NEW HYDRAULIC ENGINE. 165 



feet of water in its defcent will raife three to the fame height 

 with well made pump work, with the velocity of one foot and 

 a half per fecond ; that is to fay, the prefent engine works ten 

 flrokes per minute, and this load is better or more productive, 

 than when either the velocity or the mafs are increafed. 



A much larger engine of the fame conflruction is at work at Account of a 

 Trenethick Wood Tin Mine in the parifh of Wendron, near e ^[?Sief r 

 Hailflone. It has a cylinder feventeen inches in diameter, 

 and works by a nine foot flroke, ten flrokes per minute. The 

 whole fall is thirteen fathom. It has been in conflant work 

 nearly three years night and day, with little or no repair, the 

 working parts being fo few and fimple. This engine muil 

 throw up about ten cubic feet per flroke, or 6000 feet per 

 hour, which is about 750 hogflieads. 



There is another new engine in the clifTat the Land's-End, 

 to clear the Riblows Tin Mine in the parifh of St. Jufl, which 

 is under the fea. Its cylinder is five inches in diameter, flroke 

 eight feet, and fall twenty fathom. 



Mr. Trevithack has erecled many fingle prefTure engines, Single prefTure 

 the conflruclion of which I hope hereafter to communicate to en S ines * 

 my readers. 



II. 



Experiments and Remarks on the Pajfage of Heat through Fluids 

 downwards, particidaiiy with Regard to the Uncertainty pro- 

 duced by the VeJJel ; with a Method of obviating that Uncertainty 

 altogether. % John Murray, M. D. Lecturer on Natu- 

 ral Philofophy and Chemifiry at Edinburgh. Communicated by 

 the Author. 



Edinburgh, Jan. 20, 1802. 



JL HE opinion which Count Rumford has advanced, that Count Rum- 

 fluids are non-condu&ors of caloric, may flill be confidered as ford's opinion 



J that fluids are 



admitting of difcuffion. Though fupported by a number of non-conduclors 



experiments contrived and executed with the greatefl inge- of neat is doubt- 

 nuity and addrefs, it is regarded by many chemifls as doubt- 

 ful, whether it is eflablifhed to the full extent that Count 

 Rumford has flated it, or whether the phenomena attending 

 change of temperature in fluids juflify more than the conclu- 

 sion, 



