IP REPORT — 1853. 



of the velocity of propagation of such a movement would be proportional directly to 

 a coefficient depending on the rotative force, or polarity of the particles in a given 

 space, and inversely to a coefficient denoting the sum of the moments of inertia of 

 the luminiferous atoms in a given space, together with their loads of atmosphere, 

 round the axes of oscillation. The author shows that it is necessary to suppose that 

 the coefficient of polarity, for transverse axes of oscillation, is the same in all sub- 

 stances and for all directions ; and that the variations in the velocity of light depend 

 wholly on the variations of the moments of inertia of the luminiferous atoms, with 

 their loads, in different substances and round different axes. The coefficient of 

 polarity for longitudinal axes of oscillation must be supposed to be very great com- 

 pared with that for transverse axes. How powerful soever the polarity may be which 

 is here ascribed to the luminiferous atoms, it is a species of force which must neces- 

 sarily be wholly destitute of effect in producing resistance to compression or distor- 

 tion ; so that it is no longer necessary to suppose the luminiferous medium to have 

 the properties of an elastic solid. 



The author deduces from this hypothesis the known mathematical laws of the 

 wave-surface, of the intensity and phase of reflected and refracted light, and its 

 plane, circular, and elliptic polarization, and of all other phaenomena to which the 

 existing theory has been applied, the equations being identical in form. 



0?i the Composition and Figuring of the Specula of Reflecting Telescopes. 

 By J. D. SoLLiTT, Hull. 



The author of this paper was of opinion that all makers of reflecting telescopes 

 cast their metals too low in tin. He thinks they ought to be made in proportion to 

 the true atomic weights of the two metals, which would give 32 parts of copper to 

 17*4 of tin; and if this composition be found too difficult to work, it is easily 

 reduced without injuring the colour of the metal by the addition of one or two parts 

 of nickel. Such a composition he uses, and finds that the light reflected from it is 

 perfectly white; and when the telescope is made, b. front view one, very nearly equal 

 in quantity to an achromatic of the same aperture. He further observed that the 

 pores may be taken out of a composition containing them by the addition of. 

 metallic arsenic, he also repudiated the practice of fluxing the metal vath the salts of 

 potash or soda as being highly injurious. In polishing he uses extremely hard 

 pitch, so hard that no impression can be made upon it with the edge of a knife ; 

 and the polishing powder (either putty or colcothar) he grinds very fine on a slab, 

 and uses only a very small quantity, but works it down on the pitch for a very long 

 time, and in order to obtain a very fine polish only puts the powder on the tool once. 

 He prefers dividing the surface of the pitch by ten concentric circles, with six, eight, 

 or ten radii, the radii being made gradually wider towards the edges of the tool ; 

 and for the size of the tool, to produce a true parabolic figure, adopts the fol- 

 lowing formulae : Let D = the diameter of the metal, d =: the diameter of the tool, 

 and F = the focal length of the metal ; then, if worked with the metal below, 



d=:D— , or if the metal be above, d=T>-\- r^; in either case the metal will 



F-l-D F 



come oflF a true parabola, provided the pitch be of sufficient hardness and the powder 

 worked down a sufficiently long time to produce a high polish. 



Description of a Graphic Telescope. By Cornelius Varley. 



The author drew attention to the imperfections and difficulties experienced in 

 using the Camera Lucida, and then exhibited and described his instrument. The 

 stand of it united great portability with complete steadiness j and the instrument 

 itself, which had something of the appearance of a telescope, could be adjusted so 

 as to focus the image exactly at the spot where the pencil was to delineate it, and 

 the direct view of the point of the pencil easily caused to trace the picture to be 

 drawn. The object-end also of the instrument could be turned round so as to place 

 on the paper any portion of the landscape before the artist which he wished to deli- 

 neate ; or, if his object were to take the inside of a building, he could take the ceiling, 

 or roof, floor, or any portion of the sides, at pleasure. The Graphic telescope can 



