PHOTOGRAPHY. Ill 
by which ;m almost hopeless field exposure can be made to give cred- 
itable results, a dim pencil sketch be reproduced on any desired scale, 
or a fossil brought out so as to eliminate all effects of color and show 
only its form and markings. 
The photographic laboratory of the Geological Survey is equipped 
with the most modern appliances. Daylight exposures are no longer 
made, so that the work of copying maps progresses regardless of sun- 
shine. Two large cameras are used in this work. The maps to be 
copied are stretched on adjustable frames attached to the walls, each 
illuminated b} T two powerful 1 arc lamps which are operated by the 
photographer from his position at the camera. The camera rolls on 
tracks and may be elevated or depressed or moved forward or back* 
ward for focusing or for procuring reductions to hxed scale, all from 
| one position behind the instrument. In like manner, printing is no 
longer dependent upon sunlight, but the negative to be printed is 
held under pressure in a quick-acting frame on trucks, on which it is 
tilted so as to expose it to an electric light for a few seconds, after 
which the frame falls back into position and flies open, when the print 
is removed and a new sensitized sheet is inserted. This process is so 
rapid that as many as 150 prints from a negative have been made in an 
hour. 
In the Geological Survey photography readily groups itself into 
field work and laboratory work. It is all under control of a chief 
photographer, whose powers differ in each branch of the work. To 
the person using a camera in the field he gives instruction and advice, 
sees that the instruments purchased are such as are best adapted to 
the desired work, and that they are kept in repair and issued on proper 
requisitions. Here his functions cease. He can neither select the 
views, place the camera, nor time the exposure. He must accept the 
results brought to him by the field force of the Survey, upon whom 
the only restriction placed is that the subjects photographed shall be 
germane to the work in hand. Generally the exposed negatives are 
sent to the Survey laboratory for developing, but frequently the user 
of a camera develops his negatives in the field, or has them developed 
by a local photographer, in order that the results may be immediately 
known. It often happens that such work is poor, judged by the 
standard established in the laboratory, but probably the advantage of 
immediately knowing whether a negative of sufficient value to be used 
has been procured more than compensates for the inferior quality. 
A record of all exposures made in the field is kept according to 
forms arranged for the purpose. These forms give a brief description 
of the locality and subject, condition of light, length of exposure, 
aperture of lens, and the field number of the negative, and must 
accompany all plates or films sent to the laboratory from parties in 
the field or turned in on their return. They furnish the data from 
