STANDARD - Survey Instrument Antique Center!

65
The Surveyor's Solar Attachment.
Written for this catalogue by'H. C. PEARSONS, C. E., Ferrysburg, Mich.
The " Solar Attachment," of which the following is a description, is a modification
of Peat son's Solar Transit.
With the view of reducing the weigh f and cost of this attachment, the declination
arc is dispensed with, using, in its stead, the latitude arc for setting off the declination.
And to attain a greater degree of precision, a small telescope with cross-hairs, and
a diagonal eye-piece have been introduced in place of the lens-bar and focal-plate.
This attachment is an appliance to the surveyor's transit for the purpose of
it becomes
finding the astronomical meridian. Combined with that instrument,
purely astronomical in its character indeed, a portable Equatorial, and an Alt.-
Azimuth instrument combined, hence a few astronomical definitions seem tc
oe requisite.
In the accompanying cut, the instrument is represented in position for an observation
and in north latitude ;
(as in these instructions we will suppose the observer
to be) the view is as from the west.
(1.) The line through the vertical axis of the transit represents the pole of
horizon, and is called the Vertical.
The line perpendicular to this represents the Horizon.
(2.) The transit telescope, having its optical axis in the meridian, and having
its south end (whether object-end or eye-end) elevated so that the vertical-arc reads
the co-latitude, will have its optical axis in the plane of the equator also; viz. the
optical axis of the telescope will then represent the intersection of the plane of the
meridian, with that of the equator. This line is called the Equator.
(3.) The line perpendicular to the equator, that around which the solar
telescope revolves, in following the sun in his diurnal course, is the pole of the
equator. It is parallel with the earth's axis, and is called the Polar Axis.
(4.) The arc distance from the equator to the vertical is the Latitude of the observer,
whence the distance from the vertical to the polar axis, is the Co-Latitude.
It will be observed that these arcs occur alternately around the entire circle; so
that the student should make himself familiar with their relative position with regard
to the horizon, and the vertical, in order to avoid mistakes, when setting the polar
axis of the instrument up to the pole of the equator.