38 
HINTS TO TRAVELLERS. 
The same process would have to be gone through to find the value of 
a division of the Left Micrometer. 
In combination with this instrument a rod of known length is generally 
used. Fig. 2 represents a rod devised by Lt.-Col. St. G. C. Gore, R.E., 
Surveyor-General for India. 
Fig. 2 . 
The bar is made of hard wood in three sections. The central section is 
square in cross section If" x If" with iron sockets six inches long, g, g , 
at each end, into which the outer portions of the bar fit, being pinned into 
place by the pins g'. The outer ends of the bar carry iron sockets, h, h, 
which have the recesses in them accurately machined out. Into these 
sockets the discs i fit by means of carefully fitted hooks on their backs. 
The discs are of wood ten inches in diameter, painted white with a black 
ring. Black cloth covers are also carried to fit t’ghtly over the discs, in 
case of working with a light background. 
In the centre of the bar is a brass socket plate, by means of which 
the bar can be attached to a tripod. 
The sighting arrangement consists of a light iron frame, hinged at 
e, b und Jc . The pin of the hinge b carries a point on the top, and a 
similar metal point; is fixed at a in the centre of the bar. The end of the 
