ON SECULAR EXPERIMENTS UPON THE ELASTICITY OF WIRES. 



35 



the rate of one pound per day, some with three quarters of a pound per 

 day, and some with half a pound per day. One experiment was com- 

 menced in which it was intended to break the wire at a very much slower 

 rate than any of these. It was carried on for some months, but the wire 

 unfortunately rusted, and broke at a place which was seen to be very 

 much eaten away by rust, and with a very low breaking weight. A fresh 

 wire has been suspended, and is now being tested. It has been painted 

 with oil, and has now been under experiment for several months. 



The following tables will show the general results of these experi- 

 ments. It will be seen, in the first place, that the prolonged application 

 of stress has a very remarkable effect in increasing the strength of soft 

 iron wire. Comparing the breaking weights for the wire quickly broken 

 with those for the same wire slowly broken, it will be seen that in the 

 latter case the strength of the wire is from two to ten per cent, higher 

 than in the former, and is on the average about five or six per cent, 

 higher. The result as to elongation is even more remarkable, and was 

 certainly more unexpected. It will seen from the tables that, in the 

 case of the wire quickly drawn out, the elongation is on the average more 

 than three times as great as in the case of the wire drawn out slowly. 

 There are two wires for which the breaking weights and elongations are 

 given in the tables, both of them ' bright ' wires, which showed this 

 difference very remarkably. They broke without showing any special 

 peculiarity as to breaking weight, and without known difference as to 

 treatment, except in the time during which the application of the break- 

 ing weight was made. One of them broke with 44£ lbs., the experiment 

 lasting one hour and a-half; the other with 47 lbs., the time occupied 

 in applying the weight being thirty-nine days. The former was drawn 

 out by 28 - 5 per cent, on its original length, the latter by only 479 per 

 cent. 



Tables showing the Breaking of Soft Iron Wires 1 at Different Speeds. 

 I.— Wire Quickly Broken. 



Rate of Adding Weight 



-J lb. per minute . 



1 lb. „ 5 minutes 



»» 5 ,, 



>» 4 >> 



» •* » 



>> •-* » 



ni 5 », 



1 lb. per 5 minutes 

 >> >> 5 » 



Breaking 



Weight in 



Pounds 



*Dakk Wire. 



*Bright Wiee. 



45 

 451 



44| 

 45| 

 44J 



Per cent, of 



Elongation 



on Original 



Length 



25-4 

 25-9 

 24-9 



24-58 

 24-88 

 29-58 

 27-78 



1 The wire used was all of the same quality and gauge, but the ' dark ' and ' bright ' wire 

 had gone through slightly different processes for the purpose of annealing. 



d2 



