- 
Heller and Brightley.] 1 1 a [May 5th, Is71. 
HELLER AND BRIGHTLEY’S NEw TRANSIT. 
The Engineers and Surveyors’ Transit as at first constructed commonly 
termed a “flat centre,’’ or “Railroad Transit,’ although superior to the 
English Theodolite which it superseded, yet in practice has been found 
defective in the following mechanical details. 
ist. The upper or vernier plate, resting and turning upon the under or 
graduated limb, was accompanied by so much friction, caused by the 
large extent of the rubbing surfaces, that in turning the vernier plate 
around the limb, the whole instrument would sometimes be moved upon 
the lower spindle. 
2d, The oil that was necessarily used to lubricate the plates, would be- 
come so congealed in cold weather that the plates would not move at all, 
and old Railroad Engineers will readily recall the thawing out of their in- 
struments over large fires, at every fall of the thermometer, before they 
could be used. 
3d. The spindle upon which the entire instrument turns, being detached 
from the instrument, thus violating one of the standard rules, that by long 
experience in this country and Europe, has been found necessary in the con- 
struction of any instrument with any pretensions to accuracy, NAV AMR C) 
instrument having a graduated plate and levels should be so constructed 
that both of the centres upon which the instrument turns should be always 
covered and not detachable from the main plates.”’ To prove the utility of 
this rule, it is only necessary after adjusting the levels of one of this class 
of Transits so that they will reverse on the top centre, to clamp the two 
plates together, and turn the instrument on the lower spindle, and the 
levels will invariably be found out of adjustment, showing conclusively 
that through some cause, most frequently the settling of flying dust, etc.,, 
upon the surface and shoulder of the spindle, the spindle is not at right 
angles to the surfaces of the plates. 
Ath. The centre around which the graduated limb revolves can only be 
the thickness of the graduated limb; this centre by reason of its small 
surface wears after comparatively short use, and does not exactly fit the 
conical hole in the graduated limb, and two readings of the same object 
taken without any change inthe position of the instrument have been found 
to differ by 5/, and from no other cause than this. 
These various defects have caused this style of instrument to be entirely 
discarded in city work, and for this another construction is used in which 
the two main plates do not touch each other, thus obviating the two first 
evils, viz.: the friction of the two plates rubbing one over the other, 
and the stiffness of motion of the plates in cold weather. The sockets 
and spindles apon which the main plates revolve being long and fitting 
