218 TAKING OF PORTRAITS BY PHOTOGRAPHY. [MEMOIR XV. 



no more than was necessary. It is not requisite, when 

 colored glass is employed, to make use of a large sur- 

 face ; for if the camera operation be carried on until the 

 proof almost solarizes, no traces can be seen in the por- 

 trait of its edges and boundaries; but if the process is 

 stopped at an earlier interval, there will commonly be 

 found a stain, corresponding to the figure of the glass. 



The camera I have used, though much better ones 

 might be constructed, has for its objective two double 

 convex lenses, the united focus of which for parallel rays 

 is only eight inches ; they are four inches in diameter in 

 the clear, and are mounted in a tube, in front of which 

 the aperture is narrowed down to 3 inches, after the 

 manner of Daguerre's. 



The chair in which the sitter is placed has a staff at 

 its back, terminating in an iron ring, which supports the 

 head, so arranged as to have motion in directions to suit 

 any stature and any attitude. By simply resting the 

 back or side of the head against this ring, it may be kept 

 sufficiently still to allow the minutest marks on the face 

 to be copied. The hands should never rest upon the 

 chest, for the motion of respiration disturbs them so 

 much as to make them of a thick and clumsy appear- 

 ance, destroying also the representation of the veins on 

 the back, which, if they are held motionless, are copied 

 with surprising beauty. 



It has already been stated that certain pictorial advan- 

 tages attend an arrangement in which the light is thrown 

 upon the face at a small angle. This also allows us to 

 get rid entirely of the shadow on the background, or to 

 compose it more gracefully in the picture; for this it is 

 well that the chair should be brought forward from the 

 background from three to six feet. 



Those who undertake daguerreotype portraitures will 

 of course arrange the backgrounds of their pictures ac- 



