396 Progress of Invention, 



PROGRESS OF INVENTION. 



New Apparatus for Condensing Light. — An apparatus, which 

 has been found to render the light from a given source twelve times 

 as great as in ordinary circumstances, and which, when properly 

 constructed, is believed to be capable of still more important results, 

 has been lately invented at Lille. It consists of a hollow copper 

 vessel, in the form of an ellipsoid of revolution, and having its 

 interior surface silvered. At the extremity of the major axis, 

 which is farthest from the focus in which the source of the light is 

 placed, is an aperture of suitable size, that allows an exit to the 

 rays, after one half of them have been reflected once, and the re- 

 mainder three times. The extreme rays of the luminous cone thus 

 emitted forms an angle of 45°, but should it be desired to render 

 the rays parallel, they are to be thrown on a prismatic lens. To 

 afford a means of ascertaining the state of the light within the 

 instrument, apertures are formed in it which are fitted with 

 lenses that project images of the light, or a screen arranged 

 for the purpose, but do not sensibly affect the intensity of the 

 light. 



Engraving on Steel. — Photography has recently been applied 

 very ingeniously to this purpose. The steel plate, having been 

 covered with a mixture of gelatine and bichromate of potash, or 

 bitumen of Judea, is exposed under a negative obtained in the 

 camera ; after which the soluble portions of the coating are washed 

 off. The surface of the steel will then be found more or less un- 

 covered in the lights of the picture. The plate is next gilt in the 

 .usual way, by means of the electrotype process ; after which, the re- 

 mainder of the gelatinous coating is to be removed. It is then im- 

 mersed in dilute acid, which acts on the portions not protected by 

 the gilding, that is on those which are to represent the shades of 

 the picture ; the various grades being produced by the presence of a 

 greater or less number of particles of gold, which more or less pro- 

 tect the surface. When the plate is removed from the acid, and 

 washed, a number of copies may be printed trom it, and it will be 

 found to produce very excellent pictures. 



Tiie Drummond Light. — The opacity of the cylinders of lime 

 used with the Drummond light, is in many cases the source of con- 

 siderable inconvenience. This is obviated by very simple means, 

 which consists in the use of plates formed of magnesia and chloride 

 of magnesium. Being transparent, they permit the light td be seen 

 at both sides. One of them suffices for a small lamp ; for a large 

 one, such, for example, as is used in lighthouses, several are 

 arranged around a centre. 



The Glazing op Porcelain. — In ordinary cases a glazing is used 

 for porcelain, which has the convenience of being very easily fused, 

 but the disadvantage of being very readily attacked by acids, and 

 being extremely liable to become full of cracks. Moreover, the 

 presence of the lead, which is one of its constituents, is the source of 



