160 Wisconsin Academy of Sciences^ Arts, and Letters. 



I would add a word with regard to obtaining coefficients 

 and formulae for conaputing the strength of materials. As a 

 general thing, experiments are continued until fracture takes 

 place, and a fractional part of the breaking weight is taken as 

 the coefficient of safety. The specimens must also be of lim- 

 ited size in order that they may be broken by ordinary means. 

 Hence the results would be doubtful in two respects: 1st. 

 There would be a flexure not admissible in practice with even 

 a fraction of the breaking weight. And, 2d. The specimens 

 must necessarily be selected, and would differ from material 

 used in practice. (These remarks are in reference to wooden 

 beams.) Mr. Wm. Hearding in making experiments on the 

 retaining power of large bolts in wood, found that the resist- 

 ance to a transverse strain in very strong beams was materially 

 different from accepted data. I would hence suggest, that in 

 experiments the strain producing the extreme flexure admissi- 

 ble in practice be taken as the safe strain ; it would then be 

 possible to use specimens of large dimensions, even those 

 used in practice, and also for comparison to subject some to a 

 breaking strain. Parallel with the strength of materials is an 

 accurate knowledge of the weight of all materials used in 

 construction and especially in their applied form. Consider- 

 ing the subject in question one of great importance, I have 

 determined to make the same a specialty and will convey the 

 result of my investigations to the Academy as occasion may 

 permit 



