AMUstmeKTs of the tMeodoLiTF. 31 
bubble of the telescope level to the middle of its run by turning the clip 
screws. The instrument will now be in adjustment and ready for use. 
All first-class instrument makers are very careful, for the sake of their 
reputation, to see that the theodolite is in perfect adjustment when it 
leaves their hands, and, with the careful treatment which this instrument 
should always receive, is not likely to get out of order; it is, nevertheless, 
necessary from time to time to test these adjustments. 
Observations with the Transit Theodolite should always be taken 
in pairs, with the vertical circle first to the right and then to the left , 
and the mean of results should be taken. When a diagonal eye-piece 
is used for observing altitudes of the sun, the lower limb has this ap¬ 
pearance 
LOWER LIMB. 
and the upper limb this, jmrIumb. . When observing 
altitudes of the sun with the inverting telescope, it must be remem- 
bered that what appears to be the lower limb is really the upper, 
thus: 
di 
and 
UPPERj LIMB. 
limb. . Where the direct telescope is used the 
XT. 
reverse is the case. 
Another form of transit theodolite, in which the level A is carried 
on the vernier arms instead of being attached to the telescope, 
is shown p. 32. The magnetic needle B is also attached to the 
instrument in a different manner, being in all respects similar to the 
one used with the plane table, and is described p. 42. This is so 
constructed that it can be attached, by the hooks C C C, to the under 
part of the instrument. The adjustments of this instrument are 
identical with those previously given for the more common form of 
transit theodolite,* with the exception of that for the vernier arm level 
A, which is adjusted in the following manner:—First set the instrument 
carefully by the levels on the vernier-plate, and then by means of the 
clip screws Z Z bring the bubble of the level, A, on the vernier arms 
to the middle of its run. Next unclamp the vertical circle and place 
* See note, p. 29. 
