Feb. I, 1877] 



NATURE 



307 



retarded more than the other in passing through the medium, or, 

 in other words, that they have different refractive indices. And 

 of course if a powerful iron magnet were transparent, we might 

 expect to find a much more powerful action of this kind upon 

 transmitted light. Iron, however, is not transparent, so that the 

 effect on transmitted light cannot be observed. But any effect 

 which this difference between the refractive indices can produce 

 upon reflected light may be made the subject of experiment, and 

 Mr. Fitzgerald has shown that the observation made by Mr. Ker 

 is an effect of this kind. 



To show this, Mr, Fitzgerald splits the incident plane polarised 

 light into its two equivalent beams of circularly polarised light. 

 These circularly polarised beams are one right-handed and the 

 other left-handed, and, before incidence, are equal in intensity to 

 one another. If, however, their indices of refraction in the 

 magnet are very different, as Faraday's and Verdet's experi- 

 ments lead us to suppose, their intensities after reflection will be 

 sensibly unequal, and their phases also will in general be 

 unequally affected. Hence their united effect after reflection is 

 to produce in general an elliptically-polarised beam, the major 

 axis of which is inclined to the plane of original polarisation, 

 thus producing that appearance of a slight change of the plane 

 of polarisation which was observed by Mr. Ker. 



Mr. Fitzgerald has repeated Mr. Ker's experiment, and ascer- 

 tained that the reflected light is, in fact, elliptically polarised, as 

 indicated by the theory. He has also found that when the 

 polished pole of the magnet is gilt the observed effect disappears. 

 This is a further confirmation of the theory, since gold is dia- 

 magnetic, and therefore too feeble to produce an appreciable 

 effect, if the effect is due to the cause which Mr. Fitzgerald has 

 pointed out. 



January 11, — " On some Phenomena connected with Vision," 

 by li. Thompson Lowne, F. R. C. S. , Arris and Gale Lecturer 

 at the Royal College of Surgeons, &c., communicated by Prof. 

 Stokes, 



The author arrives at the conclusion that the intensities of the 

 sensations produced by various illuminations of a white surface 

 vary as the square roots of the intensities of illumination, by 

 comparing the shadows, cast in Lambert's well-known experi- 

 ment, with ruled shades, as those of engravings and wood-cuts, 

 taking the amount of reserved white in the latter to indicate 

 directly the intensities of the sensations produced by them. He 

 considers the number of rods and cones stimulated on a given 

 area of the retina as the measure of sensation, and proportional 

 to the reserved white. 



He further finds, by a repetition of the experiment of MM, 

 Delbceuf and Plateau, that the grey ring seen on a rotating disc 

 with a black or white sector, disappears when the sector is suffi- 

 ciently narrow and the rotation sufficiently rapid, and that the 

 rate of rotation necessary to produce this result with the same 

 disc and sector varies as the square root of the intensity of the 

 illumination of the disc. 



Lastly, he proposes a modification of Fechner's formula, which 

 only requires a change of Fechner's convention that the liminal 

 increment of sensation is constant. The author proposes to con- 



sider that — r=^ oc A 6". The formula then becomes, in accord- 



/dx _ 



~^' = K^ x = S, which 



he regards as a physiological instead of a psychical one. 



Anthropological Institute, January 23, — Col. Lane Fox, 

 F,R.S., president, in the chair. — A new member was announced. 

 — Col. Fox then read his report to the Anthropometric Com- 

 mittee of the British Association on the Second Royal Surrey 

 Militia. The measurements, which comprised the profession, 

 race, origin, age, height, weight, chest measurement, colour of 

 hair and eyes, and strength of arm, &c., of 459 individuals 

 afforded some interesting lacts concerning what might be called 

 a fairly representative number of men from within a radius of 

 twenty miles round Guildford, It appeared that the colour of 

 the hair was in 391 cases brown or dark brown, and in only two 

 cases black, and m two cases red, one of the latter being Irish. 

 As to eyes, 311 were grey, light blue, or blue, 133 brown or 

 dark brown. Col, Fox proposed some modifications of the 

 existing tests of strength of arm and sight ; suggesting that in 

 the first the test should be the same as in drawing a bow, neither 

 hand being in any way supported, and the pull being from an 

 object not fixed. From a table of twenty comparative cases the 

 average of strength showed in the case of puUing from a fixed 



point, 165 "55 lbs., while the same men pulling with the one 

 hand against the other only 81 '95 lbs. From the general results 

 Col. Fox considered that the muscular strength, vital capacity, 

 &c., of our reserve and regular forces would show very favourably 

 in comparison with those of the ordinary population, and so dis- 

 pose of some of the frequent alarms given by the "man in the 

 street" as to the deterioration of our forces in physique. — Mr. 

