ADDENDUM TO PAPER ON WIND PRESSURE. 
741 
3.— ADDENDUM TO PAPER ON WIND PRESSURE IN YOL. Y. 
OF AUST. ASSOC. ADY. SCIENCE, r. 573. 
By Professor W. C. KERNOT , M.A., C,E., F.R.G.S. 
In my previous paper on wind pressure certain important points 
were left to some extent in doubt, my methods of experimenting not 
being sufficiently perfected to give thoroughly reliable results. 
During the past year I have succeeded in constructing improved 
apparatus, and obtaining therewith results that I consider satisfactory. 
The first point left in doubt was the relation between velocity 
and pressure. The general formula is — 
P=<? Y\ 
But considerable difference of opinion existed as to the values of c 
and n. Taking P as pounds per square foot, and V in miles per 
hour, values of c had been given varying from *0035 to '007, '005 
being that generally adopted on the authority of Smeaton, and n was 
generally on the authority of Newton, confirmed by the experiments 
of Rouse, taken as 2 ; while Crosby, aided by most costly and 
elaborate apparatus, maintained stoutly that it was unity. (See 
Engineering, 13th June, 1890, p. 716.) 
In my previous paper experiments are described made with a 
blowing machine and an Osier anemometer, and also with an Osier 
anemometer carried on a bicycle. The former of these were unsatis- 
factory owing to the difficulty in measuring the exact velocity of the air, 
and the latter owing to the speed being simply estimated, not accurately 
measured, and the experiment being made out of doors, where the 
atmosphere itself was always to a greater or less extent in motion. 
The recent experiments were made with a whirling machine, in 
some respects an improvement upon that used by Crosby. It consisted 
of a strong radial arm, fixed to one end of the crank shaft of the gas 
engine at the engineering laboratory at the Melbourne University. 
Along this arm ran an axis, suspended between centres, so as to move 
with as little friction as possible. At the outer end of this axis a 
lever was attached, parallel to the shaft of the engine, carrying a piece 
of stout cardboard 8 inches by 4J inches, or exactly one-quarter square 
foot area, the pressure again A which was measured. At the inner end 
of the axis a second and much shorter lever was attached, at right 
angles to the first, the free end of which was exactly in the centre line 
of the crank shaft of the engine. To this was attached, by a ball and 
socket swivel joint, a wire leading to a delicate and carefully calibrated 
spring balance, by which the pressure on the card was measured. Thus 
the pressure could be read at any moment without stopping the engine, 
as was necessary with Crosby’s apparatus, illustrated in Engineering 
of 13th June, 1890, p. 718. 
With this apparatus twenty-three experiments were made, with 
linear velocities of from twelve to twenty-seven miles per hour, as 
per table below : — 
No. of experiment. 
Velocity in miles per hour. 
Press ure in lb. per s ft. 
1 
12 
•29 
2 
12 
•47 
3 
12 
*56 
4 
12*8 
*65 
2 z 
