351 
1911-12.] The Elastic Strength of Flat Plates. 
obtain the distributed pressure. With low pressures, such as a few pounds, 
this instrument is likely to introduce a considerable error. To avoid this, 
the author used a standard pressure-gauge tester with first glycerine and 
afterwards oil as the working fluid. 
Preliminary Investigation. 
A series of preliminary experiments on circular plates, conducted with 
comparatively simple apparatus, yielded results which were near enough to 
the theoretical values to warrant the undertaking of a more elaborate 
investigation. 
The Rigorous Investigation. 
The Dimensions, Form, and Type of Plates. 
On account of the thinness of the plates (because of the formulae only 
holding good for plates thin in comparison with their other dimensions, and 
owing to experimental reasons) it was found a difficult matter to turn 
them perfectly flat, even by experienced turners, and it became necessary to 
look around for a material that would obviate this difficulty. The material 
must satisfy the following conditions : — 
1. It must be as nearly flat as possible in its natural state, and no part 
of it must be buckled or past its elastic limit. 
2. Its thickness must be of great uniformity. 
3. It must not be too expensive, because of the large number of plates 
required. 
After much consideration it was determined to employ planished steel 
as fulfilling most of the above. This substance can be obtained in various 
thicknesses, ranging from *050 in. to TOO in. It receives such severe 
treatment in the process of rolling that it is perhaps more free from internal 
blemishes than ordinary mild steel sheet. It is very pure, an analysis 
showing over 99*5 per cent. iron. It is consequently very soft, the file 
tearing it with ease. It appears very homogeneous in structure, is supplied 
in flat sheets, and is of great uniformity of thickness. It is very ductile, 
has fairly well-defined elastic limit and yield points, and low breaking 
stress. It is used in practice for cylinder casings and the like. 
The plates employed were of various gauges, and those were selected 
that showed almost perfect uniformity of thickness. The plates were 
mostly first drilled round with a series of small holes, cut out somewhat 
larger than required, and carefully filed down to size. 
As it was necessary to experiment with plates of various forms and 
sizes, it became necessary to devise an apparatus that would do for all or 
