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HINTS TO TRAVELLERS. 
4. The photographic method can be conveniently used in conjunction 
with more ordinary methods. No matter what method is chiefly used it 
must always happen that details between fixed points have to be filled in 
from sketches or photographs or by estimation on the spot, and no doubt 
survey photographs will always be useful to help to fill in details in an 
ordinary survey. 
5. Survey photographs can be conveniently used to check field work and 
detect important mistakes where such have been made, and in any case 
they will serve as corroborative evidence of the accuracy and completeness 
of work done. By no other means can important errors be rectified, 
except by revisiting the ground, which may sometimes be very in¬ 
convenient or impossible. 
6. It is always useful to know the general aspect and appearance of a 
country traversed. Ordinary photographs may suffice to give some 
general impressions, more or less accurate, but they cannot compete with 
a systematic series of good survey photographs. 
7. A set of good survey pictures from well-selected stations, the exact 
positions of which are known, will always form a valuable record for 
future reference, and would afford most useful information to future 
travellers in the same country. 
Most of these advantages are self-evident, but until recent years it has 
not been easy for travellers to profit by them, partly because it has been 
difficult to obtain really efficient instruments for photographic survey 
work, and partly because there were no good practical text-books to 
instruct beginners concerning the practical details of the photographic 
method. These obstructive difficulties have been now, to a large extent, 
overcome. 
Good photo-surveying instruments can now be purchased for about 
£15 or £50, which can be trusted to yield good reliable photographs 
from which maps can be drawn. The best instruments yield pictures 
which bear on their faces automatic records of nearly all the information 
which is necessary to enable anyone who understands map-making to 
draw maps from them. 
Eig. 1 is an illustration reproduced from ‘ Engineering J of one of those 
instruments known as the Bridges Lee photo-theodolite. 
Essentially, the instrument consists of a fixed focus stand camera with 
accurate levelling adjustments and mechanism inside the box for record- 
