STANDARD - Survey Instrument Antique Center!

140
The Telescope will be invariably inverting in order to admit of as large an aperture and as high a powei
as is possible. Thus : its aperture will be i
J inches, the total length is about 17 inches, and it will have a
of i to 100,
magnifying power of 40 diameters. It will be provided with fixed stadia wires, in the proportion
the distance to be measured Irom a point in front of the objective equal to its focal length
The Spirit Level is of the single reading kind, and is generally made so that one division (of -rV of an
inch) equals from 8 to 10 seconds of arc. The sensitiveness of the level will, however, be adapted to the particular
requirements. It is not necessary, however, to have it any more sensitive than is required for a fine
field instrument, as an over-sensitive level is apt to give more trouble than benefit in its use.
A Reversion Level of same sensitiveness might be applied instead of the single reading level, if desired,
as a convenience (see Reversion Level p. 136), when the highest precision is not needed. Of course in fine work
the reversion level must be used in the direct position as with a single reading level. However, one will understand
that a reversion level is very apt to change its true barrel form in time thus becoming wholly
unreliable, and therefore we do not advise it at all, and particularly not for an instrument of such a fine
character as this is.
A Metal Mirror will be furnished with the instrument, attachable to either side of the level, enabling the
operator to read the bubble without stepping aside a convenience which will be ; appreciated when working on
shaky ground.
Adjustment. The adjustment of the telescope and the level must be made precisely as in an ordinary
wye level. (See adjustment of the wye level, pages 59 and 63 of this hand-book ) The spirit level will be in
thorough adjustment when the telescope with its sunshade attached is focussedfor a distance of about 400 feet,
when the telescope is in perfect balance and the equality of the collars is assured thereby ; for shorter distances,
however, there is a small error due to the unbalancing of the telescope caused by the object slide being thrown
out. Small as this error may be it can be entirely eliminated by simply bringing the bubble to the center by
the use of the micrometer screw.
Explanation. The foregoing has been written at some length to give a clear understanding of the principal
features of this instrument. Naturally, the question may now present itself, why not use a striding level
alone, in place of the fixed or reversion level, as is done in some of the best types of instruments, particularly
as the pivot arms, extending from the middle of the cross-bars, must necessarily be spread quite a distance
apart, to readily permit the revolution of the telescope with the fixed level in the wyes. To this we may say,
that a fixed level placed below the telescope, where it is guarded against breakage and, in a measure, from the
action of the sun, is better adapted to the wants of the Civil Engineer in running quick and accurate levels
in cities, towns, etc., than a striding level with its more cumbersome features and manipulations would be,
particularly if the work was to be of the most precise character.
It is only when the collars of a telescope are badly worn or imperfectly made that the striding level has
any advantage over a fixed one. As a rule a fixed level keeps in better adjustment, is simpler to manipulate
than the striding level, and is free from the errors due to the uncertainty of contact of the collars and the wyes.
Moreover, the construction of the new instrument is such that it has a greater stability than those of previous
make. We therefore believe that the fixed level has as legitimate a standing as the striding one.
For the above and similar reasons the American Engineers have and will give preference to the instru
ment which has the level fixed to the telescope; and this has led us to the adoption of this feature in our new
instruments. This idea is also prevalent among the best instrument makers and engineers in Europe, as may
be seen by examining Prof. Nagel's published description of a similar instrument.
Instrument, Finish, Packing*, Weight, etc. The telescope is leather-finish,
while some of the more bulky parts of the instrument are simply treated either with
cloth finish or japan, in order to lessen the cost No attempt will be made to give an
elaborate finish at the expense of accuracy and utility ; altogether, as all the other
parts will be bronzed and lacquered in a manner customary with us, it will present a
handsome appearance. This instrument is packed erect in one box in the same manner
as we pack the regular engineer's wye level. It is secured to the tripod in the
same manner as are all of our instruments with three leveling screws. (See page 136
for description )
The mahogany box contains a sunshade, wrench, screw-driver and adjusting pin.
Weight of instrument, !!- pounds; weight of tripod, 10-J pounds; weight of mahogany
box, 10| pounds ; gross weight of instrument complete, securely packed in two
boxes for shipment, 60 Ibs.
Price of this instrument, inverting telescope, leather-finish, fine
mirror mounted in case, fixed stadia wires, and a single reading fixed
spirit-level,
... $215.OO
Extras to Engineers' Precise Level
Center of instrument made of steel, and hardened and running in a socket of
cast iron, improved style (see cut, page 135), .... 15.00
Sunshade with smaller aperture, for use with the telescope when the sun
rays are too bright for accurate work,
1.00
Gossamer bag, to protect instrument. .... ... 1.00
Bottle of fine watch oil for lubricating the centers, etc.,
0.35
t If geodesic work is to be done, , higher sensibility might be permissable, but our customary fluid would be sluggish in
ave to be filler! with pure ether, in order to make it
,
quick acting (see pages 7, *8, 38).
An air chamber would be necessary to allow for adjustment of the bubble, which in this case changes its length rapidly for
sltehr perature. By adding a chamber, a feature is introduced which is liable to affect the reliability of th
changes in temperature. By adding
Spirit level and entail extra expense
Code Word. Engineers' Precise Levi bnt witn steel centre Arethusa