Installation of tiltmeters
George E. Merritt · Transactions American Geophysical Union · 1934
The tiltmeter is an instrument for measuring changes of level, particularly such small changes in level that great magnification of some sort must be used to make them evident. In the present instrument the powerful method of interference of light is used. By means of this method very small changes in the angle between two surfaces can be measured; hence, if we have one surface that tilts with the surface to be measured and a second surface that remains level we can measure, in a most direct manner, the change of level, or tilt, of any surface upon which the tiltmeter can be set.