( 191 ) 

 MISCELLANEOUS INTELLIGENCE. 



§ I. Mechanical Science. 



1. Transparent Watch. — ^A watch has been presented to the 

 Academy of Sciences of Paris constructed of very peculiar mate- 

 rials, the parts being principally formed of rock crystal. It was 

 made by M. Rebellier, and is small in size. The internal works 

 are all visible ; the two teethed wheels, which carry the hands, 

 are rock crystal; the other wheels are of metal, to prevent acci- 

 dents from the breaking of the spring. All the screws are fixed 

 in crystals, and all the axes turn in rubies. The escapement is 

 of sapphire, the balance-wheel of rock crystal, and its spring of 

 gold. The regularity of this watch, as a time-keeper, is attri- 

 buted by the maker to the feeble expansion of the rock crystal in 

 the balance-wheel, &c. The execution of the whole shews to what 

 a state of perfection the art of cutting precious stones has been 

 carried in modern times. — Revue Ency., xliv. 796. 



2. On the Elastic Force of Vapour at high Temperatures. — A 

 committee, appointed by the Academy of Sciences, has been en- 

 gaged in carrying on experiments to determine the elastic force of 

 vapour at high pressures : the labours have principally devolved 

 upon MM. Dulong and Arago. The results have been obtained 

 experimentally up to 25 atmospheres, and extended to 50 by cal- 

 culations. That no error dependent upon the use of valves should 

 interfere, it was resolved to estimate the force exerted by the 

 columns of mercury sustained. A glass tube was therefore pre- 

 pared by MM. Thibaudeau andBontemps, consisting of 13 pieces, 

 2 metres (78.74 inches) each in length, 5 millimetres (0.2 of inch) in 

 diameter, and the same in thickness. Each piece was sustained by 

 counterpoises, so that the lower should not be crushed by the 

 upper, and the whole was erected in a square tower, which is the 

 only remains of the ancient church of St. Genevieve. 



Fearing that if the steam from a boiler were made to act di- 

 rectly upon such a column of mercury as this tube would sustain, 

 it might, from intermission of its force, occasionally produce such 

 sudden agitation in the metal as to endanger the safety of the 

 whole, it was resolved to form a kind of manometer, in which the 

 compression of a given volume of air should be ascertained, first, 

 by the column of mercury, and afterwards used as a measurer of 

 the elasticity of vapour at various temperatures. In this way the 

 estimations would be as accurate as if made directly by the column 

 of mercury. The preparation of this instrument gave an oppor- 

 tunity of examining the law of Mariotti, namely, that all gases 

 are compressed in volume in proportion to the energy of the 



