 

 that used by Dr. Van Heurck. — The President then read his 

 annual address, postponed from the last meeting under the 

 special circumstances then mentioned. The subject chosen was 

 the impregnation and modes of reproduction in Ferns and 

 Mosses ; diagrams in illustration were exhibited and explained, 

 and specimens were also shown under microscopes. — A cordial 



