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bo furnished with some sort of anemometer, and with some easy 

 means of eliminating the effect of the motion of the vessel, he began 

 to consider what would be the most appropriate form of anemo- 

 meter to be used at sea ; for several kinds had been already tried, 

 but had failed, as he thought, from not being constructed on a suit- 

 able principle. The species which the author considered the best, 

 was that which should imitate, as nearly as possible, mutatis mutandis, 

 the log-line by means of which the ship's way through the water 

 is determined; for that instrument seems to have preserved its 

 situation and supremacy over all others on board-ship amongst all 

 nations, and from the time of Columbus to the present, mainly on 

 account of the appropriateness of the principle involved. After 

 describing several means by which the principle might be imitated 

 to different degrees, the preference was given to Mr Edgeworth's 

 anemometer, in which a horizontal wheel, armed with hemispheres on 

 the end of each spoke, revolves in the saine direction, from whatever 

 quarter the wind may blow ; and the centre of each cup moves at 

 one-third the velocity of the current, by reason of the greater force 

 of the wind on the concave than on the convex side. A series of 

 experiments was entered on to determine the best shape and size to 

 give the machine in practice, and the result at length arrived at 

 was exhibited on the table, in the form of an anemometer with four 

 horizontally revolving arms, on the ends of which were hemispheres, 

 each four inches in diameter, with a radial distance of six inches. An 

 endless screw on the vertical axis of this revolving part gave motion 

 to a train of wheels which served to count the number of revolutions 

 made in a given time. A weight of 1-^ grains in the centre of one 

 of the cups, was found sufficient to overcome the resistance to 



motion. 



Some experiments were described which seemed to shew that the 

 instrument could be fully depended on, and that the stremjth or 

 velocity of the wind at sea might now be always entered in the log- 

 book, as being of so many knots per hour, instead of in the usual 

 unmeaning manner ; and as the vanes actually used in ships give the 

 direction of the wind with sufficient accuracy, all the elements neces- 

 sary for eliminating the effect of the motion of the ships, or for 

 deducing the true wind from the apparent one, may be assumed as 

 being attainable, but the description of the practical method proposed 

 for adoption was deferred for the next Meeting. 



