166 Prof. Potter on the Relations of the Elastic Force, 



A is the strong spherical boiler or receiver, about 5 \ inches 

 diameter. 



BC is a portion of the vertical glass tube with its wooden 

 scale ; the tube was rather more than 65 inches long, so that a 

 pressure of more than 60 inches of mercury, or more than two 

 additional atmospheres, could be employed. 



D is the ivory scale of the thermometer which has its elon- 

 gated bulb inside the receiver. 



E is the ivory scale of the thermometer which has its bulb of 

 an inverted pear shape, inside the chamber a. 



F is the microscope by which the motion of the mercury in 

 the stem of the exterior thermometer E is noted. There were 

 means of adjustment not drawn in the figure ; the magnifying 

 power used was 18 to 20 times linear. 



The chamber a was constructed of a piece of brass tube, having 

 in its interior a coil of six folds of the finest woollen fabric, and 

 inside this woollen coil was a cylinder of the best gilt paper. The 

 diameter of this cylinder of gilt paper was larger than the thickest 

 part of the pear-shaped thermometer bulb by about '04 inch, so 

 that there was abundant space for the escape of the jet of air all 

 around the bulb. A small quantity of wool was also wrapped 

 round the stem above the thermometer bulb to check the re-entry 

 of the external air, but not to affect the state of pressure. The 

 thermometer scale was fixed by wooden wedges inside the brass 

 tube, which had open spaces round the thermometer stem to 

 allow the free escape of the jet. 



The adapter b was a ring of box-wood fitting tightly on the 

 end of the nozle c, and receiving tightly the cylinder a, but 

 keeping them from contact. 



The nozle c was a piece of brass, cylindrical outside, but with 

 a milled ring for screwing it to the end of the pipe of the stop- 

 cock. The aperture of the nozle was about T ^th of an inch. 

 It was made by passing a fine needle through the brass, when 

 the drill by which the pipe was formed was just about to come 

 through the end of the brass ; the aperture was then carefully 

 finished so as to have a sharp edge. The end of the nozle was 

 covered, except a small space over the aperture, with two folds 

 of woollen cloth and a disc of gilt paper cemented in their place. 



The condensation was performed with a condensing syringe 

 screwing to the pipe with the stopcock. 



The sphere A, containing about 90 cubic inches, was easily 

 injected to a density of three atmospheres in one minute of time. 

 The temperature inside rose by this 4° to 6° Fahrenheit, accord- 

 ing to the friction of the piston and consequent heating of the 

 condensing syringe, and was allowed half an hour or more before 

 it was used, in order that the whole apparatus might acquire a 



