ON A GOOD DIFFEREiNTIAL CKAVITT METER. 41 



Second Report of the Committee, consisting of Greneral J. T. 

 Walker, Sir William Thomson, Sir J. H. Lefroy, General 

 K. Strachey, Professors A. S. Herschel, Gr. Chrystal, 

 C. NivEN, J. H. PoYNTiNG (Secretary), A. Schuster, and 

 Gr. H. Darwin, and Mr. H. Tomlinson, appointed for the 

 purpose of inviting designs for a good Differential Gravity 

 Meter in supersession of the pendulum, xvherehy satisfactory 

 results inay be obtained at each station of observation in a few 

 hours, instead of the many days over tuhich it is necessary to 

 extend pendulum observations. 



Since the last report the Committee have received an account of a 

 proposed instrument from Mr. C. V. Boys. Mr. Boj's has lately found 

 that quartz threads, which he is able to drav/ from melted quartz, are 

 remarkably free from ' fatigue,' and he intends to make use of this in 

 constructing a torsion gravimeter. In the form which seems to be most 

 promising a quartz thread is stretched horizontally, and to the middle of 

 it is attached one end of an arm going out at right angles with a mass at 

 the other end. The thread is twisted and the arm is drawn out of the 

 horizontal position till it is nearly in unstable equilibrium, and the 

 arrangement is exceedingly sensitive to small changes in the weight of 

 the mass. In principle the instrument resembles other applications of 

 horizontal torsion, such as those in some forms of Sir W. Thomson's 

 attracted disc electrometers. As Mr. Boys is engaged in experimenting 

 on the best form of instrument, we do not give more than the foregoing 

 sketch of his proposals. 



As the metal spring which Sir William Thomson proposed to use 

 (described in last year's report) appears to be subject to ' fatigue ' in a 

 much greater degree than Mr. Boys's quartz threads, he is awaiting the 

 results of Mr. Boys's experiments before proceeding with the construction 

 of a complete instrument. 



The Committee ask for reappointment, with the addition of Mr. Boys, 

 and they apply for a grant of lOZ. to aid in the construction of an 

 instrument. 



Report of the Committee, consisting of Professors Williamson, 

 Armstrong, Dixon, Tilden, Reinold, J. Perry, 0. J. Lodge, 

 BoNNEY, Stirling, Bower, D'Arcy Thompson, and Milnes 

 Marshall, and Messrs. W. H. Preece, Vernon Harcourt, 

 Crookes, Topley, and E. F. J. Love (Secretary), appointed 

 for the purpose of considering the desirability of combined 

 action for the purpose of Translation of Foreign Memoirs and 

 for reporting thereon. 



This Committee have held two meetings, and carefully discussed the 

 subject submitted to it by the British Association. The result of the 

 discussion is expressed in the following resolution of the Committee : — 

 ' That, owing to the difficulty of making suitable selection of the 



