N THE MECHANICAL EQUIVALENT OF HEAT 



427 



up the water. Hence the paddles were made without solder, and were 

 screwed together. Indeed, there was no solder about the apparatus. 



But, for my purpose, the number of paddles must be multiplied, so 

 that there shall be no jerk in the motion, and that the resistance may 

 be great; they must be stronger, to resist the force from the engine, 

 and they must be light, so as not to add an uncertain quantity to the 

 calorific capacity. Besides this, the shape must be such as to cause 

 the whole of the water to run in a constant stream past the thermom- 

 eter, and to cause constant exchange between the water at the top and 

 at the bottom. 



FIG. 7. 



FIG. 8. 



Fig. 7 shows a section of the calorimeter, and Fig. 8 a perspective 

 view of the revolving paddles removed from the apparatus, and with the 

 exterior paddles removed from around it; which could not, however, be 

 accomplished physically without destroying them. 



To the axis cb, Fig. 7, which was of steel, and 6 mm. in diameter, a 

 copper cylinder, ad, was attached, by means of four stout wires at e, 

 and four more at f. To this cylinder four rings, g, Ji, i, j, were attached, 

 which supported the paddles. Each one had eight paddles, but each 

 ring was displaced through a small angle with reference to the one 

 below it, so that no one paildle came over another. This was to make 

 the resistance continuous, and not periodical. The lower row of pad- 

 dles were turned backwards, so that they had a tendency to throw the 

 water outwards and make the circulation, as I shall show afterwards. 



