For the absolute determination of gravity there is today no better method than that of the reversible pendulum, the theory of which goes back to Huygens, and the technique of its use to Capt. Kater, over a century ago. The two determinations involved are those of length and time, and it is the determination of length that limits the accuracy of the measurement. Time can be measured to almost any desired precision if one takes time enough about it, but the measurement of length under the best conditions can not be pushed farther than about 0.1μ in a meter, or one part in 107. With such conditions as prevail in pendulum‐Work it is not likely that the precision can be pushed farther than one part in 1