John Locke, in U.S. patent 7447 dated July 2, 1850 , describes the basic design for the hand level. The target is sighted directly with no optics. A lens in the form a 1/2 circle is used to focus the bubble. After this patent expired many "Locke" hand levels were made.
I think this is a very early hand level made by K & E. The main tube has a square cross section of about 0.57" x 0.57". In the photo above the right hand 1/2" square portion is designed to slide in and out of the main square tube and by so doing the line of level can be adjusted. Stamped on the top surface is "KEUFFEL & ESSER CO. N.Y. Since K&E started in business around 1876 this design probably was made to get around the Locke patent.
This is an image aligned at 45 degrees of the center reflector. The right hand portion with the 45 degree bevel toward the eye end (at the very left) has a silvered surface at the center that acts as a mirror to allow viewing the bubble from below at the center line.
Looking back into the front right hand part there is a horizontal metal vane that acts as a cross line to mark the target. There are no optics, other than the first surface mirror. The eye hole has threads (Why?) with an I.D. of 0.168".
If you know anything about this level email brooke(at)pacific(dot)net.Operation
As far as I can tell there are no lenses in this instrument. If I wear my reading glasses I can see the bubble, although out of focus, and can accurately center it vertically on the horizontal reference line formed by the sheet metal vane at the front of the instrument, but the far objects are blurry. If I don't wear my reading glasses there is a bright spot where the bubble is located, but the horizontal cross line is about invisible.Moving the front piece back and forth will allow the largest bubble image to be centered on the horizontal line and does not change the level line.
After the Locke patent
expired K&E started making their version. That's why there is
no patent info on it.
This level is not marked N5702, but I think that is the
pattern. Just marked Keuffel & Esser C0. N.Y.
Note that the front "glass" is not a lens, just a glass to keep the
inside clean. Also there is a rear "glass". There is a 1/2
circle lens about 2 1/2 inches from the eye hole that allows your eye
to focus on the bubble when it is also focused at infinity to see the
target. It's not
clear how the sight line is calibrated to be level.
This is very similar to the hand level used by my Uncle, Charles Carrithers, to check lath stakes when leveling land. In addition to the level he had a lath on the tractor with a notch, maybe 3 feet up from one end. The laths driven into the ground by the surveyor had a horizontal mark 3 feet above the desired grade. So if he saw the mark from the ground where he was sighting then the grade was correct. If not he would know how much to cut or fill.
There are other Locke pattern hand levels made by K&E that have the model number N5702 or N5703, I'm not sure of what differences there are between these.
Note that an Abney hand level is also called a clinometer. It is different than the Locke hand level in that it has a vertical scale to measure the inclination of the instrument.
There seem to be a number of different K&E hand levels:
The square tube versions allow resting the level on a bench or other support without it rolling. Also some of the square tube versions have the 90 sighting feature.
Kuker
Marked: PAT 1741422, KUKER-RANKEN INC, SEATTLE
1741422 Hand Level Dec 21, 1929 O. J. Kuker 356/249
Weber
"Weber Phila No 6160" is a 5" long when collapsed and 5 1/2" long extended hand level with a 13/16" diameter round tube.
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