 Street, President of the Philological Society, read a very inte- 

 resting paper on the development of language, and Mr. E. B, 

 Tylor and the President and others took part in the discussion. 

 — Papers by Mr. Knowles, of Ballycully, Ireland, on the clas- 

 sification of arrowheads, and on the "Portstewart find," were 

 also read, and numerous objects illustrating the papers were 

 exhibited. 



Physical Society, January 20. — Prof. G. C, Foster, pre- 

 sident, in the chair, — The following candidate was elected a 

 member ot the Society : Mr. A. G. Greenhill, M.A, — Dr. 

 Huggins exhibited an enlarged view of a photograph, half an 

 inch in length, of the spectrum of the star a Lyrse, which he 

 has recently taken in a manner similar to that in which the spec- 

 trum of Sirius has already been obtained. The first results were 

 very unsatisfactory, in consequence of the clockwork being in- 

 sufficient for maintaining the image of the star on the slit for a 

 length of time, Mr, Grubb has, however, devised a secondary 

 control apparatus, the employment of which renders it impos- 

 sible for the error to exceed one- tenth of a second. In the spec- 

 troscope employed the prism was of Iceland spar, and the lenses 

 of quartz. Dry plates were employed, and the necessary breadth 

 was secured by slightly changing the position of the image in- 

 stead of by the use of a cylindrical lens. Dr. Huggins has also 

 been engaged in taking a series of photographs of the moon, 

 and hopes to obtain some information in regard to the question 

 of a lunar atmosphere of small extent. In the spectnim of a 

 Lyras a line occurs corresponding with H^ in the solar spectrum, 

 and several more refrangible ones which he is at present unable 

 to explain. — Mr. Lockyer considered the results which Mr. 

 Huggins is obtaining to be of extreme importance, and he 

 pointed out how he hopes a large series of photographs of 

 stellar spectra will afford valuable information in regard 

 to the constitution of certain substances now supposed 

 to be elementary, such as calcium. Some time ago he com- 

 municated a paper to the Royal Society on the spectrum of 

 this metal, and he considers that it is not a simple substance, 

 but that the H lines are due to two elementary substances of 

 which it is composed, and this supposition is confirmed by the 

 fact that in the photographs exhibited by Dr. Huggins only one 

 of the H lines is present, that is, only one of the constituents of 

 the metal calcium is present in the star a Lyrse. — Mr, W, C. 

 Roberts read a paper on the artificial production of columnar 

 structure. He gave an account of the several theories which 

 have hitherto been given as accounting for this phenomenon 

 and that of cross-jointing, as observed in the Giant's Causeway, 

 and he dwelt specially on the views of Mr, R. Mallet and Prof. 

 James Thomson. He found as the result of experiment, that 

 when certain masses of clay and sand are heated to about 

 1300° C. they contract to about the same amount as a basalt 

 does in passing from the molten to the solid state, and that 

 beautiful columnar forms are produced. He had hoped, by 

 accumulating a number of specimens, to have been able to esta- 

 blish a relation between the strains at the point of rupture and 

 the dimensions of the hexagons, but in the small masses em- 

 ployed the strains were so numerous that it was impossible to 

 apportion their influences. He had, however, obtained a number 

 of specimens which possessed much interest. — Mr. Lecky re- 

 ferred to a very fine columnar cliff in the island of Bedness, in 

 Valencia Harbour, which he has examined in the hope of finding 

 cross-joints, but, although some breaks exist, there are none at 

 all comparable to those in the north of Ireland. — Prof. Guthrie 

 showed an arrangement he has recently devised, in the hope of 

 making the mercurial as sensitive as the water barometer. It 

 consists of an ordinary siphon barometer in which the two 

 vertical tubes are united by means of a long uniform horizontal 

 tube having a diameter considerably less than that of the main 

 tubes. The instrument is filled in the same manner as the ordi- 

 nary siphon barometer, except that a bubble of air or dilute acid 

 is left in the narrow tube. For a given rise of pressure the 

 absolute amount of mercury which passes from the shorter to the 

 longer tube depends upon their diameters, and as these are great in 

 comparison with the tube uniting them, the motion of the bubble 

 will be considerable in comparison with that of the summit of 



