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PROCEEDINGS OF THE AMERICAN ACADEMY 



loads. In reading the micrometer, the principle of electrical contact 

 was taken advantage of. 



The greatest errors liable to occur in using the machine are as 

 follows : — 



In measuring the deflections, one ten-thousandth of an inch. In the 

 breaking load, possibly one pound; but in the small loads there could 

 be no appreciable error. In measuring the dimensions of the test 

 pieces, two thousandths of an inch. 



The experiments were conducted with the utmost care, and every 

 possible precaution was taken to prevent errors. 



In arranging for the experiments, and while making them, the 

 writer was greatly assisted by Mr. Holman, of the Institute, to whom 

 he extends his acknowledgments. 



The pieces of wood experimented on were sawn from a spruce 

 plank that had been cut in eastern Maine in the spring of 1880, and 

 the following summer shipped to Boston, where it had lain in the open 

 air until it was cut up in October. The pieces were carefully planed 

 to an approximate size of one and a half inches square and four feet 

 long. 



They were nearly all straight-grained and had but few defects, and 

 in testing the beams they were placed so that the defects should have 

 the least possible effect upon the strength of the beams. The exact 

 dimensions of the test pieces ai'e given in Table I. 



TABLE I. 



In making the experiments, each beam was first subjected to a load 

 of thirty pounds, and the deflection noted. The weight was then h*ft 

 on the beam for a period of time varying from one to four, and in one 

 case forty-four hours, and the deflection again noted. The load was 



