OF IHOIf BEAMS. 449 



the future experiments on small beams, since 

 the results would be more useful in that form. 



37. The form we first adopted was one in 

 which the arc AEB (figure to Art. 29) was a 

 semielHpse, and the bottom rib a straight line; 

 but the sizes of the ribs at top and bottom were 

 in various proportions ; the ribs in the model were 

 first made equal, and when a casting had been 

 taken from it, a small portion was taken from 

 the top rib and attached to the edge of the 

 bottom one, so as to make the ribs as 1 to 2 ; 

 and when another casting had been obtained, 

 a portion more was taken from the top, and 

 attached to the bottom as before, and a casting 

 got from it, the ribs being then as 1 to 4. 



In these alterations the only change was in 

 the ratio of the ribs, the depth and every other 

 dimension in the model remaining the same. 



38. In most of the experiments the beams 

 were intended to be broke by a weight at their 

 middle, and therefore, the form of the arc 

 AEB was of less importance ; in making them 

 elliptical they were too strong near the ends 

 for a load uniformly laid over them ; the proper 

 form is something between the ellipse and 

 parabola. It is shewn, by most of the writers 



3 L 



