350 Scietttijic Newt, Accounts of Boohf ijfe, 



in North's apparatus, but with more water way; and this advantage I find in praiHiIce to- 

 be fuperiiir both in efFe£t and cheapnefs to die ingenious tube of fafety of Walter. That 

 contrivance, fo familiar to chemifts, confifts of a perpendicular tube with a fmall bafon at 

 top, and another refervoir or fwell at bottom, in an afcending part of the fame tube ; and 

 its a£tion when duly charged with mercury is, i. When the internal preflure increafes, the 

 mercury rifes, till the whole column is fupported, after which, upon any farther increafe, 

 the intire mafs of mercury is fuddenly blown into the upper refervoir, and gas is at once 

 let out, till the fpring is reduced nearly to that of the atmofpherej and 2. If there be ab- 

 forption, the external air in all cafes is very little refifted, but is fuffered to enter the 

 veflels. 



In my apparatus the preflure during the tranfmifilon of elaftic fluid through the valve is 

 cpnftant ; being equal to the re-a£lion of the liquids in the veflels C and D, and whatever 

 other external force may be added by the well known means : and whenever by diminu- 

 tion of the fire, or other caufes, the fpring of the gafes in B fiiall become lefs than the 

 preflure of rhe external air, that fpace will become partly vacuous ; but the valve will pre- 

 vent any return of the fluid from C, fo that the only effeft will be, that the materials ia 

 A will give out their produft fomewhatmore rapidly from the diminlflied re-aftion. 



A. S. B. 



SCIENTIFIC NEWS, ACCOUNTS OF BOOKS, S(c. 

 Dijccvery of Comets. 



AN the journal of the 8th of prairial the Notary Caigne announced, that he had 600 

 ft. to pay to any one who fliould difcover a comet. On the morning of the 23d of Mef- 

 fidor, C. Pons, keeper of the obfervatory at Marfeilles, difcovered one, which tlu-ee able 

 aftronomers of Paris alfo obferved the fame evening. The board of longitude, being re- 

 queflied to adjudge the prize, confidered C. Pons as having a degree of priority, to whicR 

 the three aftronomers of Paris aflfented, and the prize was awarded to him. I am folicit- 

 ing the government to offer a fimilar prize, to accelerate the progrefs of our knowledge of 

 cometsj the only branch of aftronomy which is not in an advanced fl:ate. It is fo eafjr, 

 however, to find comets, that any one, without being an aftronomer, may difcover them 

 when he pleafes. 



LALANDE. 



Memo'ires d? Agriculture, iifc. Memoirs of Agriculture, and Rural and Demefic Economy, 

 publijhed by the Agricultural Society of the Department of the Seine, and printed by Order of 

 the PrefeSl of the Departments Vol, I. Paris, 8vo. 447 p. i Plate. Price 4 fr. 



At 



