206 Baron Fourier's Historical Notice 



the first rank of European artists. Among the great number 

 of experiments which have served to direct his researches, we 

 may mention those which have estabhshed the mutual action 

 of two pendukims attached to the same support.* Each of 

 these instruments has its own proper motion, and if they are 

 placed in separate places, they will assume nearly the same 

 motion, because they are supposed to be regulated with great 

 care. Sometimes, however, we observe in them continual dif- 

 ferences, arising from the inevitable imperfection of workman- 

 ship. But if we attach them to two different points of a com- 

 mon support fixed in a wall, all their variations disappear ; — 

 the two pendulums assume insensibly the same motion ; — they 

 soon agree with each other with the most rigorous precision, 

 and will always preserve this common motion. 



This communication of two oscillatory motions had been long 

 ago observed in France -|* and England. M. Breguet has made 

 numerous and accurate experiments on this point, and they have 

 led him to construct double pendulums, the two parts of which 

 perpetually agree. They compose an unique instrument, the 

 going of which being more constant and better regulated, resists 

 the more all external agitations and accidental irregularities. He 

 has constructed, on the same principle, double chronometers, 

 which have the same property. 



' The reciprocal action of two parts of an apparatus suspended 

 on the same support, and sufficiently remote from each other, is 

 not the effect of the ambient air, as we might be led to believe 

 from the acoustic experiments of Sauveur. The principle of 

 this influence resides in the mass of the support, and it is from 

 the same cause that the vibrations of sonorous bodies are com- 

 municated to the hardest substances; — they penetrate the most 

 solid bodies, and rapidly agitate all their parts. Within the 

 sphere in which musical sounds are heard, the most compact 

 masses become sonorous ; — they resound in all their depth, and 

 they repeat the regular and symmetrical vibrations of the parti- 

 cles of the air. 



• See the article Horology in the Edinburgh Encyclopcedia, vol. xi. 

 p. 162, for some interesting details on this subject. — Ed. 



f We believe that it was first observed by our countryman, Mr John 

 EUicott. — Edin. Encycl. loc. cit. — Ed. 



