344 Hydraulic Engint.'—Oh/crvalions on Light and Heat, 



- The dotted lines reprefent apparatus for raifing water below the bottom of tube 2, to be 

 ufed inftead of thofe above the ciftern C. 



This arangement places the utility of the engine in a very ftriking point of view, particu- 

 larly when we wilh to employ a fmall ftream to operate upon machinery ; where the defcent 

 is great, but the quantity of water inadequate to the purpofe even with the alTiftance of a 

 refervoir. In this cafe let nearly the whole of the water defcend through the veflel B and 

 tube 2, before it enters the refervoir; and let the water after it has turned the wheel be 

 collected in a lower bafon. If the defcent from the higher refervoir be fo great as to allow 

 part of the lower body to be raifed into it again at once, the quantity raifed may be made 

 nearly equal to that which has defcended through the tube a ; if it can be done at twice, it 

 will be lefs than half that quantity. Still however I think ic will be very advantageous to 

 employ fuch a method, as the operation of the engine is conftant and diminilhes no power 

 of the machinery *. 



In fituations where this machine can be eredled it may be of confiderable ufe, for raiCng 

 water out of mines, for draining pieces of ground, or elevating the water employed in do- 

 meftic purpofes. 



I am Sir, 



Your humble Servant, 

 Sept. 1 6, i8oo. L. 



III. 



Obfervations and Experiments on Light and Heat, with fome Remarks on the Enquii ies of 

 Dr. Herfchel, refpeSing thofe ObjeBs, In a Letter from, Mr. John Leslie. 



To Mr. NICHOLSON. 

 SIR, 



London, 05t. 9, 1 8co. 



I 



AM induced to trouble you with this communication in confequence of the account inferted 

 in your laft number, of two papers lately read at the royal fociety* Aware that the celebrity 

 which their author has fo juftly acquired as a (kilful and indefatigable obferver will, from the 

 indolence of our habits, confer a certain extrinfic weight, even when he embarks in philo- 

 fophical fpeculation, — I cannot help feeling, anxious, left that authority (hould in the pre- 

 fent inftance retard the progrefs of fcience by giving currency to opinions which, I am fully 

 convinced, are inacurate or unfounded. It is not my intention to cenfure the efforts of 

 genius i but I would fuggeft how liable are men of talents to commit miftakes in matters 



* The leafoning in this paragraph appears to be defeftive, becaufe the machine engages part of the fall, 

 and thus diminilhes the effeft more than the raifed water can augment it, N. 



•. . of 



