76 Progress of Invention. 



gilt Laving been protected with varnish ; after which an amalgam 

 of gold is to be applied, and the mercury is to be evaporated by- 

 heat. Amalgam containing only the one two-hundredth part 

 sodium will be sufficiently active to amalgamate tarnished metals, 

 or iron and platinum, which, in ordinary circumstances, have no 

 tendency to become wetted with mercury. 



Improvement in Hoeological Machines. — It is scarcely too much 

 to assert that the rate of a well-constructed clock or watch would 

 be invariable, but for alterations of temperature. "With an increase 

 of temperature the pendulum is lengthened, and consequently its 

 vibration is rendered slower ; with a decrease, the contrary takes 

 place. Analogous effects are produced by changes of temperature 

 on watches and chronometers : and as, during summer and winter, 

 night and day, the temperature of the air is perpetually changing, 

 it may well be supposed that without the adoption of some means 

 for counteracting the effects of changes of temperature, the rate of 

 clocks, watches, and chronometers would be subject to perpetual 

 alteration ; and such is the case with ordinary horological instru- 

 ments. But ingenious means have been devised for compensating 

 the changes produced by temperature. These means, however, are 

 subject to two considerable drawbacks : they are more* or less 

 complicated and therefore expensive, and they are rarely as perfect 

 in their action as might reasonably be desired. A new mode 

 of compensation for clocks, watches, and chronometers has been 

 invented by M. Menon, which is extremely simple, and therefore 

 inexpensive ; and very effective, because calculated exactly to 

 counterbalance the effect of changes of temperature, by bringing 

 into opposite actions two precisely equal forces. In the compensa- 

 tions hitherto in use, the expansions and contractions of different 

 substances are made to counteract each other ; and thus, from the 

 difficulty of making them exactly equal in their operations, a serious 

 source of error is introduced. With the gridiron pendulum, for 

 example, the rods which raise the bob of the pendulum may 

 not expand to the same degree as the rods of a different metal which 

 lower it : and the raising and lowering may thus not be equal — that 

 is, the length of the pendulum may vary. With the mercurial 

 pendulum, the centre of gravity of the mercury may not be altered 

 in position so as exactly to counterbalance the alteration in the 

 length of the pendulum rod produced by change of temperature. 

 In M. Menon's contrivance, the two portions of the compensation 

 are exactly the same in every respect, and therefore when their 

 expansions or contractions are made to neutralize each other, 

 the effect must be zero — that is, the length of the pendulum must 

 remain unchanged. In the construction of a compensation pendu- 

 lum on this principle, two rods of the same metal, and of the same 

 dimensions, are used ; the pendulum is attached to one, and the 

 other is coiled up — merely for convenience, the alterations produced 

 by change of temperature being exactly the same whether the rod is 

 in the form of a right or curved line. The rod, in the form of a 

 spiral, is used to suspend the bob of the pendulum, or the pendulum 

 itself. For this purpose, one end of it is fixed to the bob, which 



