128 
HINTS TO TRAVELLERS. 
identical in construction, and the internal mechanism designed by Mr. 
Bridges Lee for giving automatic records on the picture is the same. 
It may well happen that before this edition of f Hints to Travellers ’ is 
exhausted other makers may enter the field with efficient but cheaper 
instruments, and further improvements may be designed, so that anyone 
thinking of adopting the photographic method in practice would do 
well first to consult the Instructor in Surveying to the Royal Geographical 
Society or Mr. Bridges Lee, either of whom will probably know where 
the best instruments can be obtained at the lowest price at the time of 
enquiry. 
Fig. 2 is reproduced from a photograph taken in North Wales by 
Mr. Cripps Matheson, with an instrument fitted with Mr. Bridges Lee's 
automatic recording mechanism. 
Work in the Field. 
A traveller duly equipped with a photographic surveying outfit should 
select his stations and fix their exact positions on his skeleton map on 
the same general principles and by the same means as he would adopt 
if he were making a plane table or other kind of survey. He must 
continually keep in mind the fact that to obtain an accurate map he 
must have good intersections for all his principal points. Also he must 
make sure that points, the positions of which he wishes to fix accurately, 
are clearly visible from two stations at least, remembering that the lens 
is the point of vision for the picture. A fair knowledge of the general 
principles of surveying is necessary, and also a sufficient knowledge of 
photography to insure getting serviceable pictures. Artistic pictures 
are not necessary, but every effort should be made to get pictures 
sufficiently clear and sharp to yield good enlargements. 
The instrument should be carefully set up,at the station and accurately 
levelled and used as described in the book of instructions generally 
supplied with it. Generally some three or four views at a station point 
will suffice for all practical purposes. Sometimes it may be advisable to 
obtain a complete round of views. 
Before leaving the station suitable note-book entries should be made, 
and if any other surveying instruments are at hand a few direct observa¬ 
tions may be made with them and noted if time permits. 
