APPARATUS FOP MEASURING STRAIN AND APPLYING STRESS. 



281 



As will be seen from the last column, the values obtained differ very little, in no 

 case varying more than one-half of one per cent. 



The above experiments were carried out for me during the latter part of 1898 and 

 the beginning of 1899 by Mr Colpitts — then a student in the Civil Engineering De- 

 partment of the University. As a test of the accuracy of these results, a third bar was 

 prepared, having a diameter of 0*375 inch; length 8 '00. A new objective was fitted 

 to the measuring instrument, rendering it much more sensitive. The calibration value 

 gave 1 minute of arc = 62 '4 divisions of the scale. This necessitated low torques, in 

 order to prevent the observation wire from passing out of the field of view. A new pulley 

 was used, having a diameter of 20'82 inches, and weighing with hangers, etc., 120 

 pounds. 



A test was first made with no tension load beyond that of the pulley, and imme- 

 diately afterwards a load of 2400 pounds was applied, corresponding to an increased load 

 of 21,700 pounds per square inch. The readings obtained are shown in Table VI. 



Note. — Considerable difficulty was experienced in making accurate readings when the 

 tensional load was applied, as the time of vibration of the heavy weights with respect 

 to the specimen was so large that any accidental motion due to the putting on or taking 

 off the weights was very difficult to damp out. 



A deep four-armed vane was attached to the hanger and dipped into a water-trough 

 on the floor ; this effected a great improvement, but did not wholly counteract the 

 vibration. The readings obtained in Table VI. show a slight diminution when a ten- 

 sional load is applied, but owing to the difficulties of observation mentioned above, the 

 author feels he cannot lay much stress upon them. The observations were repeated 

 with very nearly the same result. As will be seen in the next section, bending affects 

 the angular distortion in the same manner. 



Table VI. 





No Tension except Weight of Pulley. 



Tension, 2400 lbs. - 



t- Weight of Pulley. 



Load in each Pan 

 in lbs. 





















Reading. 



Difference. 



Reading. 



Difference. 



0-4 







196 







194 



0-5 



196 



195 



194 



195 



0-6 



391 



195 



389 



193 



0-7 



586 



197 



582 



195 



0-8 



783 



196 



777 



196 



0-9 



979 



195 



973 



194 



1-0 



1174 





1167 





