Mr. smeaton on Mechanic Power . 455 
a courfe of experiments upon this fubjed. Thefe expe- 
riments, with the conclulions drawn from them, have 
already been communicated to this Society, who printed 
them in vol. li. ot their Tranfa£tions for the year 1759, 
^■fid. for this communication I had the honour ot receiving 
the annual medal of Sir Godfrey copley, from the 
hands ot our very worthy Prefident the late Earl of 
MACCLESFIELD. Thofe experiments and conclufions 
hand uncontroverted, fo far as I know, to this day; and 
having tlnee that time been concerned in directing the 
conftru6tion ot a great number of mills, which were all 
executed upon the principles deduced from them, I have 
by that means had many opportunities of comparing the 
eflecfts actually produced with the effects which might 
be expected from the calculation; and the agreement, 
I have always found between thefe two, appears to 
me fully to eftablifh the truth of the principles upon 
fliot to an underfhot, fays, Annotat. on lefture 12. vol. II. p. 532. that from 
his own experience, £ ‘ a well-made overfhot mill ground as much corn in the 
“ fame time with ten times Iefs water;” fo that betwixt belidor and desa- 
culiers here is a difference of no lefs than 60 to 1. 
Again, belidor, vol. II. p. 72. fays, that the center of gravity of each fail 
of a wind-mill fliould travel in its own circle with one-third of the velocity of 
the wind ; fo that, taking the diftance of this center of gravity from the center 
of motion at 20 feet, as he Hates* it p. 38. art. 849. the circumference will be 
exceeding 126 feet.Englifh meafure : a wind, therefore, to make the mill go 
twenty turns per minute, which they frequently do with a frefh wdnd and all-' 
tlieir cloth fpread, would require the wind to move above eighty miles an hour ; 
a velocity perhaps hardly equalled in the greateR florins we experience in this 
climate. 
which 
