ADVANCEMENT OE SCIENCE. 1 1-3 



AN' IMPROVED STEREOSCOPE, BY M. A. CLAUDET. 



This is designed to remedy the illusion of curvature shewnlby plane surfaces 

 when examined by the refracting or semilenticular stereoscope, j This illusion 

 M. Claudet thinks arises from the fact that straight lines, viewed through a prism 

 or semilens; parallel to the base thereof, are bent with a concavity towards the 

 edge of the prism or lens ; and both the pictures in the stereoscope being bent in 

 the same manner, their coalescence produces a surface concave to the spectator. 

 To avoid this defect, only the central part of each lens is employed, and the axes 

 of the eyes are to be pointed in nearly parallel directions. In illustration of this 

 theory, M. Claudet mentioned a beautiful optical experiment. If holding a prism 

 in each hand, their refracting edges being vertical and turned towards each other, 

 the window of a room be looked at, at first, two windows are seen with their 

 vertical lines bent in opposite directions : by inclining gradually the optic axes of 

 the eyes, the two images can be made to coincide, and, in the single resulting win- 

 dow, the Intent curvature of the vertical lines ceases and is replaced by a curva- 

 ture from back to front, producing the illusion of a window concave to the spec- 

 tator. 



THE POLYHEDRON OF FORGES, BY MR. J. T. GRAVES. 



"If any number of forces act upon a point and be represented in magistude by 

 the areas of the faces of a polyhedron, their directions being normal to these 

 faces, they will keep the point at rest." 



This is an extension of the well known principle of the "Polygon of Forces." 

 It can also be applied to the composition of Couples, and Linear and Rotatory 

 velocities after the manner of Poinsot. 



THE LAW OF THE SQUARES — IS IT APPLICABLE OR NOT TO THE TRANSMISSION OF SIGNALS 

 IN SUBMARINE CIRCUITS?" BY MR. O. W. WHITEHOUSE. 



Before proceeding to the consideration of this subject, the author wished to 

 explain, with reference to his paper read on a previous day, that it was for the- 

 purpose of determining the force of either intermitting or alternating currents, 

 whose duration was not sufficient to admit of the needle assuming a position of rest, 

 that he proposed the use of the magneto-electrometer — an instrument rendering 

 available the force of magnetic attraction instead of the deflection of the needle — 

 as a means of measuring the amount of current circulating. This force was, he 

 said, until we approach the point of magnetic saturation of the iron, strictly propor- 

 tioned to the energy of the current under examination. The number of grains thus 

 lifted on the arm of the lever, the author proposes to call the practical " value" of 

 the current for telegraphic purposes. The most striking features of this instrument 

 are — 1st. The facility of determining the value of currents which do not admit of 

 being tried by the galvanometer ; — 2nd. The very great range which this instrument 

 has (viz., from unity up to half a million,) as well as the definiteness and accuracy 

 of the results, even the extremes of the register being strictly comparable with 

 each other ; — 3rd. Unlike the degrees upon the galvanometer, these grains of force 

 are units of real " value" and of practical utility, as was shown by a telegraphic 

 instrument in circuit being worked perfectly by a current of four grains. Refer- 

 ring to the proceedings of this Section last year, at Glasgow, the author quoted 

 Prof. W. Thomson's paper on this subject, where he stated " that a part of the 

 theory communicated by himself to the Royal Society last May, and published in 

 TOE. II; — H 



