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PROFESSOR CHRYSTAL AND MR JAMES MURRAY 



The Counterpoise. — This need not be more than a few ounces in weight. In form it 

 should be narrowly cylindrical, so as to offer little resistance to the wind. Some 

 serviceable weights were made by twisting small coils of lead wire. 



The Pulley. — A pulley of 2 inches diameter was taken as the standard. A groove 

 served to keep the line in place ; the diameter of the pulley was measured from the 

 bottom of the groove. A steel axle rested on brass or steel bearings. The first instru- 

 ment made had friction wheels as bearings, which allowed the pulley to work with great 



Fig. 23. — Mr A. Fraser using the Index Limnograpli, 



freedom. Some of the other instruments had rather broad bearings, and there was 

 considerable friction ; this was counteracted in practice by tapping the stand very 

 lightly with a pencil before taking the reading. If the bearings were made sharp 

 enough, however, the friction was so little that the tapping was unnecessary. In one 

 instrument, hurriedly constructed in the field, the bearings were simply a pair of brass 

 hinges, the ends of the axle resting in the nail holes. In this we could detect no 

 retardation whatever, due to friction ; the pulley appeared to turn as freely as on 

 friction wheels. 



