i^40 



Time of high- 

 water at Breft 

 has n«t varied in 



NATIVE CARBONATE OF MAGNESIA. 



phenomena of the tides to vary. A comparifon of the obfer- 

 vations made at Breft, has made known to Cit. Laplace, that 

 circumftances tliere increafe the adion of the moon one-fixth ; 

 and with this modification the refult of the theory is a mean be- 

 tween thofe given by obfervation. 



The high tide of the 15th of September 17 15, in the morr^- 

 ing, and that of the 23d of March laft, in the evening, were 



near a century, nearly equidiftant from the fyzygy, which fliould give the fame 

 hour for the tides, if the local circumftances of the harbour have 

 not varied in the interval of nearly a century. The firft was 

 obferved at half after four in the morning, true time; the 

 fecond, at 29 minutes after four in the evening : whence it 

 appears, that the time of the tides at Breft has not varied in that 

 period. 



Cit. Laplace has propofed to the firftclafsof the Inftitute, to 

 folicit government to direct a feries of obfervations to be made 

 on the lides in the different harbours of France; and to appoint 

 a committee to draw up a fingle body of inftrudions for the 

 beft mode of making thefe obfervations. Both propofals were 

 adopted. 



The whole of the paper, of which an abftrad is here given, 

 will be printed in the ConnoijJ'ance des Tans. 



Series of obfer 

 vations on the 

 tides propofed. 



Magnefia with 

 carbonate gene 

 rally in fmall 

 quantity in 

 ^ones. 



Charafters of 

 the ftone of 

 Caftclla Monte. 



VI. 



Abfiraci of a Paper by Cit. Guyton-Mouvkau, entitled an 

 Examination of a native Carbonate of Magnefia* . 



1 HOUGH magnefia is a conftitiient part of many flones, 

 it enters into them but in fmall quantity, with few exceptions. 

 Native carbonate of magnefia occurs ftill more rarely in any 

 confiderable proportion. Citizen Guyton, however, fearch- 

 ing for a clay poffefted of the hygrometric property in the 

 higheft degree, lately found a very large proportion of native 

 carbonate of magnefia in a ftone in the vicinity of Caftefla- 

 Monte, which is there confidered as a clay very rich in 

 alumine. 



This ftone is as compact as the hardeft chalk, in an amor- 

 phous mafs, and as white as cerufe. It does not fenfibly ad- 

 here to the tongue, and has no argillaceous fmell. Water a6ls 



* Bulletin des Sciences, No. 75. 



very 



