6 IMPROVEMENTS IN HYDRAULIC ENGINES. 



propofes the very fame method of working the valves by a 

 tumbling weight, as that called the tumbling bob, in Mr. 

 T's defcription. In Belidor's engine the pifton cylinder and 

 pump are both horizontal, which is the molt material diffe- 

 rence, but the principle is entirely the fame as Mr. Trevi- 

 thack's. 



Mr. Belidor does not claim the honour of this invention, 

 but only propofes the engine I allude to, as an improvement 

 on one executed on the fame principle at Seve, between 

 Verfailles and Paris, in the year 1731, by Denifard and 

 Deuille, for which they obtained a patent from the king of 

 France for twenty-one years ; of which engine there is alio a 

 defcription in the fame chapter of the above work. 

 Propofa! of air I beg leave to fuggeft, that it might be a conliderable im- 

 pfftonT" ln thC P rovement to tnis engine to have its aftion made elaftic, by 

 the addition of an air chamber, on the fame principle as that 

 ufed in engines for extinguifhing conflagrations ; fuch a one, 

 feems to me, might be beft effected by making the pifton 

 hollow, and of a larger fize, to ferve for this purpofe, as the 

 air fpring would then act both on the upper and lower pref- 

 fure of the water ; Figure 3 is a fketch of this method, in 

 which A reprefents the hollow pifton. 



I hope the length of this paper will be excufed by the 

 circumftance of my not having received your Journal for 

 March till I had written the moft of it, and having had of 

 courfe, to add the remarks on the pifton preflure engine to 

 the reft. 



I am, SIR, &c, 



W. H. B. 



II. 



Remarks of the prefent State of Paper-making in England and 

 France*. By H. Campbell, M.D. Communicated by the 

 Author, March 26, 1802. 



Whether the ad- J[ HE additional duty on Paper has not been the chief caufe 

 :iona uty on ^ ^ e diminution ' m t ne book and paper trades of this country. 



paper nas pun- * ■* •> 



cipally injured After 



book trade. 



* The importance and authenticity of the chemical, mechanical, 

 and other facls ftated in this Memoir, and of the object itfelf in 



general 



