Photographical Section Proceedings. 1103 



scale may be pasted on the base or bottom frame of the camera and 

 a simple index attached to the sliding portion of the camera body. 

 Any one will understand the necessity of haying the surface of all 

 subsequent originals occupy the same relative position as those used 

 in establishing the various scales of the plate or paper of any original 

 are thicker or thinner, the truck of the plan-board must be moved 

 backward or forward, as the case may be, until the proper compensa- 

 tion is indicated by the index on the scale, F. 



For example, the operator has occasion to make a copy upon a 

 scale of four times tlie original, which, for convenience, he places 

 upon, nearly as may be, the center of his plan-board ; this center is 

 shown by the intersection of two right angle lines drawn through 

 the extreme length and breadth of the plan-board, as is often done on 

 the ground glass of the camera. Having placed his camera on the 

 truck, C, he proceeds to adjust the focus and size for his copy 

 upon the ground glass, by the necessary movements of the several 

 parts. After the negative is produced, and found to be of the 

 required size and satisfactory definition, he notes the position of the 

 indexes on the several scales, and afterward he is sure of correct 

 focus and size (for that scale) by referring to his note book or sheet 

 of scales and fulfilling the conditions there recorded. 



A list of scales for reduction, and another for enlargements may 

 tlius be made, with good subjects and light, which by frequent use 

 are retained in the memory, so that even reference to the recorded 

 scales soon becomes unnecessary ; and the ground glass of the camera 

 box has but little use, except to exclude the dust from the interior. 

 In dull weather, the eyes of the operator are relieved from the per- 

 plexing, and sometimes vain search for tlie best focus, and much 

 delicate work may be intrusted to an assistant, who would be most 

 likely to produce unsatisfactory results by the ordinary methods. 

 To those imacquainted with systematic work, the use of such an 

 apparatus may, at first sight, appear troublesome, but it is really so 

 simple that any one may in practice learn its use in much less time 

 than is required to read this description. In fact the whole thing 

 can be comprehended at a glance. 



After some discussion on the merits of this apparatus the meeting 

 adjourned. 



