2U 
JOURNAL OF THE PLYMOUTH INSTITUTION. 
SURVEYING BY PHOTO GKAPHY. 
ABSTRACT OF LECTURE BY MR. W. G. TWEEDY, B. A. 
(Read January 22nd, 1880.) 
The lecturer began by stating that for many years he had believed 
surveying by photography to be the process of the future, but that 
until recently the conditions necessary to make the process practical 
in the field had been lacking. This had been supplied during the 
past year. By means of the gelatino-bromide process, dry plates 
were produced that had but one fault — they were almost too 
sensitive ; and he had there for inspection pictures taken in the 
sixty-fourth of a second, measured time. There were now many 
makers of such plates, and they could be purchased, ready for use, 
at a cheap rate. 
As long ago as 1862 the lecturer invented a revolving camera, 
by which a picture in cylindrical projection could be taken on a 
flat plate of glass, including, if necessary, the whole sweep of the 
horizon in one continuous view ; and in March, 1863, he published 
a complete description of the invention, signed W. G. T., Plymouth, 
in the Photographic News, and deposited some pictures taken by 
the instrument in the hands of J. H. Dallmeyer, the eminent 
optician. Copies of some of these pictures were on the table. In 
October of the same year Mr. J. E. Johnson took out a patent for 
a similar invention to that which the lecturer had described more 
than six months before. Mr. Johnson called his the " pantascopic 
camera," and it corresponded in every detail with the lecturer's. 
This was another example of simultaneous invention, but the 
lecturer claimed the contrivance as his, by virtue of prior publica- 
tion. 
At that time the w r et collodion process was the only satisfactory 
one, and surveyors, even if they appreciated the powers of the 
" pantascopic camera, " would have required the services of a 
professional photographer and a waggon-load of apparatus, so the 
