16 



Mr. J. Morrow. On the Distribution of [Oct. 27, 



Method of Making the Experiments. 



For the first series of experiments, a long cast-iron bar, 2-833 cm. 

 broad and 6 -452 cm. deep, was placed in the " Wicksteed " testing 

 machine, in the Engineering Laboratory at University College, 

 Bristol. It was supported on knife edges at each end of a span 

 of 91 '44 cm. (36 inches), and was loaded in the centre in the ordinary 

 way. 



At a distance of from about 7 '5 to 9*0 cm. from the centre of 

 the span lines were carefully scribed on the sides of the beam, 

 marking the places where the set-screws of the strain-measuring 

 instrument were to rest. One of these lines was at the middle of the 

 depth, and the others at distances of 0-635, 1-905, and 3*175 cm., both 

 above and below the mid-point. 



The instrument was attached just clear of the ends of these lines, 

 and 36*80 cm. from one of the planes of supports. Thus the section 

 examined was at a distance from the point of application of the load 

 exceeding the depth of the beam, and it was hoped that this would be 

 sufficient to secure immunity from the effects of local strains due to 

 surface loading. Under these circumstances, each ton applied at the 

 centre would produce a bending couple of 18,694 kilogram-centimetres 

 at the section under observation. 



The effective distance between the needle points of the tilting 

 mirror, as given by a reading microscope, was - 6160 cm., and the 

 normal distance of the scale from the mirrors 202*7 cm. 



The total magnification was, therefore, 2632 for the first experi- 

 ments, but it was, of course, re-determined whenever the position of 

 the scale was altered. 



The scale was divided to ^th of an inch, and, with the telescope 

 used, yoth of these divisions could be readily estimated. The observed 

 numbers are, therefore, given to the nearest TT T3 iro °^ a centimetre. 



When taking a series of readings for a certain change of load, the 

 instrument was first applied with the points AA at the lowest mark, 

 and a number of readings taken each time the load was applied or 

 removed. The set-screws were then moved up to the next mark, and 

 the readings continued. When the centre was reached, the instrument 

 was taken off and re-applied above the specimen, with the screws BB 

 at the top marks, and observations were continued down to the centre 

 again. 



The log sheet was kept as follows : — 



