310 



NATURE 



[January 30, 1896 



passage of winged insects ? by Felix Plateau. The difficulty 

 experienced by insects in passing through a net with meshes three 

 or four times their own size has been variously explained. Some 

 attribute it to the resemblance to a spider's web, others to the 

 apparent multiplicity of obstacles. Experiments made with 

 nets of various shapes and materials show conclusively that the 

 peculiarity of insects in this respect is due to the construction of 

 their eyes, which are more adapted to the perception of motions 

 or changes in surrounding objects than to the perception of 

 form. When flying, insects are incapable of distinguishing a 

 net from a continuous translucid surface, and it is therefore only 

 very rarely that an insect will fly straight through it. It must 

 strike the meshes or alight on them, and will then pass through 

 as it would through any hole of the same size. 



SOCIETIES ANDACADEMIES. 

 London. 



Royal Society, January i6. — "The Rotation of an 

 Elastic Spheroid." By S. S. Hough, Isaac Newton Student in 

 the University of Cambridge. 



Recent researches on latitude-variation have brought to light 

 the phenomenon of a periodic motion of the earth's axis of 

 rotation in a period of 427 days. This period being in excess of 

 the theoretical period of 305 days hitherto accepted, Prof. 

 Newcomb has proposed to account for the extension by the 

 failure of the old theory to take into consideration the flexibility 

 of the solid parts of the earth. The author gives an analytical 

 investigation of the motion of a solid body when slightly 

 disturbed from a motion of simple rotation about a principal 

 axis, taking into account elastic distortions due to variations in 

 centrifugal force ; the results are found to agree in the main with 

 those obtained by Prof. Newcomb from geometrical considera- 

 tions. The analysis deals with the case of a homogeneous 

 spheroid of revolution, the ellipticity being such that the body 

 is free from strain when rotating uniformly. Such a spheroid, 

 if of the same size and mean density as the earth and rotating 

 with the same angular velocity, would oscillate in a period of 

 232 days if perfectly rigid ; it is shown that this period would be 

 extended to 335 days in virtue of elastic distortions if the 

 rigidity were equivalent to that of steel. In the case of the 

 earth the period would be still further prolonged in consequence 

 of variations in density, and the period which corresponds to the 

 above degree of rigidity is estimated at about 440 days ; whence 

 it is concluded that the observed period may be accounted for 

 by supposing that the earth is capable of elastic deformation, and 

 that its effective rigidity is slightly in excess of that of steel. 



Physical Society, January 24. —Captain Abney, President, 

 in the chair. — Mr. Campbell Swinton exhibited some photo- 

 graphs which he had taken by Prof. Rontgen's method. These 

 included several of metal objects inside wooden and cardboard 

 boxes, and a very clear and sharp photograph of the bones of 

 the hand. — Mr. E. Scott showed some geometrical instruments 

 invented by himself and Signor Monticolo. The instrument 

 designed by Signor Monticolo is intended for drawing arcs of 

 circles of such large radius that compasses cannot be employed. 

 It can be used to trace arcs of circles of which the radii vary 

 from 50 cm. to infinity. The second instrument exhibited was a 

 modified form of hatchet planimeter, which Mr. Scott has 

 devised with a view of avoiding some of the defects of the 

 ordinary form of instrument ; thus, to avoid the cutting of the 

 paper, which occurs when the knife-edge is sharp, and the side- 

 slip, which occurs when the knife-edge is blunt, the author uses 

 a wheel with a sharp edge. To avoid the inclination of the 

 instrument to one side, which may easily occur with the ordinary 

 form, a flat celluloid plate with a dot at the centre is used as the 

 ' ' tracing point," this plate being kept pressed flat on the surface 

 of the paper. A small wheel with a recording disc is attached, 

 and may be used to measure the distance between the first and 

 last position of the knife-edge. Mr. Scott also described a form 

 of planimeter which he had invented, and in which the I . cand 

 cylinder movement is used to perform the integra .on.- Mr. 

