222 JtCCOUNT bJ" flOOkS. 



tube being then placed on two infulating fupports, and the 

 needle turned towards the part moll remote from the machine, 

 the tube was flightly inclined, in order that the oil might run 

 down to that part of its capacity which was neareft the prime 

 condudtor. He then put the machine in aflion, and with great 

 forprife obferved the oil gradually to enter into a ftate of ebul- 

 lition ; beginning at the furface and fpeedily acquiring a ftate 

 of eflfervefcence perfe6lly refembling that of fparkling Cham- 

 paigne. Upon opening the tube, a gas efcaped with violence, 

 which the author did not colled, but which well deferves to be 

 examined. This aftive electrician intends to fubjeCl the differ' 

 ent vegetable and mineral acids to the adion of eleClricity by 

 the fame procefs. 



Native Magnefia, 

 GIOBERT has found that a white earth conlidered as pure < 

 alumine and employed at Turin in the fabrication of porcelain, 

 contains 0,80 of magnefia. Van Mons. 



Gray^s Experl- Tlie Experienced Mill'ivright; or a Treatife on the ConJiru6tion of 

 cnced Mill- y?;;w<? of the mojl ufcful Machines, with the lateji Improvements, 



To which is prefixed a Jkort Account of the general Principles 

 of Mechanics and of the Mechanical Powers, lllujlratedwith 

 fortj/ Engravings. ^3/ Andrew Gray ^ Millwright, very large 

 quarto i 73 Pages of Letter Prefs, of the fame Size as the 

 Engravings, 



THE author is a pradical mechanic, who has been up«< 

 wards of forty years employed in ereding different kinds ol 

 machinery; and the greatefl part of the Defcriptions in thii 

 Work are of Machines which he has either planned or fuper^ 

 intended their conflru6tion. Thefe Drawings being accuratelj 

 made to fcale, are not, as he remarks, (o be confidered as me- 

 chanical fpeculations, always doubtful till fubjeded to aftuj 

 experiment, but as cafes of pradical knowledge, the effeds c 

 which have been fully tried and long approved ; moft of thet 

 being fliil employed for the purpofes of their original fabrications 

 . Previous to his Account of the Machines, this author give 

 a popular Treatife on Mechanics, in fix different chapters, bcii 

 ginning with General Principles and Definitions, which are fol 



lowec 



