Sirontian in Arragonite. '399 



the regulator, in order to observe them easier together; and 

 when they were thus situated, they agreed perfectly- The clock- 

 maker, with whom I was acquainted, communicated to me this 

 singular circumstance, and invited me to come to his shop to 

 witness it. 



We first remarked that the oscillations of the pendula were 

 in opposite directions ; they both receded from each other, and 

 both returned. Our first experiment was to give to their pen- 

 dula the same motion : then one relented, w'as a moment with- 

 out motion, and when it began to move, it was again in the 

 contrary way to the other, and continued so; their contrary 

 motions being isochronous. We were long without making any 

 surmise on the cause of this singular agreement, when at last we 

 took notice that both clocks stood on a floor, the boards of 

 which were elastic ; when therefore the pendulum, which was 

 very heavy, was moving on one side, its weight occasioned a 

 flexion of the board one way, which was restored when it moved 

 on the other side, and this effect surmounted the power of the 

 escapement. Having suspected that cause, we placed on the 

 boards some heavy weights to render them immoveable, and the 

 r"!ffect ceased on the clocks, each going at its proper rate. 



I presume that this might have been the case with Mr. Reid's 

 two clocks. 



I am, sir. 



Your obedient servant, 



J, A. De Luc. 



STRONTIAN IN ARRAGONITE. 



M. Laugier-the French mineralogist has published the fol- 

 lov.'ing interesting notice on this subject in the Memoires dii 

 Museum d' Hist. ISfat. V An. or 1 1"^ des Anvales. 



" Since Professor Haiiy observed that carbonate of lime pro- 

 perly so called, and arragonite crystallize very differently; it has 

 been suspected that these substances differ also in their compo- 

 sition, and many chemists have engaged in their comparative 

 analysis. The greatest number, however, concluded from their 

 experiments, that these two substances exhibit no difference in 

 chemical analysis,, and tl)at they contain exactly the same quan- 

 tities of lime, carbonic acid, and water. Of all the chemists 

 who have operated on these minerals. Professor Stromayer has 

 been the most successful. In May 1S13 he addressed a letter 

 to M. Haiiy, describing the process by means of which he dis- 

 covered the existence of strontian in arragonite, and separated 

 it from the carbonate of lime which constitutes about 97 per 



B I) 3 cent. 



