146 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



consists in compressing a limited volume of the gas, at the 

 pressure of the atmosphere, and determining its pressure im- 

 mediately after its reduction in volume. Much ingenuity 

 was manifested in managing the details of the process, so as 

 to conduce to successful and accurate results ; and the final 

 number for the ratio 434 differs scarcely at all from that 

 ordinarily accepted. 4 D, 1874, VII, 227. 



THE MECHANICAL EQUIVALENT OF HEAT. 



Fatigati has recently published a new determination of the 

 mechanical equivalent of heat, by means of the relation which 

 exists between the work expended to turn the disk of a Rams- 

 den electrical machine and the electrostatic decomposition 

 produced. To turn the disk of the machine and measure the 

 work, he winds two strings around the handle, each passing 

 over a pulley and carrying a weight at its extremity. He 

 deduces from the calculated work of the falling weights, after 

 subtracting the work consumed by friction and the work re- 

 tained by the weights, the resulting amount of force convert- 

 ed into electricity and heat. This heat is developed by cush- 

 ions, and is measured by a good mercurial thermometer and 

 a thermo-electro pile ; and the resulting equivalent in work 

 is subtracted from the preceding calculation. Finally, the- 

 amount of electrolization is measured by means of two test 

 tubes immersed in a large receiver containing acidulated wa- 

 ter. The mean result of twenty-eight determinations made 

 by Fatigati gives, for the mechanical equivalent of heat, 

 460.40 units of work. 7 A, XL VII., 155. 



A NEW CONTACT THEORY OF THE GALVANIC CELL. 



The well-known electrician, J. H. Fleming, has exhibited to 

 the Physical Society of London a new galvanic battery, con- 

 sisting; of three test tubes of dilute nitric acid alternated with 

 the same number of tubes of sodium-penta-sulphide ; ordinary 

 well-insulated bent strips, of alternated lead and copper, con- 

 nected together the neighboring tubes. By this device the 

 terminal poles are of the same metals all contact of dissimi- 

 lar metals being completely avoided. On connecting with a 

 coarse galvanometer the needle was violently and permanent- 

 ly deflected ; tested by the quadrant electrometer, the poten- 

 tial was shown to increase regularly with the number of cells. 



