112 THE UNITED STATES GEOLOGICAL SURVEY. [bull.227. 
which is made a permanent office record of all negatives that are of 
sufficient value to be preserved. 
All work in the laboratory is done in pursuance of card requisitions 
made by the division or section chief, countersigned by the chief clerk. 
This requisition specifies the character and amount of work to be done 
and the use for which the thing required is intended, and must be 
accompanied by the subject to be photographed. Upon its receipt by ; 
the photographic section the card is given a serial number and filed, 
and the requisition is then referred to the proper subsection, to await 
its turn. When the work is completed the card is returned to the per- 
son making the requisition, accompanied by the thing' required, who 
inspects it and receipts for it on the card, which is then filed for a 
permanent record. 
The work done in the laboratory falls into four general classes — map, 
dry plate, specimen work, and printing— and to each of these classes 
experts are assigned. 
If the requisition calls, for the reproduction, on either the same, an 
enlarged, or a reduced scale, of a field map, a county or State map, 
or some rare chart of early explorations, it is assigned to the map sec- 
tion. Here cameras accommodating plates up to 31 by 31 inches in 
size are used, and the negatives are made by the wet process. These 
cameras are mounted on tracks and are worked by slow movement, so 
that prints of the exact size required can be obtained. In this section 
two men are constantly employed in making negatives and one in 
washing and preparing glass. If the requisition calls for the devel- 
oping of plates or films, it goes to the dry-plate section, where two 
men are engaged in this work. If a fossil or mineral is to be photo- 
graphed, it is referred to the specimen section, where photo-micro- 
graphic and other special apparatus is used. After negatives are made 
or developed they are turned over to the printing section, where the 
specified number of prints are made upon the paper desired. If a 
negative is of sufficient importance to be preserved, a permanent num- 
ber is given it and it is filed for future use. Prints from such nega-, 
tives are preserved for ready inspection in indexed albums, and more 
copies are made as desired. 
The photographic section has now on file about 25,000 negatives and! 
nearly 4,000 lantern slides. A considerable number of the negatives! 
were made by the Powell and Hay den surveys, and constitute aninval-l 
uable record of early explorations. The remainder were made by the! 
Geological Survey 7 , by far the larger part since the introduction of the 1 
dry-plate process. At the organization of the Geological Survey one! 
photographer and one assistant were employed, and these were engaged 
almost exclusively in field work. In 1903 the force consisted of a sec- 1 
tion chief and 8 assistants, employed almost exclusively in the labo-l 
ratory, while about 75 cameras were used in the field. To obtain a just I 
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