July 18, 1878] 



NATURE 



Z'^Z 



an axis in the direction of the ray, such as any of the above- 

 named substances. The axes of the quarter undulation plate 

 being taken as axes of reference, p being the angle between the 

 plane of polarisation and one of these axe.-, (T half the difference 

 of retardation at a given point between the part of the light 

 resolved in a plane through the axis of the body and the part 

 resolved perpendicular to that plane, <^ being the angle between 

 an axis of the | -undulation plate and the perpendicular on the 

 axis of the body from the given point (which perpendicular is 

 taken as the initial line in the equation to the elUpse defining 

 the light at such point) and r, 0, being the co-ordinates of this 

 ellipse, the writer finds the equation to the ellipse to be 



I -^ A cos fl + B sin 20 = r - 2 (i - (As + B^)] 



where A = — cos 2 p cos 2 (p 



and B = sin 2p sin 2a- + cos 2p cos 2a- sin 2<i>. 



From this equation diagrams have been drawn to exhibit the 

 condition of the light at every point for different positions of 

 the polariser. For the simple case of salicene or starch, in 

 which the difference of retardation is the same, or nearly so, for 

 all distances from the axis of the body, the diagram consists of 

 a ring of ellipses of various eccentricities and inclinations, each 

 ellipse showing the condition of the light along the radius on 

 which it lies. For the general case in which the difference of 

 retardation is a function of the distance from the axis of the 

 body the diagram consists of two series of curves, one series 

 being * ' isomorphal " curves or curves along which the eccen- 

 tricity of the ellipse is constant, and the other series being "iso- 

 clinal," or curves along which the inclination of the axis major 

 of the ellipse to the perpendicular in the axis of the body is 

 constant. The general equation to the isomorphal lines is 



A2 + B" = constant ; and to the isoclinal lines is - = constant. 



B 

 These two series of curves completely define the form and 

 position of the ellipse of polarisation at every point and render 

 it easy to determine what appearances will be presented on 

 passing the light through an analysing prism in any given 

 position. The results obtained were illustrated by some expe- 

 riment. — Prof. W. C. Unwin made a communication on the 

 flow from orifices at different temperatures. A paper recently 

 appeared in The Franklin Journal of Science, by Mr. Isherwood, 

 giving results of experiments on this subject, and according 

 to him the volume discharged from a given orifice is increased 

 by about 12 per cent, on raising the temperature from 60° to 

 212°. It is difficult to accept this result, because the friction is 

 known to diminish the discharge by an amount much less than 

 12 per cent., and no other cause than a decrease of friction can 

 be assigned to account for Mr. Isherwood's results. In the 

 author's experiments the increase of discharge at 190° above that 

 at 60° was only 4 per cent., with conoidal orifices in the form 

 of the vena contracta ; with thin edged orifices the variation of 

 discharge was still less. He is disposed to think that the 

 great increase of discharge in Mr. Isherwood's experiments 

 was due to diminution of friction in a rather small pipe leading 

 to the orifices, and would not occur with any other arrangement. 

 — Mr. Graham then read a paper on complementary colours. 

 He stated that the three primaries are green, red, and blue, and 

 not yellow, red, and blue ; that yellow is a binary compound of 

 green and red ; and that yellow and blue when mixed form 

 white. He remarked that after looking at a green disc the eye 

 evokes another colour, but this is not seen unless certain condi- 

 tions are fulfilled ; thus the undulations must be arrested by a 

 gray surface : this was proved by an experiment in which a 

 green disc carrying a concentric ring half white and half black 

 was caused to rotate, when a medium gray was produced and 

 this at once arrested and made visible pink the complement of 

 the green. Several "other complementaries were shown by the 

 same means. Mr. Graham next showed how the grays can be 

 formed by cancelling either reflected or transmitted rays of white 

 light. The first of these cases is illustrated by white paper 

 painted over with a wash of Indian ink, and the second by the well- 

 known Berlin tiles, in which light and shade are obtained by giving 

 varying thickness to the ware. He showed that this last effect may 

 be imitated by piling strips of paper to varying heights, and he has 

 succeeded in photographing geometrical figures so formed. Lastly 

 the author explained a method of arresting and showing the com- 

 plementaries more satisfactorily than he considers has hitherto 

 been done. Six thicknesses of white paper are gummed toge- 

 ther and cut into a ring, a ring of the same size and shape being 



also cut from a disc of coloured paper, and the white rin" is 

 let in to fill its place. On observing such a disc by white trans- 

 mitted light the complement is seen through the ring. — Prof. 

