367 
1911-12.] The Elastic Strength of Flat Plates. 
The following are the results obtained : — 
Square plate. 
Thickness, 
Reference 
number. 
Deflection corrected 
for zero error, for 
pressure 20 lbs 
per sq. in. 
Theoretical 
deflection. 
6x6 
•065 
1 
•050 
•04997 
6x6 
•069 
2 
•042 
•04178 
6x6 
■067 
3 
•043 
•04561 
5^x 5^ 
•064 
4 
•031 
•03695 
5x5 
065 
5 
031 
•02409 
5x5 
•055 
6 
039 
•039 
5x5 
TOO 
7 
•008 
•006616 
5x5 
•064 
8 
•026 
•02523 
5x5 
•0635 
9 
•027 
•02595 
4^ x 4\ 
•061 
10 
•017 
•01912 
4jx4i 
•070 
11 
•016 
•01265 
4x4* 
•066 
12 
*017 
•01510 
4£x4£ 
•065 
13 
•0165 
•01581 
4x4 
•060 
14 
•015 
•01254 
4x4 
•0635 
15 
•013 
•01058 
The results for the five plates may be stated concisely as follows : — 
Square plate. 
Average 
experimental 
deflection. 
Average 
theoretical 
deflection. 
6x6 
•045 
•04578 
5-| x 5^ 
•031 
•03695 
5x5 
•0262 
•02417 
4^x41 
•0166 
•01567 
4x4“ 
•014 
•01156 
Grand average 
•0265 
•0268 
The average theoretical and experimental values are so close that there 
can be little doubt that the deflection formula for the square plate as given 
by Grashof is correct enough. 
An attempt was made, however, to obtain the pressure at which set 
commenced for these plates. The maximum stress (or, what is equivalent 
to the maximum stress, the maximum strain by Young’s modulus) is 
given by : 
- 1 ptf 
J 4 
It is to be noticed that, with the square plate, one fibre of the plate 
passes outside the elastic range first, and that there then follows a gradual 
elastic breakdown of the other fibres. In the circular plate, on the other 
