382 Proceedings of the Royal Society of Edinburgh. [Sess. 
From the above table it will be seen that in nearly every case the 
experimental value is greater than that given by Grashof, and the author 
believes engineers would be on the safe side if, when calculating stress 
values for square and rectangular plates, they multiplied Grashof ’s equations 
by 1*25. 
The Position of the Ribs in Square and Rectangular Plates. 
The analysis for curvature of these plates shows beyond doubt that the 
maximum stress is at the ends of the diameters. The natural position for 
ribbing would therefore be parallel to the sides, the primary ribs being at 
right angles across the centre, and not along the diagonals. Furthermore, 
the ribbing, if it altered at all, should be thickest at the edges and not at 
the centre. The function of ribbing, of course, is understood to prevent any 
portion of the plate from passing the elastic limit, and thus bringing the 
strength of flat plates into line with that of other engineering pressure 
members. 
Some Effects observed during the Progress of the 
Investigation. 
Reversing the Plate. — A circular plate 6 in. diameter and TOO in. thick 
was tested for central deflection in the ordinary way, the maximum 
pressure used being insufficient to cause it to pass beyond the elastic range. 
The plate was then reversed and again tested, but no practical difference 
was noted in the magnitude of the deflections, except those produced by 
the low initial pressure. 
Initial Slight Permanent Set. — A circular plate 6 in. diameter and *066 
in. thick was subjected to a pressure of 45 lbs. per sq. in., which produced 
a slight set. The pressure was then entirely removed and gradually 
reapplied. No practical difference was noted in the second series of 
deflection readings. 
Slight Loosening of the Clamped Edges. — Several tests in which the 
fixing bars were not clamped hard down gave consistent results. In no 
case could a perfectly straight elastic line be obtained. The curve of 
pressure and central deflection bent slightly but persistently upwards. 
Initial Heavy Permanent Set. — A plate 6 in. by 6 in. square and 
"0653 in. thick was subjected to heavy set. The plate was then tested for 
deflection in the ordinary way. The result is given in Diagram 11. The 
general effect was to considerably lessen the deflections and make them 
below true values. 
