236 



Mr. J. Joly. 



the fixed upper part of the calorimeter. It is at a convenient slope 

 for reading', and its bulb penetrates into the calorimeter till just over 

 the substance placed on the carrier. In careful work it is well to 

 read the thermometer by a telescope. A very accurate, but less con- 

 venient, way is to read with a lens, which is moved about till the 

 image of the last graduation on the stem of the thermo neter reflected 

 in the thread of mercury is seen to be covered by the ga'a«duation. 

 There is then no parallax error. The thermometer is withdrawn just 

 before letting in steam, and the tubulure plugged with a small cork. 

 After the weighing is finished, a thermometer for reading the boiling 

 point may be inserted in this tubulure. Previous to the admission of 

 steam, the tubulure taking the steam-pipe is kept closed by the 

 stopper of wood overlaid with cloth, shown dotted in its position. 

 The side pieces which go towards supporting the table for the balance 

 are cut out as shown at each side, so that the operator can see to 

 remove the stopper, and insert the steam-pipe rapidly. My practice 

 is to pinch the rubber tube conveying the steam for the moment in 

 which the steam- pipe is being laid on; when in position it is released, 

 and steam let flow into the calorimeter. The steam-pipe is in part 

 covered with thick baize, so that it may while hot be grasped by the 

 hand. 



A section, fig. 2, PI. 6, full size, shows the arrangement adopted to 

 render the wire in its passage through the roof of the calorimeter 

 self-adjusting in the centre of the orifice provided for it, or rather to 

 render the orifice self-adjusting on the wire. The coned roof of the 

 inner wall of the calorimeter is carried through the external cylindrical 

 jacket, flanged at the top, and ground smooth. A loose coned piece 

 also with ground flange rests on this. The upper end of this cone is 

 turned down to a knife edge, and just brought flat on a fine stone. 

 On this a tiny disk of copper or brass drilled centrally with an orifice 

 about two-thirds of a millimetre in diameter is laid looosely. The 

 wire bearing the carrier is brought through this disk, which weighs 

 about 22 milligrams. Above the disk is placed a spiral of fine 

 platinum wire held in a forceps, which by two binding screws may be 

 put in circuit with a battery. Through this the wire also passes. 

 Finally, before the wire rises into the balance, it is embraced by an 

 inverted cone (fig. 1), turned in hard wood, which is adjustable in 

 position, being held to the under face of the table by two spring 

 clips, as a slip is held on the stage of a microscope. On the table a 

 balance, not shown in the figure, stands. The wire ascends to the 

 left arm of this balance. 



The adjustment of the suspending wire is very obvious. The 

 balance is set so that the wire hangs freely through a large aperture 

 in the table provided for it. The inverted cone and the small cone 

 on the calorimeter are next set to let the wire pass centrally. The 



