Vacuum-pipeless laser earth strainmeter.

A vacuum-pipeless laser strainmeter has been designed, tested, and is described. The strainmeter has a compensator for the change of the refractive index of air which is determined by Edlén's formula using measured values of atmospheric pressure and temperature. The effect of air-condition change was compensated by the compensator, and residual of the effect was less than +/-5 x 10(-9) for 75 h. The strainmeter has successfully recorded solid tidal strains.