4 1 8 Of Ike Propagation of Heat 



The bulb of the thermometer was of the same form 

 and size as in the instruments No. i and No. 2, that is 

 to say, it was globular, and half an inch in diameter ; 

 but the glass globe, in the center of which it was con- 

 fined, was much larger, being 3 inches y| lines in diam- 

 eter ; and the bore of the tube of the thermometer was 

 much finer, and consequently its length and the divis- 

 ions of its scale were greater. The divisions were 

 marked upon the tube with threads of silk of different 

 colours at every tenth degree, from o to 80, as in the 

 before-mentioned instruments. The tube or cylinder 

 belonging to the glass globe was 8 lines in diameter, a 

 little longer than the tube of the thermometer, and per- 

 fectly cylindrical from its upper end to its junction with 

 the globe, being without any choak ; the thermometer 

 being confined in the center of the globe by a different 

 contrivance, which was as follows. To the opening of 

 the cylinder was fitted a stopple of dry wood, covered 

 with a coating of hard varnish, through the centre or 

 axis of which passed the end of the tube of the ther- 

 mometer ; this stopple confined the tube in the axis of 

 the cylinder at its upper end. To confine it at its lower 

 end, there was fitted to it a small steel spring, a little 

 below the point o ; which, being fastened to the tube 

 of the thermometer, had three elastic points projecting 

 outwards, which, pressing against the inside of the 

 cylinder, confined the thermometer in its place. The 

 total length of this instrument, from the bottom of the 

 globe to the upper end of the cylinder, was 18 inches, 

 and the freezing point upon the thermometer fell about 

 3 inches above the bulb ; consequently this point lay 

 about i-J inch above the junction of the cylinder with 

 the globe, when the thermometer was confined in its 



