TOR 



720 



TOR 



to roast. The Torrid Zone is that broad 

 belt of the earth included between the 

 tropics about 23 28' on each side of the 

 equator, called also the Tropical Zone. 



TOR'SION, from torqueo, to twist. The 

 force of torsion is the term used by 

 Coulomb to denote the effort made by a 

 wire or thread which has been twisted, 

 to untwist itself. On this principle Cou- 

 lomb constructed his torsion-balance, of 

 which, the torsion-electrometer, and the 

 torsion-galvanometer of Dr. Ititchie, are 

 merely modifications, for particular pur- 

 poses. 



(1.) TOR'SION-BAL'ANCE. This consists of 

 a stand T supporting a hollow vertical 

 rod, ST, which, in the balance of Coulomb, 

 was of pewter, that all magnetic and 

 electric influence might be avoided. On 

 this rod there are two sliding-pieces, CA, 

 and SP ; the lower of which carries a 

 plate A with a circle, divided like a dial- 

 plate, upon it; and the upper a piece P, 

 to which the torsion wire or thread is to 

 be fixed: N is a small bar-piece, with a 

 screw which clips the extremity of the 

 irire whose torsion is to be experimented 

 en, to which a weight, or an index, or 



lit 



TORSION-BALANCE. 



both, may be attached. The following 

 are the results : 1. The wire, being 

 loaded with different weights, did not 

 rest in the same position of the index, 

 but in a different position, with every 

 different weight. 2. The oscillations of 

 the index were isochronous, whether the 

 deflection was great or small. 



(2.) TOR'SION-ELECTROM'ETER, or Etsc- 

 TRIC-BALANCE. This consists of a thread, 

 o 6, of silk or spun glass, from which a 

 needle of shell-lac, c, is suspended. It Is 

 attached to a screw 6, by which it can b 



twisted rcnud it* axis, 

 carries a gilt ball 

 of pith, or a disc of 

 paper, at one ex- 

 tremity, which is 

 balanced by a coun- 

 terpoise at the 

 other; d is a me- 

 tallic wire, passing 

 through the glass- 

 shade, and termi- 

 nated by a metallic 

 ball at each end. 

 The ball of the 

 needle, and the in- 

 terior brass ball 

 of the wire, are 

 brought into con- 

 tact by turning the 

 screw 6, and the 

 index then pointa 

 to p on the scale, 

 which is marked 

 upon the circum- 

 ference of the 

 glass. 



(3.)TOR'STON-GAL- 



rANOM'ETER. n * is 



.he lower needle, 

 surrounded by a 

 coil of wire, and 

 connected with the 

 upper needle NS by a piece of strav 



TOMION-OAiVAKOMITBH. 



rh'.ch passes through the tipper pan oi 



