Sphe-rom′e-ter.
An instrument for measuring the curvature of surfaces.
It consists of a threearmed frame, standing on three steel pins, which form with each other an equilateral triangle; in the center of the instrument is a vertical screw with a fine thread, and having a large graduated head.
The screw is turned downward until its point reaches the surface on which the instrument stands; if this is a true plane, the index of the graduated screwhead should mark zero; if, on the contrary, it is either convex or concave, the corresponding positive or negative reading indicates the degree of sphericity.
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Spherometer. |
Fig. 5379 is an instrument for measuring the curvature of lenses or speculums or of the tools for grinding them.
The arm
a has two branches
b b, whose ends are accurately turned and ground to a circular form.
The socket
e contains a sliding indexbar
d with conical ends, which is divided to fiftieths of an inch; a vernier
e enables it to be read to 1/1000 of an inch, or by estimation, to 1/2000.
