570 



smft as the wind would be a " slow coach," for the average 

 speed of several years is but ten miles an hour. That, how- 

 ever, gives 1500 revolutions per hour, and no support of the 

 lower pivot stood long; hard steel Avas replaced by stones. 

 He showed an agate cup which was actually di'illed after a year's 

 work, and a sapphire which failed after two. At last he sup- 

 ported it entirely above on five balls of bronze, which bear both 

 the vertical and lateral pressures. After a year's use they 

 showed no signs of wear (they must be oiled), and the friction 

 is but l-300th of the load, being but 53 grains, of which 21 be- 

 long to the mill and 32 to the clockwork used in recording the 

 observation. He described that clockwork. Two engraved 

 circular papers are made to revolve ; one by a direction vane, as 

 the wind veers, the other by the windmill, at such a rate, 

 that it turns one degree for every mile traversed by the wind, 

 or once for 52,800 revolutions of the miU. The necessary train 

 for this was aiTanged by one whose premature death is a 

 heavy loss to science, the late IVIr. Richard Sharpe. The time 

 is recorded on these papers by pencils moved by the clock at the 

 rate of six inches in twelve hours. That motion, combined 

 with the space rotation, traces on its paper a spiral, contrasting 

 most powerfully with the blurred and jagged stripes of pres- 

 sure gauges. The dhection-record is a sector shaded by the 

 pencil, whose breadth depends on the veering of the wind. 

 This, if exhibited in its fuU extent, would be very unsightly ; 

 and he described various contrivances to lessen it, in particu- 

 lar that used by the President, a supplemental Aviudmill, which 

 acted whenever the wind was oblique to the plane of its rota- 

 tion, and turned the whole instrument. Dr. Robinson's ar- 

 rangement is also very effective. In the first place the motion 

 is communicated from the vane to the paper by a long spiral 

 spring, in bending which many of the momentary changes are 

 entirely expended ; secondly, a large fan, hke that of a blow- 

 ing machrue, exposing about sixteen square feet, and very 

 light, is connected with it by a rapid speed. This moves with 