 C. V. Boys said that an instrument designed by Mr. Clarkson 

 had been exhibited before the Royal Society, which was capable 

 of drawing arcs of circles of large radius. This instrument 

 only drew an approximation to a circle, but the approximation 

 was so close that it nowhere was more than the thickness of a 

 thin ink line away from the truth. It would be interesting to 

 hear from the author whether Signor Monticolo's instrument 



NO. 1370, VOL. 53] 



drew a rigorously exact circle or not. The upright position of 

 the hatchet planimeter might be secured by using twO wheels in 

 place of one. The planimeter described was really a modified 

 form of one he (Mr. Boys) had described before the Society in 

 1881. Mr. Blakesley gave a short geometrical proof showing 

 that the curve traced by Signor Monticolo's instrument 

 was rigorously an arc of a circle. Mr. Blakesley also drew 

 attention to the fact that the instrument in its present form 

 cannot be used to trace the arc on both sides of the 

 zero line.— Dr. C. V. Burton described an idea for an 

 instrument for drawing circular arcs, which had occurred to him, 

 depending on the use of two wheels of different radii connected 

 by an axle carrying a tracing-point. In the absence of the 

 author, a paper by Prof. J. D. Everett on resultant tones was 

 read by Dr. Burton. The author, after giving a short summary 

 of the Ilelmholtz theory of the production of resultant tones, 

 goes on to discuss his objections to this theory, and to elaborate 

 a theory of his own. This theory depends on the consideration 

 that, if you analyse into a Fourier series a periodic curve which is 

 compounded of two simple harmonic motions of frequencies 

 n and m, then only two terms are obtained. If, however, some 

 error has been originally made in adding the two simple 

 harmonic motions together, this error being repeated for each 

 wave, then in addition to the two terms of frequency n and ut 

 there will be obtained, when the curve is analysed, a term of 

 frequency/, where/ is the greatest common measure of n and 

 m. This term of frequency / the author calls the common 

 fundamental of the tones n and m. The "error" in the pro- 

 duction of the compound curve the author supposes to be 

 produced during the transmission of the sound by the ossicles of 

 the ear. In support of his theory the author finds, that in the 

 violin where the sound-post, like the ossicles of the ear, transmits 

 the vibrations from one portion of the instrument to another, it is 

 easy by sounding two strings in conjunction to obtain combination 

 tones which agree in frequency with those required by this theory. 

 Thus, when the major sixth (3 : 5), the major second (8 19), or 

 the minor seventh (5:9) are sounded, the fundamental (i) is 

 clearly heard and also felt by the hand holding the instrument. 

 The author has also succeeded in picking out and strengthen- 

 ing this resultant tone by holding a Helmholtz resonator 

 in contact with the body of the violin. — Dr. C. V. Burton, 

 after explaining several portions of Prof. Everett's paper, said 

 that he (Dr. Burton) considered that the author^s view in many 

 ways seemed to fit in with the observed facts better than the 

 accepted theory, but still did not appear itself quite free from 

 objection. Prof. Everett supposes that the first term in a 

 Fourier series is always the most important, and although in 

 most cases which occur in practice this may be so, it hardly 

 seems legitimate to take this as a characteristic of a Fourier 

 series. — The thanks of the Society having been given to Prof. 

 Everett and Dr. Burton, the meeting adjourned to February 14. 

 Chemical Society, December 19, 1895.— Mr. A. G. Vernon 

 Harcourt, President, in the chair. — The following papers were 

 read : The liquefaction of air and research at low tem- 

 peratures, by J. De war.— Researches on tertiary benzenoid 

 amines, (i) Derivatives of dimethylaniline, by Miss C. de B. 

 Evans. On heating dimethylaniline with chlorosulphonic 

 acid only the para-sulphonic acid is formed ; fuming sul- 

 phuric acid must be used in order to obtain the meta-sulphonic 

 acid. The bromination and nitration products of these sulphonic 

 acids are described. ^ — Experiments on the formation of the so- 

 called ammonium amalgam, by J. Proude and W. H. Wood. 

 Solutions of phenols in aqueous ammonia contain ammonium 

 salts because they give ammonium amalgam on addition of 

 sodium amalgam ; no mercurial froth is obtained from ammo- 

 niacal aqueous solutions of several inorganic salts, so that these 

 contain no ammonium salts. Ammonium salts, when fused or 

 dissolved in anhydrous solvents, cause no swelling of the sodium 

 amalgam ; the presence of water seems essential to the forma- 

 tion of ammonium amalgam. — The molecular volumes of 

 organic substances in solution, by W. W. J. Nicol. The atomic 

 volumes of the various elements may be accurately determined 

 from the molecular volumes of organic substances in solution ; 

 the constants thus obtained differ somewhat for different sol- 

 vents. — 2 : I i3-naphthylaminesulphonic acid and the corre- 

 sponding chloronaphthalenesulphonic acid, by H. E. Armstrong 

 and W. P. Wynne. The 2 : i /3-naphthylaminesulphonic acid is 

 converted, by the Sandmeyer method, into 2 : i-j8-chloro- 

 naphthalenesulphonic acid of which a number of derivatives are 



described 



4'-8-naphthylaminedisulphonic acid is ob- 



