THE ROYAL ARTILLERY INSTITUTION. 
163 
27. In addition to the foregoing arrangements, a small portable wooden 
hut has been constructed, in order that the instrument may be moved from 
place to place, Eig. 10. 
The hut has a half-flooring, and the table on which the instrument rests, 
stands upon the natural ground, without touching the hut. A movable 
cable has also been constructed to accompany this hut. This cable unrolls 
itself off a travelling axle, and can lie on the ground while the ends are 
attached to the frame targets and the instrument. 
I have found this arrangement of the greatest use, as the instrument can be 
moved to any gun which may happen to be of such a size, or in such a 
position, as to make its removal inconvenient. 
28. I have had considerable experience in the use of Major Navez's 
delicate and beautiful little instrument, and can speak from personal know¬ 
ledge of its great accuracy when skilfully manipulated. 
The following are the chief points to be attended to :■— 
Any error in the adjustment of the pendulum is easy of correction; the 
principal thing to be looked to being the distance of the washer from the 
poles of the large electro-magnet, and the amount of play allowed to the 
oscillating system. This has been explained already. 
Of course every part of the instrument must be kept quite clean, and free 
from dust or grit. 
In the disjunctor care must be taken that the platinum pointed screws are 
near enough to one another, and that when the instrument is cocked one 
blade is not in advance of the other. 
The chief source of error lies in the conjunctor; the mercury must he per¬ 
fectly pure, and during a long day's experiments it would be well to change 
