Philofopkical News, ipaj 



renders them lefs v'lfible. Ladly, it is poffible by this lamination, to incrcafe the fize of 

 a glafs when it is of fufRcient thicknefs. 



Cit. Pajot has not made public the procefs he has followed in his operations *. 



Bulletin des Science, Brumaire, An, 8. 



Simple Ji^ethod of obviating the Reft/lance of the Air again/} the Pendulums of Clocks. 



The celebrated David Rittenhoufe, late prefident of the American Philofophical Society, 

 has, in the fourth volume of their tranfadtions, defcribed a fimple method of removing the 

 effects of the refiftance of the air upon the ifochronifm of pendulums. He remarks, that 

 clocks of this con(lru6lion have been made to meafure time with aftonifliing accuracy ; and 

 if there be ftill fome caufes of inequality in their motions, the united efforts of mechanifm, 

 philofophy, and mathematics, will probably in time remove them. That the laft and leaft 

 of thefe caufes which perhaps may be worthy of notice, when all others of more importance 

 are removed, is that arifing from unequal denfity of the air, which, by varying the a£lual 

 weight of the pendulum, muft; accelerate or retard its motion. The extreme difference he 

 cftimates at half a fecond a day. He obferves, that a remedy dependant on the barometer 

 will not be ftriftly accurate, as the weight of the entire column does not precifely correfpond 

 with the denfity of its bafe. The Cmple method he propofes is as follows : 



The pendulum confifts of an inflexible rod, carrying the ball beneath and continued 

 above the centre of fufpenfion to an equal (or an unequal) diftance upwards. At this ex- 

 tremity is fixed another ball of the fame dimenfions (or greater or lefs, according as the con- 

 tinuation is fliorter or longer) but made as light as pofTible. Tiie ofcillations of this upper 

 ball will be accelerated by its buoyancy by the fame quantity as thofe of the lower would be 

 retarded, and thus, by a proper adjuftment, the two efFeds might be made to balance and 

 correct each other. 



Mr. Rittenhoufe, with his ufual candour, obferves, that he has no doubt but that, not- 

 withllanding the plaufibility of this theory, there will be fome difliculties in the pradtice. 

 But he is perfuaded they will not prove infuperable 



* Cit. Swediaurhas informed the fociety that a citizen, of the name of Hollemvegar, had made about i» 

 or 14. years before, in the prefence of Lavoifier, Meunier, and hinifelf, fojiie experiments, by means of which 

 he foldered together, in a firm and alnioft imperceptible manner, fome fragments of call glafs. 



Cit. Chaptal alfo obferves, that more than 1 5 years ago, a decanter of cryftai glafs was prefented to him, 

 the ftopper of which was fo perfeftly united with the neck, that it might be cut into plates, without the line 

 or circle of union being fenfibly perceived. The fluid it contained was the liquor /ilicum, and the decanter 

 bad remained reverfed for a confiderable time: 



From this fail he conceived the poflibility of foldering together two plates of glafs, and he offered my ideas 

 on this fubjeft, and fliewed the decanter to the audience in a public lefture, and I think by gradually abftraft- 

 ingthedifTolving alkali, it might perhaps be poffible to unite plates of glafs by the precipitated Ijlex. Note 

 OF THE Editor. 



I have lately feen fome pieces of glafs, of different colours, connefled or foldered together in plates by an 

 artift in London. The junflures were exceffively neat, Ibme of them in rjght lines, and fome waved ; fi-om 

 which lalt fa£l I conclude that the cement was capable of fupporting ignition and bending of the glafs. --- W.N. 



The 



