378 REPORTS ON THE STATE OF SCIENCE, ETC. 
Local concentrations of stress may be deduced also from experiments on elastic 
materials, and one of the authors! helped to measure these stresses in an exact 
representation of the filled rivet-hole of practice. A number of holes were made in 
a slab of rubber (9 in. wide, 3 in. thick) and accurately plugged with the same material. 
Fic. 11 
The results are represented in fig. 11, and show that the maximum longitudinal stress 
at the sides of the holes is nearly double the mean stress. It will be noticed that, owing 
to the hole being filled, this longitudinal stress is accompanied by a transverse 
compressive stress. 
Many other cases, including plates with circular perforations, have been investi- 
gated by Prof. Coker,” using perforated strips of celluloid and polarised light for 
determining the stresses.* 
In cases that can be compared, the results obtained experimentally agree with 
the conclusions drawn from mathematical investigation, and the experiments on 
groups of holes show that when a number are pitched on a transverse section the 
maximum stress concentration is less than the three-times mean value applicable 
to a single hole in a wide plate, and depends on the ratio of the diameter to the pitch. 
1 Institution of Naval Architects, April 1911: experiments by Wilson and Gore 
described in discussion on Prof. Coker’s paper. Also see Hngineering, April 21, 1911. 
» See Edinburgh Report of this Stress Committee; also Cantor Lectures, Royal 
Society of Arts, 1913. 
* That stresses measured in celluloid and other materials truly represent the 
stresses sought within a negligible margin of error has been completely proved by 
Prof. L, N. G. Filon, F.R.S8., Edinburgh Report of this Committee. 
