PROGRESS REPORT ON THE SYSTEMATIC CONDUCT OF THE 

 PHOTOGRAPHIC WORK OF GEOLOGICAL SURVEYS. 



Members of Committee. 



Owing to the great distances by which the centres of the various 

 colonies are separated, the members of this Committee have had no 

 opportunity of meeting and exchanging their views in the ordinary 

 manner. The draft report was submitted to each of them, and it 

 has been deemed prudent to place on record such of the items as 

 have been adojited, leaving the remainder to be dealt with in 

 the next report. The work hereinafter nuticed is that of the 

 photographing and reproduction of objects of purely geological 

 interest, but in the following report the application of photography 

 to topograjihical surveying will be introduced, and a simple and 

 systematic method of conducting a survey by means of the camera 

 will be described. 



Apparatus. — This should be in all particulars as near perfection 

 as it is possible to make it. The camera (at any rate all the main 

 working parts of it) should by preference be made of metal, and 

 should be constructed so as to work with extreme accuracy; no such 

 accessories as swing back, swing front, or side swings are allowable. 

 The tripod head should be large, so as to ensure rigidity, and should 

 be so constructed as to admit of being levelled in the same manner 

 as a theodolite, and it should always be carefully levelled previous 

 to making the exposure. A comjjass shoidd also be attached, so 

 that the direction of any view can be determined. The size recom- 

 mended is what is known as "half-plate" (4|in. x 6|^in.), this being 

 a reasonable and useful size for practical work when ordinary flat 

 photographs are used ; at the same time it lends itself admirably to 

 the production of stereoscopic work, and, again, it is a size always 

 in the market. Lenses of "symmetrical" or "rectilinear" pattern 

 must be used in order to avoid ditstortion. and the equivalent 

 focal length of each lens must be accm-ately determined, and this 

 together with its "optical centre " should be engraved on the 

 mount. Several pairs of lenses of different focal lengths siiould be 

 attached to each outtit. The recently-introduced " tele-photo." lens 



