48 Method tf meafuring a Ship's Way at Sea. 



the workmen} partly, I fuppofe, becaufe the pivots are afterwards more expeditloufly 

 finifhed, and partly becaufe a watch is thereby liable to be the fooner unferviceablc. 



There is, however, one recommendation more of a large contrate wheel, which I fhall 

 juft mention before I conclude the fubjeft: as the arbors of the contrate and balance wheels 

 of watches of a common conftruftion, placed one horizontally, and the other perpendicu- 

 larly, they are neceflarily laid at one fide of each other, fo as juft to efcape touching as 

 they crofs, by reafon of which pofition an obliquity is occafioned in the direftion of their 

 aflion, which is the greater the fmaller the contrate wheel is, and vice verfd ; and which 

 frequently occafions the flopping of the watch : an enlarged contrate wheel will confe- 

 quently greatly diminlfti this caufe of imperfedtion, and will therefore confticutc an addi- 

 tional improvement. 



lam, SIR, 



Your's refpeftfully, 



W. PEA^LSON. 

 Par fan's Green, April 13, i8oi. 



III. 



A Method of meafuring a Ship's Way at Sea, -with Obfervations on other Branches of the Art of 

 Navigation. By JfoBN CooKEy Efq. M. R. I. A, Communicated by the Author. 



\ j VT a tube with a few inches of one end bended to a right angle, be affixed to a (hip, in 

 fuch a manner that the longer part may enter through the (hip's bottom below the water 

 line, and be faftened in a pofition parallel to the maft, and fo that the recurved end {hall be 

 immerfed in the water in a pofition parallel to the keel, with its orifice pointed towards the 

 Ihip's head. Let the upright part of this tube be furniflied with a fmall fpouting aperture 

 within the fliip, at the level of the external water ; then fuppofe it to move fteadily through 

 fmooth water in the dire£tion of its length, the impulfe of the ftream on this orifice will 

 be as the fquare of the (hip's velocity (fee note A). And fince the column of water thrown 

 up in the ereft tube by this force muft be in equilibrio with it, the perpendicular height of 

 this column of water will be as the fquare of the (hip's velocity alfo ; in which cafe the 

 water will flow from the aperture into the (hip, while the vefTel moves forward, and the 

 quantity difcharged will be in a fubduplicate ratio of the perpendicular altitude of the 

 column in the ereft tube ; that is in the fimple ratio of the (liip's velocity. If therefore 

 the quantity difcharged through this aperture in paffingover a mile be obferved, the a£tual 

 diftance run at any time may be found, if the water ejedled be preferved and meafured (fee 

 note B). 



But the pitching of a velTel at fea, and the motion of lee way, would caufe the (Iream 

 to fall obliquely on the orifice, and confequently affed the preflure and alter the ratio 



which 



