THE WOMBAT. 7g 



that a weak slide, if full of detail, intensified with the usual 

 mercury and soda sulphate formula will usually give a pleasing 

 colour, but a slightly over-developed slide is preferable ;.. 

 reduction to what is considered the proper density being 

 effected by means of a weak solution of hypo, to which has 

 been added two or three drops of a solution of the red 

 prusseate of potash ; this will also clear the slight fog which 

 the prolonged exposure and development causes, and a 

 sparkling transparency will generally result. 



If larger sizes are coated they will be found very useful for 

 line negatives for Photo-lithography, as they are very slow, 

 being about the speed of wet collodion, and give absolutely 

 clear glass, and with intensification, as much density as may 

 be desired. 



PROFESSOR RONTGENS X RAYS.* 



In the transactions of the Physical and Medical Society 

 of Wiirzburg, of Dec, 1895, Prof. Fr. C. Rontgenof that town, 

 has published a most interesting discovery of some new rays, 

 of which we will give an account, by reason of the extraordi- 

 nary importance which it is likely to attain in many respects.- 

 A high vacuum tube, similar to the well-known Geissler tubes, 

 and showing in a distinct manner the Cathodic rays when 

 excited by the discharge of a Ruhmkorff Coil, was for some- 

 purpose enveloped in a case of thin black cardboard, and Prof. 

 Rontgen observed at each discharge strong fluorescence on a 

 paper laying close by, which was soaked in Barium-Platin 

 Cyanide. The rays producing this phenomenon not only 

 penetrated the cardboard covering, but also all intervening 

 bodies, for instance a stout book of 1000 pages or some pine wood 

 boarding of several centimetres thickness, although to a vary- 

 ing degree. Whilst the wooden boards at two metres distance 

 from the vacuum tube were almost completely transparent to 

 the rays, an alum sheet of 1*5 mm. thickness already produced 

 a perceptible shadow on the paper, whilst a sheet of lead of 

 equal thickness proved to be entirely opaque. These newly 

 discovered rays are by no means identical with the Cathodic 



* " Helios," Feb., 1896. 



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