STANDARD - Survey Instrument Antique Center!

136
18" HYDROGRAPHER'S WYE LEVEL
Having a three-screw* leveling base with arms of greater radius* *
(3-inch) to afford maximum stability when exposed to wind pressure
and to better control the spirit level of this instrument.
The instrument shown on opposite page has the upper part, viz: cross-bar, telescope
and level exactly similar in size and style to our regular Engineers' 18" Wye
Level (page 134) except the telescope which in this instrument is mostly of the inverting
kind. If an erecting telescope is desired we will be pleased to furnish it, in which
case the aperture will be the same but the power will be 35 dia. only. As regards the
mode of securing the instrument to the tripod by means of the fastener, see cut and description,
page 46, in article, "Shifting Center."
This fastener is very simple and even in the coldest weather easy to manipulate.
It adds very little to the weight and secures the necessary stability in taking up all
back lash of the leveling screws after wear. It is better than any other device
that we know of to achieve this end.
The tripod bolts are the same distance' from the center as the leveling screws.
Made to order only
SPECIFICATIONS:
Telescope; objects inverted, aperture 1 3/ inch, power 40 dia.; focussing slide
very long and protected by dust guard; collars hard bell metal; line of collimation
correct for all distances; telescope balanced each way from center when
focussed for a mean distance with sunshade attached to secure highest accuracy
attainable; stop provided so that the cross wires will always be horizontal and
vertical in instrument.
Eye-piece perfectly achromatic with large, flat field of view; provided with
an improved screw arrangement permitting to focus the wires by simply turn-
ing its head to right or left.
Center of hard bell metal is large in dia., long, strong and unyielding.
Spirit Level 8^/3 inches between centers of suspending arms. Sensitive ness is
8 to 1O seconds of arc for one tenth inch of the scale, (unless otherwise spec-
ified).
Mahogany box provided with strap, lock and hooks, contains sunshade, wrench,
screwdriver and set of adjusting pins.
Weight of instrument about 12 Ibs. Weight of split-leg tripod about ] 3 Ibs.
Gross Weight securely packed for shipment in two boxes about 60 Ibs.
Code name Andromeda Price as above $158.OO
Extras to Hydrographer's Wye Level.
Stadia wires fixed ........... $3.00
Steel Center running in a cast iron socket to insure freest motion with perfect
fit
Fine mirror mounted in metal frame with universal joint. (This is readily
attachable to either side of the instrument and facilitates the reading of
the bubble on soft ground without stepping aside). ..... Extra sunshade with smaller aperture for use with the telescope when the
sun's rays are too bright for accurate work ...... Gossamer water-proof bag, to protect the instrument in case of rain or
15.OO
10.00
1.50
dust i.oo
Bottle of fine oil to lubricate the level center 0.35
Prior to 1888 we have sometimes placed upon this instrument an adjustable wye
with a micrometer screw arrangement for the pointing of the telescope and setting of the bubble
independently of the leveling screws. The very marked wear on the collars at the point of
contact in the wyes when the telescope is moved in altitude has induced us to abandon this feature.
A perfect instrument in this line and at the same time entirely free from any change in height when
the micrometer screw is extensively used during an extended leveling operation is our Engineers'
Precise Level, page 139. This latter instrument is capable of the most precise work and is offered
at a price so very low that it should be included in the instrument equipment for precise leveling
of any magnitude.
To prevent a change of height, after an appropriate leveling of an instrument with three
leveling screws, it is advisable to clamp one of the leveling screws by its clamp screw at the side,
and to level up by the other two screws alone. This should be done in like manner, also, to correct
for slight changes in the level caused by the settling of the tripod-legs.
* Four leveling screws commend themselves in the more ordinary class of instruments for
the greater rapidity with which an instrument can be leveled up approximately, and that (no matter
how much the leveling screws may be worn) when brought to a true bearing on the lower leveling
plate, all such looseness is taken up.
**NOTE: In some types of leveling instruments numnted on a three-screw leveling base the
latter is often too small for the length, power, height and weight of the instrument, making it top
heavy, thereby rendering it unsteady and unsuitable for close work.