358 
Proceedings of the Royal Society of Edinburgh. [Sess. 
means that for no load the plate deflects this amount. It must be assumed 
that the plate is in a somewhat unstable state, similar to that of a wire 
which is being tested by direct loading for Young’s modulus. The plate’s 
initial irregular curvature corresponds to the slight and perhaps imper- 
ceptible kinks in the wire, which require a very small force for their 
removal, after which the wire follows the elastic law. The dotted portion 
of the line near the origin gives the hypothetical deflection there, and the 
straight line is made up by joining up the points that commence some 
slight distance away. It appears, then, that for little or no load the plate 
deflects at the centre an amount '005 in. before it begins to follow the 
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elastic law, so that this quantity must be subtracted from the actual 
reading. When this is done at the centre and corresponding amounts at 
points along the diameter right up to the circumference, a curve is obtained 
for deflection that is almost indistinguishable from that obtained from the 
equation. 
Plate B. Load 20 lbs. per sq. in. 
At centre, theoretical value of deflection = *0337 in. 
„ experimental „ „ = -039 — '005 = -034 in. 
Plate C. Load 15 lbs. per sq. in. 
At centre, theoretical value of deflection = -0417 in. 
„ experimental ,, „ = 054 — 012 = '042 in. 
Plate D. Load 20 lbs. per sq. in. 
At centre, theoretical value of deflection = *0328 in. 
„ experimental „ „ = 040 — '008 = '032 in. 
