452 Proceedings of Royal Society of Edinburgh. [sess. 
A Laboratory Apparatus for Measuring the Lateral 
Strains in Tension and Compression Members, with 
some Applications to the Measurement of the 
Elastic Constants of Metals. By E. G. Coker, M.A. 
(Cantab.), D.Sc. (Edin.), F.R.S.E., Professor of Mechanical 
Engineering and Applied Mathematics, City and Guilds 
Technical College, Finsbury, London. (With a Plate.) 
(MS. received October 26, 1904. Read November 21, 1904.) 
The recognition of the importance of lateral strain in the theory 
of elasticity, as now taught in most engineering colleges, makes 
it very desirable that students should make experiments upon the 
lateral contraction of tension specimens and the lateral extension 
of compression pieces with the same facility that they now deter- 
mine the values of Young’s modulus and the modulus of shear. 
With this purpose in view, the author designed an instrument 
which has been very thoroughly tested by student-use for the 
past two years in the testing laboratory of M‘Gill University. 
For the object in view it was necessary to make an apparatus 
of simple construction, easily operated and understood, and 
capable of standing a considerable amount of wear and tear without 
injury, while at the same time it must be capable of measuring 
with accuracy linear strains of the order of o-q.^oo an inch. 
After some minor alterations, an apparatus was constructed 
which fulfilled these requirements. 
The instrument is shown in sectional elevation by fig. 1, and 
in part sectional plan by fig. 2, and it consists essentially of 
a pair of tubular arms A, connected by a 'flexible steel plate B, 
which forms the fulcrum. This plate is very thin, in order to 
allow the arms to turn in the plane passing through their axes, 
and is very deep, to give the necessary rigidity perpendicular to the 
plane of motion, and thereby ensure that the arms have no other 
motion. The plate is gripped by a pair of collars C, mounted on the 
arms A, and provided with grooved ends and tightening screws. 
The instrument is attached to the specimen by a pair of screws 
D, threaded through nuts formed on the arms and provided 
