ELECTRICITY, MAGNETISM, AWD GRAVITATION. 83 



nearer together, and whilst the specific gravity is being in- 

 creased. This experiment was devised after the manner 

 of the condensation of atmospheric air by means of a syringe 

 constructed of glass, in which light is produced, and heat 

 sufficient to inflame tinder submitted to its operation, upon 

 the sudden and forcible depression of the piston. 



Exp, 4. — For this purpose a strong iron cylinder was em- 

 ployed, bored to the depth of one inch. Into the bore oi 

 the cylinder was fitted with tolerable accuracy an iron pis- 

 ton or plug, constructed for the purpose of ramming down 

 and compressing the potassium. A second smaller hole 

 was also drilled partly thiough the side of the cylinder, for 

 the insertion of the small bulb of a thermometer. A por- 

 tion of potassium was introduced — the piston was insert- 

 ed — the apparatus was placed between the extremities of an 

 ordinary vice — and when the thermometer was inserted, and 

 its indications noted down, a considerable compressive force 

 was applied to the extremity of the piston and cylinder. 

 The thermometer ascended in one instance from 53° to 55°, 

 and afterwards by increasing the compression 55| was ob- 

 tained. But in most instances not more than ^^ to |° could 

 be obtained with violent compression. By hammering also, 

 the thermometer indicated an increase of heat given off from 

 55** to 57^°j or 2^** of Fahrenheit ; but afterwards this quan- 

 tity could not be increased by very powerful percussion. 



Exp. 5. — h. strip of pasteboard was now wrapped round 

 the upper part of a new cylinder, and being somewhat ele- 

 vated above the upper surface of the latter, formed a trough 

 for the reception of mercury surrounding the piston, which 

 would, by the introduction of a thermometer, serve to show 

 the amount of heat given off by the sides of the piston during 

 compression. The apparatus being arranged, the thermo- 

 meter indicated 63|\ On compression by means of a screw, 

 the thermometel- gave 64% and a second compression 65° ; 

 the screw giving way, compression was carried no further. 



