162 PROCEEDINGS OF THE AMERICAN ACADEMY 



The Torsion System. 



The torsion wire was of such strength that one millimeter on the 

 scale at the edge of the wheel signified 11.8 grammes, or about T J^ of 

 the weights o p generally used. There were stops on the wheel, so 

 that it could not move through more than a small angle. The weights 

 were suspended by very flexible silk tapes, 6 mm or 8 mra broad and 

 0.3 mm - thick. They varied from 4.5 k - to 8.5 k - taken together. The 

 shaft, a b, was of uniform size throughout, so that the wire c sus- 

 pended the whole system, and no weight rested on the bearings. 



The pulleys, m, n, Fig. 6, were very exactly turned and balanced, 

 and the whole suspended system was so free as to vibrate for a con- 

 siderable time. However, as will be shown hereafter, its freedom is 

 of little consequence. 



The Water Jacket. 



Around the calorimeter, a water jacket, t u, was placed, so that 

 the radiation should be perfectly definite. During the preliminary 

 experiments a simple tin jacket was used, whose temperature w T as 

 determined by two thermometers, one above and the other below, 

 inserted in tubes attached to the jacket. 



The Driving Gear. 



The cog-wheels, g, h, were made by Messrs. Brown and Sharpe, of 

 Providence, and were so well cut that the motion transmitted to the 

 calorimeter must have been very uniform. 



The Chronograph. 



The cylinder of the chronograph was turned by a screw on the shaft 

 ef, and received one revolution for 102 of the paddles ; 155 revolutions 

 of the cylinder, or 15,810 of the paddles, could be recorded, though, 

 when necessary, the paper could be changed without stopping, and the 

 experiment thus continued without interruption. 



The Frame and Foundation. 



The frame was very massive and strong, so as to prevent oscillation; 

 and the whole instrument weighed about 500 pounds as nearly as 

 could be estimated. It was placed on a solid brick pier, with a firm 

 foundation in the ground. The trembling was barely perceptible to 

 the hand when running the fastest. 