 S. P. Thompson exhibited a series of magnetic figures illus- 

 trating electro-dynamic relations. The lines of magnetic force 

 around a wire carrying a magnetic current can be shown by 

 passing a wire through a glass plate, strewing iron filings around, 

 and tapping the plate gently. The filings may be fixed in their 

 places, if the plate has previously been gummed and dried, by 

 softening the gum with steam. Such a prepared plate may be 

 used to project the figures of the magnetic curves in the lantern. 

 Two parallel like currents attract, their curves forming a fio-ure 

 illustrative of the action ; or they repel if travelling in opposite 

 directions, the repulsion also being evident from the form of 

 the curvca. It was shown by a series of such lantern-slides 

 that a very large number of electro-dynamic relations can be 

 illustrated by curves produced in this manner. Figures were 

 thrown upon the screen illusti-ating the law of oblique currents, 

 the attraction of a magnet into or its repulsion out of a circuit, 

 the deflection of a magnetic needle by a current, and the mutual 

 tendency of a current and magnetic pole to rotate. A very 

 curious figure was produced by a current running through a 

 magnet longitudinally. A transverse section of the lines of 

 force at a pole gave neither the radial lines of the magnet nor 

 the circular lines of the current, but a series of spirals. It was 

 argued that Faraday's conception of the lines of force tending to 

 shorten themselves supplied the means of interpreting the physical 

 effects indicated by the lines of force in the various figures. — 

 The Secretary read a paper by Mr. C. H. Hinton, on the co- 

 ordination of space. If a cubical space be divided into twenty- 

 seven numbered cubes, and each of these be again subdivided 

 in the same way, and so on, the position of any point within the 

 initial cube can be expressed by a reference to the numbers of 

 the several cubes in which it is placed, and the more this series 

 of numbers is extended, the more accurately is its position de- 

 fined ; and, further, if we consider an expression of the form 



rqpotim.lkjih where each letter stands for 



any number from I to 27, and if m, before the dot, indicates 

 the unit space, it will be evident that by such an expression the 

 position of any point in space can be indicated with any degree 

 of accuracy ; each letter representing a space twenty- seven times 

 as great as that which immediately succeeds it ; or, in place of 

 27, any other number offering special facilities for any given 

 purpose maybe employed. The author then gives some account 

 of the manner in which the system can be utilised for classifying 

 chemical phenomena and in arranging plants, &c. — An adapta- 

 tion of the telephone and microphone for communicating vibra- 

 tions to the phoneidoscope, by Mr. Tisley, was then shown. 

 The metal disc carrying the soap film is fixed just above the 

 telephone plate, and, this being in circuit with a microphone 

 and battery, any vibration imparted to the microphone at once 

 sets the soap film in action, the characteristic figures being at 

 once obtained. — Mr. A. Haddon exhibited a modified form of 

 microphone which he has arranged with a view to make the 

 same instrument available for receiving sounds of any given in- 

 tensity. Its main peculiarity consists in having a thin strip of 

 elastic attached to the middle of the pointed graphite. By 

 varying the tension of this elastic, the sensitiveness of the instru- 

 ment can be accurately regulated. — The meeting of the Society 

 was then adjourned to November. 



Chemical Society, June 20. — Dr. Gladstone, president, in 

 the chair. — The following papers were read : —Contributions to 

 the history of the naphthalene series, No. 2, ^ naphthaquinone, 

 by Dr. Stenhouse and Mr. Groves. By the action of nitric acid 

 sp. gr. 1 '2 on this substance, mononitroy-j8-naphthaquinone was 

 obtained in red crystals. By the action of dilute sulphuric acid 

 a dark-coloured compound was obtained, which, on reduction, 

 yielded white acicular crystals, and on oxidation orange- 

 coloured prisms. The new quinone has the formula C20H10O4 ; 

 the authors purpose to call it dinaphthyldiquinone. It is very 

 stable. — On pyrotritartaric and carbopyrotritaric acids, by Mr. 

 G. Harrow. By saponifying diacetosuccinic ether with dilute 

 sulphuric acid, the author succeeded in preparing these two acids ; 

 the author has obtained sodium and silver salts, and discusses 

 their constitution. — Laboratory notes, by Dr. Armstrong. — On 

 the action of alkaline hyprobromite on ammonium salts, urea, 

 and oxamide. Prof. W. Foster. The author gives a resumi oi 

 the present state of our knowledge as to the action of hypo- 

 bromite on ammonium salts and urea, with some results of his 



