490 



Mr. H. Tomlinson. The Influence of 



From these relations we obtain — 



_^__=a constant, 



or that the cube of "Young's Modulus" varies as the seventh power 

 of the thermal capacity per unit volume. 



Description of Apparatus and Mode of Experimenting. 



Thermometers. — Three thermometers were employed; these were 

 made by Casella, and after having been filled were kept by myself for 

 a year; they were then sent back to the maker to be graduated, and 

 1 month afterwards their graduations were tested at Kew, and were 

 found to accord very accurately with the Kew standards throughout 

 the whole of their ranges, which were in the three instruments from 

 -5° C. to 30° 0., from 30° C. to 65° C, and from 65° C. to 105° C. 

 respectively. The graduations were made to one-tenth of a degree 

 centigrade, and were of such a length that it was easy to estimate to 

 one-hundredth of a degree. 



Calorimeter. — The calorimeter was of the well-known kind intro- 

 duced by Regnault, and the silver coatings of both the inner and 

 outer copper vessels of the instrument, which was new, were through- 

 out the experiments kept uniformly bright. The mass of the inner 

 vessel of the calorimeter was 133 grams, and the water equivalent of 

 it, the stirrer and thermometer, was determined from the mean of 

 several experiments made by introducing into the vessel known 

 masses of water at different temperatures to be 138 grams, whilst 

 the water equivalent, as calculated from the mass and thermal 

 capacity of the vessel stirrer and thermometer, was, on the assump- 

 tion of the heat being absorbed uniformly throughout the vessel,. 

 140 grams. The probable error of an observation of the thermal 

 capacity of a wire resulting from error in the determination of the 

 water equivalent would in no case exceed 0*06 per cent. 



Mode of Adjusting the Wires. 



The wires, which had been previously well annealed, were wound 

 round a steel rod, and so made into coils of length about 2 inches, 

 inner diameter j inch, and outer diameter 1 j inches ; the rod was 

 then withdrawn, and the coil inserted into a thin brass envelope. 

 The envelope (figs. 1, 2) consisted of a hollow cylinder AB, 2 inches 

 in length and 2 inches in diameter, terminated at both ends by a 

 truncated cone. The closed conical end BDB could be unscrewed so 

 as to receive the coil of wire, and was, after the insertion of the coil, 



force does vary inversely as the fifth power of the distance. According to M. Heen, 

 the force is inversely as the seventh power of the distance, but it would seem to 

 follow from Poisson's mathematics that the law should be really the one pre- 

 viously indicated. 



