108 SUMMARY OF CURRENT RESEARCHES RELATING TO 



crystallic forces, becoming amenable to the latter. He also shows that 

 every transparent medium containing metal spherules, so that the 

 average distance between two neighbouring spheres is considerably less 

 than a wave-length of light, has a perfectly definite colour by trans- 

 mitted light depending only on the optical constants of the metal of 

 which the spheres are made, on the refractive index of the substance in 

 which they are imbedded, and on the quantity of metal, but not on the 

 size or distance apart of the spheres. It results that the presence of 

 metal spheres accounts for the optical properties of gold ruby glass, and 

 that the irregularities in the effects of colour and polarisation, sometimes 

 exhibited by gold glasses, are due either to excessive distance between 

 adjacent gold particles or to excessive size of such particles — the latter, 

 however, involving the former. The author found that this regular 

 colour can be produced in a colourless metal glass containing the metal 

 in solution (which is the state in the manufacture of gold or copper 

 ruby glass before the second heating) by the /3-radiation from radium. 

 The author also investigates the optical property of media built up out 

 of metal spheres so that the volume of metal may have any value 

 between zero and unity, instead of remaining very small as in metal 

 glasses. He thus arrives at an explanation of the changes in colour of 

 gold and silver films observed by G. T. Beilby, and of potassium and 

 sodium films deposited on the insides of exhausted glass bulbs. 



Construction-Principle of an Optical Apparatus for obtaining 

 very Large Magnifications [The Diastoloscope].* — M. C. Chabrie 

 has investigated the question whether, instead of the ordinary mode of 

 obtaining an image geometrically like the object, it would not be more 

 advantageous to produce images, deformed but highly enlarged, and 

 then afterwards, by an inverse geometrical construction made on paper 

 to a suitably selected scale, reconstruct the objects in their true pro- 

 portions. His method depends upon the effect of viewing an object 

 (a disc) through a crystal in the shape of a right cone with an accurately 

 circular base. The cone-axis is arranged perpendicularly to the plane of 

 the object (fig. 27). The image projected on a screen is found to be an 

 annulus, whose centre is the point where the cone-axis meets the screen. 

 The point on the image immediately under the apex of the cone is re- 

 fracted into the outer circumference of the annulus, and other points in 

 the neighbourhood of that point are projected into the inner neighbour- 

 hood of that outer circumference. The magnification will be the ratio of 

 the image-circumference to the object-circumference. As the magnifica- 

 tion of the centre point of the object- becomes infinite, it will be readily 

 understood that points near it will be very highly enlarged. It will also 

 result that points on same concentric circumference of the image will 

 have equal magnification, and that, therefore, if a region of the object 

 between two points is to be examined, the object must be moved so as to 

 bring these points on to the same circumference in the image. The 

 object may of course be considered as composed of concentric, equi- 

 distant zones, whose common centre is the intersection of the cone-axis 



+ - Complee Rendus, exxxviii. (1904) pp. 265-8, 349-51, 5G0-3, 656 (14 figs.). 



