A Manual Of Photography

42 HISTORY OY PHOTOGRAPHY. be obtec^ 1 souler" France, these designs may Great Britain Tt” promptly than in the uncertain clime of «^S" 16 !" ^°^ important that the time necessary is not exceeded, prolonged solarization has the effect of block graph. ’ seldom fail to produce a good photo- la re^ente^ apparatus inquired in this operation boar SA, is the lid of the box; a black with grooves to receive the plate ; c, cup containing a th^ ^ lamP; thermometer? G gL - ubh which to inspect the operation ; H, tablet as removed from the camera; i, stand for the spirit lamp. All the in- terior of this apparatus should be covered with hard black varnish. The board and the affixed plate being withdrawn from the camera, are placed at an angle of about 45° within this box—the tablet with the picture downwards, so that it may be seen through the glass G. The box being carefully closed, the spirit lamp is to be lighted and placed under the clip containing the mercury. The beat is to be applied until the thermometer, the bulb of which is covered with the mer- cury, indicates a temperature of 60° Centigrade, (140° Fahr.) The lamp is then withdrawn, and if the thermometer has . , risen rapidly, it will continue to rise without the aid of the lamp ; but the elevation ought not to be allowed to exceed 75° Cent. (167° Fahr.) After a few minutes, the image of nature impressed, but till now invisible, on the plate, begins to appear ; the operator assures himself of the progress of this development by examin- ing the picture through the glass, G, by a taper, taking care that the rays do not fall too strongly on the plate, and injure the nascent images. The operation is continued till the ther-