Y level for plane table surveying
Date: circa 1920
Inventory Number: 1997-1-1669
Classification: Surveyor's Level
Subject:
Maker: C. F. Casella & Co. Ltd. (founded 1905)
Cultural Region:
Place of Origin:
Dimensions:
12.8 × 10.2 × 35.6 cm (5 1/16 × 4 × 14 in.)
DescriptionBrass Y level mounted on three feet for plane table surveying.
The body of the telescope tube is covered in black enamel. The eyepiece tube is in exposed brass, while the eyepiece itself is black with knurling around its edge. Clamped around the eyepiece tube is an enameled brass piece with two short arms. One arm has a screw at its end, the other a hole for a similar screw.
Clamped around the telescope tube are two brass rings to protect it from contact with the mount's Y arms. Bolted perpindicular to the telescope tube near the end opposite the eyepiece is a small bubble level. The level has an oval glass window with two black lines on either side of the center of the window. Two exposed pins project upward from the bubble level, one on each side of the window.
The level is supported by a T-shaped mount with a mottled green surface and two Y standards. Projecting down from the two points of the short arm of the T are two brass points covered in black enamel. A brass leveling screw with a knurled knob projects down from the end of the long arm of the T. A brass pin projecting from the side of the long arm of the T secures the leveling screw at the top. The point of the leveling screw is heavily corroded.
The body of the telescope tube is covered in black enamel. The eyepiece tube is in exposed brass, while the eyepiece itself is black with knurling around its edge. Clamped around the eyepiece tube is an enameled brass piece with two short arms. One arm has a screw at its end, the other a hole for a similar screw.
Clamped around the telescope tube are two brass rings to protect it from contact with the mount's Y arms. Bolted perpindicular to the telescope tube near the end opposite the eyepiece is a small bubble level. The level has an oval glass window with two black lines on either side of the center of the window. Two exposed pins project upward from the bubble level, one on each side of the window.
The level is supported by a T-shaped mount with a mottled green surface and two Y standards. Projecting down from the two points of the short arm of the T are two brass points covered in black enamel. A brass leveling screw with a knurled knob projects down from the end of the long arm of the T. A brass pin projecting from the side of the long arm of the T secures the leveling screw at the top. The point of the leveling screw is heavily corroded.
Signedstamped on telescope tube, center: CASELLA LONDON
FunctionFor use in plane table surveying, to measure contours.
After placing the Y level, on a plane table, at his starting location, the user levels the instrument by means of the spirit level and the leveling screw. (Note: Y levels typically have a bubble level running parallel to the telescope tube for use in leveling the instrument. This may be what the bracket on the eyepiece tube is for, or an interior level visible through the eyepiece may serve this same purpose.) Then he sights a stadia rod through the telescope, moving the rod as needed until the target is centered behind the telescope's cross hairs. The difference in height between the telescope and the rod target indicates the gain in elevation over the horizontal distance between the two.
After placing the Y level, on a plane table, at his starting location, the user levels the instrument by means of the spirit level and the leveling screw. (Note: Y levels typically have a bubble level running parallel to the telescope tube for use in leveling the instrument. This may be what the bracket on the eyepiece tube is for, or an interior level visible through the eyepiece may serve this same purpose.) Then he sights a stadia rod through the telescope, moving the rod as needed until the target is centered behind the telescope's cross hairs. The difference in height between the telescope and the rod target indicates the gain in elevation over the horizontal distance between the two.
Curatorial RemarksThough originally identified as a transit, the best guess is that this is a Y level for use with a plane table.
It was impossible to find such instrument in catalogs or online. It does have the Y-shaped arms typical of Y levels, but is missing the parallel spirit level that are seen in other Y levels. See note under function.
See a nearly identical Casella Y level with a different eyepiece, 1997-1-1670.
It was impossible to find such instrument in catalogs or online. It does have the Y-shaped arms typical of Y levels, but is missing the parallel spirit level that are seen in other Y levels. See note under function.
See a nearly identical Casella Y level with a different eyepiece, 1997-1-1670.
