355 
1911-12.] The Elastic Strength of Flat Plates. 
was then used. The rigidity modulus thus obtained was 11,210,000 lbs. 
per sq. in. A piece of ^ in. thick plate was then cut out and turned in 
the lathe to a diameter of about ’085 in., and made 6 in. long. The method 
of oscillation was used as above, but, to give variety, the applied moment 
of inertia was not a heavy disc, but a special apparatus used for such 
experiments in the laboratory. By this method, the modulus was 11,280,000 
lbs. per sq. in. The average is thus 11,245,000. Several other experiments 
gave values differing but slightly from the above. Therefore Poisson’s ratio 
and 
2N 
1 
“3-19 
m = 3T9. 
For the fine work accomplished in preparing the specimens for the 
rigidity test, and indeed for the very accurate machine work throughout, 
that alone gives value to these experiments, the author has to thank 
Mr G. H. Long worth, workshop instructor at this Institute. 
Readings for Deflection , Permanent Set , etc. 
These were taken in three ways, as follows : — 
1. The whole apparatus rested on a planed and scraped cast-iron base 
specially constructed for it, and on this base were erected two standards. 
A g-in. turned and polished steel bar, clamped to these standards, could be 
placed in any position and at any desired height over the plate. Readings 
were then taken between the face of the plate and the under surface of 
the bar by means of an inside micrometer gauge ; and it is worthy of 
note in this connection that, by virtue of taking thousands of readings, 
the sense of touch became so fine that this direct method became perhaps 
the most accurate and convenient way of taking deflections. The micro- 
meter used was marked to ^poo i n *> hut readings could be taken with some 
accuracy to 5 0,000 i n - 
2. By means of a dial test indicator used in accurate machine tool 
work on the lathe for measuring eccentricity of the turning piece, and 
manufactured by Messrs Starrets. This was marked to ^oW i n -> hut 
readings to 50,000 i n - cou lh be taken with almost dead accuracy. This 
little tester, no larger than a watch, was clamped to the side of the 
apparatus, and its pointer rested exactly on the centre of the flat plate. 
It was used chiefly on square and rectangular plates to obtain the pressures 
at which set first occurred, because it is a much more difficult matter to 
