spherometer

The glass is ground with emery to the correct spherical figure as given by a spherometer.

It is well to control this process by means of a spherometer, so that the desired radius may be approximately reached.

Before the grade of emery is changed all three surfaces must agree, as nearly, at least, as the spherometer will show.

The squares of glass are cemented to the roughing tool, and this is ground to the spherometer by means of the counterpart tool.

Here is a very fine spherometer that Dr. Hastings works with from time to time, and which he calls his standard spherometer.