490 THE STRENGTH 



of the deflections, inaccuracies could scarcely 

 be avoided; they were not in these taken in 

 the middle of the beam, but three inches from 

 it, as it was more convenient to take them there 

 than in the middle. 



51. If we examine the deflections in experi- 

 ments 18, 20, and 21, we shall find that in 

 the first and third about t, and in the second 

 upwards of i the breaking weight was laid on 

 without the elasticity being in appearance at all 

 injured. Now this is contrary to former expe- 

 rience, it having been generally found that the 

 elastic force was sensibly injured with about 

 one third of the breaking weight (Tredgold's 

 Essay, Page 79). And as experiments have 

 mostly been made upon rectangular pieces, the 

 above fact, if properly ascertained, will render 

 it probable that change of form may have an 

 influence upon this ratio ; and may in some 

 forms remove the point of incipient derange- 

 ment from J to i or even | of the breaking 

 weight. 



52. In the preceding experiments the beams 

 being short, and the deflections small, there 

 was considerable difficulty in ascertaining the 

 precise point, where the above defect took place ; 



