ships' velocity. 343 



experiment, with the precaution of having my galvanic appa- 

 ratus in one room, and my wires, passing through two small 

 holes in a door to the distilled water, in an adjoining room. 

 I employed a similar power as in the former experiment, and 

 decomposed the same quantity : in this there were not the 

 slightest traces of muriatic acid. I am induced to think that 

 such has been the cause of Pacchioni's error. In a periodical Doubts and 

 work I noticed some experiments of Mr. Peel, of Cambridge. Ul^MrS?" 

 Mr. Peel says he discovered this acid after decomposing two experiments, 

 ounces of water. A thousand galvanic plates in troughs, if 

 even replenished every twenty-four hours with fresh acid and 

 water, would not effect the decomposition of so large a quan- 

 tity of water in three weeks. I wish the particulars of Mr. 

 Peel's experiments, as to the extent of his power, and the nature 

 ot the fluid he employs, had been described. 

 I am, dear Sir, 



Yours, respectfully, 



C. WILKINSON. 



X. 



Letter from H. Ha mill, jun. Esq. on the Measure of a 

 Skip's Velocity. 



Tu Mr. NICHOLSON. 

 SIR, 



H. 



A\'ING lately had occasion to look over the various 

 methods of ascertaining the distance run by a boat, particu- 

 larly in short distances, such as in surveying harbours, it 

 struck me that the following might answer the purpose. 



In the method proposed by M. Pitot, described in Gre- projjosed im- 



gory's Mechanics, vol. ii. page 414, two tubes are used, P^^^f,""^"*- '". 

 ^ ^ . . . Pitot's method 



one of which has at its lower extremity, a trumpet mouth, of measuring a 

 the other straight throughout. Now when the vessel makes ^^'P'^^ velocity, 

 way, in his method, her velocity is ascertained by the differ- 

 ence of height to which the water rises in each tube. But as 

 the velocity of a vessel, impelled by oars or sails, especially in 

 a sea not perfectly calm, cannot be perfectly uniform, the 



watct 



