1905.] The Effects of Momentary Stresses in Metals. 503 



Micrometer set at 110-5 (76 divisions extension). No contact when 

 weight let fall. 



Repeat the blow. No contact. Repeat. No contact. 



Micrometer with steady load of 50 Ibs. now reads 34-5. 



Micrometer set at 109-5 (75 divisions extension). No contact. 



Altered to 108 -5. Contact occurred; the galvanometer spot went 

 half across the scale. 



Repeat. Contact again. 



Steady micrometer reading after this 36*0. 



Micrometer set at 111 (75 divisions extension). No contact. 



Repeat. No contact. Repeat. No contact. 



Steady reading now 36*0. 



Micrometer set at 110 (74 divisions extension). No contact. 



Repeat. Contact occurred. 



Steady reading now 37 '0. 



Hence, the instantaneous extension in this case is 74 micrometer 

 divisions, and the permanent extension produced by 11 blows is about 

 2-5 divisions. 



Then followed a set of 4 blows with a 10-foot fall, and with 20 Ibs. 

 tension. They resulted as follows : 



Steady reading 7*0. Set at 110 (103 divisions). Contact. 

 Steady reading 20'0. Set at 125 (105 divisions). No contact. 

 Steady reading 29'5. Set at 132 (102J divisions). Contact. 

 Steady reading 42'0. Set at 148 (106 divisions). No contact. 

 Steady reading 52 '5. 



Hence, the extension produced by the blow is probably between 

 103 and 105 divisions, and almost certainly between 102 and 106. 

 Permanent extension produced by 4 blows = 45 '5 divisions, or just 

 over l/1000th part. 



Now static tests on this wire showed that a load of 390 Ibs. extends 

 it by I/ 1000th part. Also //. its mass per foot is 0'0435 Ib. Hence 



The mass of the stop was 0'04 Ib. Hence V, the velocity just after 

 impact, is, with a 5-foot height of fall, 17 -2 f.s. Also since x = 1-66 feet ; 

 fix' 1-66x0-0435 n n7 

 "M = ~T" 



Further, T = 50 Ibs. = 1600 poundals, and it will be found that 



iT./?^\ 2 is about . 4 thousandth of an inch, or 0-8 micrometer 

 2 M\ a ] 



division. Substituting these figures in the expression (2) above, the 

 extension on the 20 inches, as calculated, is 37'2 thousandths of an 

 inch, or, say, 74 \ micrometer divisions. The observed extension is 

 74 divisions, which is close agreement. This, coupled with the fact 



