]3g COMPENSATION CURB FOR TIME-PIECES. 



weighed 100 grains, I put it into a cruciljle in the midst of 

 powdered charcoal, and exposed it for an hour to the most 

 violent forge fire. The gray mass I obtained weighed ex- 

 actly 32 grains less than the acid employed. 

 MolyWic acid Thus we may admit, without being far from the truth, 

 er's of mtar *^^* ^ hundred parts of rpetalllc molybdena absorb forty. 

 ami 32 5 of nine or fifty parts of oxigen, when this metal passes to the 

 cxigea, gp-^ state, and that consequently a hundred parts of molyb^ 



die acid contain thirty-two or thirty-three of oxigen. 

 Thii? confirms These experiments on molybdena in the metallic state, 

 of*the*sul?h'u''*^"^ **" molybdic acid, confirm the proportions I have as- 

 ret, signed to the constituent parts of the natiye sulphuret of 



molybdena. 



fTo be continued. J 



XI. 



C'onstructio7i of a Curl) affording a Compensation for the 

 Effects of Heat and Cold in Time-pieces. By Mr. Wil- 

 liam Hardy, No. 9.9, Cold-bath Square. 



Compensation J|. N PI. IV, fig. 2, the circles AB denote an expansion 

 cur escu e ■ ^j^^^^ composed externally of brass and internally of steel; 

 in consequence of which its curvature will be diminished by 

 Manner in heat, and increased by cold. The end A is fixed, and the 

 which it acts, j-g^t of the bar is at liberty, whence the ejftremity B will be 

 affected by a luotioo from temperature, which will carry the 

 pin F {between which and G the spring D E passes) a litr 

 tie onwards when the temperature rises, and a little back- 

 wards when it falls. But F will be scarcely at all affected 

 in the direction of the radius, because the tv/o semicircular 

 parts of the bar counteract eac|i other, C G is an arm of 

 brass fixed to the expansion bar, in the middle of its length. 

 It carries a pin G opposite to F; and as C is thrown inward^ 

 by increase of temperature through a space, amounting tp 

 the whole change to which the diameter of the curved ex- 

 pansion bar is liable, G will be carried towards F, and will 

 The balance allow the spring less play ; and by that means add to it? 



stiffness. 



