361 
1911-12.] The Elastic Strength of Flat Plates. 
experimental values for deflection are exceedingly close to the calculated 
ones. It is well known that such close results are obtained in ordinary 
experiments on the bending of beams, and are considered sufficient proof of 
the accuracy of the laws of bending. And there is no reason that with a 
sufficiently delicate apparatus the values for plates should be less accurate 
than those for simple beams. 
As a final result for deflection, the following experiment is given. The 
plate was circular and 4 in. diameter. Its thickness was ‘055 in., and 
certainly did not vary more than *0002 in. on either side of this. The 
values on part of the straight line are as follows : — 
Plate G. 
Pressure in ibs. 
per sq. in. 
Micrometer readings, 
in inches. 
Difference in 
deflection, in inches. 
65 
•0655 
0 
70 
•0635 
•002 
75 
•0605 
•003 
80 
•057 
•0035 
80 (new zero for 
•055 
oil adjustment). 
85 
•053 
•002 
90 
•050 
•003 
95 
•047 
•003 
100 
•045 
•002 
105 
•042 
•003 
110 
•040 
•002 
115 
•037 
•003 
120 
•034 
•003 
125 
•031 
•003 
130 
•028 
•002 
The sum of the differences gives ’0345 in. for a range of pressure of 
65 lbs. This is equivalent to a deflection of -01061 in. for a pressure of 
20 lbs. per sq. in. The theoretical value is ‘01101 in. 
The 4 in. diameter circle was the most unfavourable for taking measure- 
ments, for, owing to its small size and the large amount of fixing area, the 
zero error was apt to be more troublesome than with the larger sizes. 
Bearing in mind this fact, the experimental and theoretical results are 
remarkably alike. And in general the author concludes that such a 
number of experimental results so closely focusing upon theoretical values 
could not have been obtained unless the theory was correct within half per 
cent, or less. 
Since the deflection formula contains p, r 4 , E, t s , and constants, it might 
be sufficient to consider the matter proved. But it was determined to place 
