PHOTOGRAPHY IN GEOLOGICAL SURVEYS. 227 



will, when the atmospheric conditions are favorable, give valuable 

 results when views of distant objects are required, and it should be 

 added. (In exceptionally rough country it has been suggested that 

 a quarter-plate camera, 4iin. x 3Jin., be used in order to reduce 

 bulk and weight. When this is done a tripod top, known as the 

 " Latimer Clark," should be provided in order to produce the 

 stereoscopic negatives.) 



Plates. — The plate used should be so treated as to be proof 

 against " halation," and under such circumstances as justifiy their 

 use " isochromatic plates " should be employed. Reliable films 

 should not be used, as their manufacture has not yet been brought 

 sufficiently near perfection as to ensure accuracy in the resulting 

 negatives. 



Reproduction of Prints. — The prints from the negatives should 

 be reproduced in carbon or platinum, as prints of this nature should 

 be permanent. 



Nature of Worh. — Two exposures should be made on each 

 subject. When the camera is 6|in. x 4fin. in size, one of these 

 should be a stereo., the lenses being separated to such an extent 

 horizontally as shall be determined at the time (a record of this 

 distance being kept), and a 6^in. x 4^in. negative taken on the 

 second plate, including either the same angle as the stereo, exposure 

 or such other angle as may be deemed desirable, but in taking it 

 the camera should be pointed in the same direction as for the 

 stereoscopic negative. The front of the camera must possess means 

 for altering the distance between the centres of the lenses laterally. 

 The half-plate negative may be printed from, and the print mounted 

 so as to allow of examination as a diagram, the prints from the other 

 negative being trimmed and mounted in the usual manner for the 

 lenticular stereoscope. The photographs of all fossils should also be 

 executed so as to form subjects for the stereoscope, though in this 

 case often the stereo, negative will be found sufficient. A scale 

 should always be attached, so that the actual size of the fossil can 

 be seen. Sufficient reasons for the photographing of the subjects 

 in this manner were advanced in the paper read at the Hobart 

 meeting by the Secretary to this Committee, and an additional 

 reason is that, should any accident happen to a plate in transit, the 

 other always remains to be rr.ade use of. In all cases the very 

 best technical work is absolutely necessary ; no wrongly exposed 

 or carelessly developed negative should be allowed to find a place 

 in the collection, and in order to make certain of this photographers 

 of the greatest ability and experience should be chosen to do the 

 work. '1 hese men will in many cases be found already in the 

 Civil Service of the colonies, so that, if their services are availed of, 

 no extra expense to the State will be involved. 



Field Work. — In making a set of photographs of a particular 

 district a plan of the locality should be set down, and the various 

 photographs which have been taken from points within its ai'ea 



