AND STRAIN ON THE ACTION OP PHYSICAL FORCES. 
31 
in the one the wire was lengthened by successive loads put on for three minutes each 
and then removed; in the other the wire was stretched by the hand or by the aid of 
a lever by equal amounts each time until breaking ensued. The balance used in 
determining the density was an exceedingly good instrument made for me by 
Oertltng for the purpose of measuring the coefficients of thermal expansion of the 
metals by weighing them in water at different temperatures. It will suffice here to 
state that it was possible with this instrument to weigh an object in water to -j^th of 
a milligramme. The air bubbles clinging to the sides of the metals were carefully 
brushed off, as it was not possible to boil them off, for fear of partially annealing the 
wires, and the proper corrections were made for temperature and air displaced. The 
following experiments serve to illustrate the general nature of the results obtained by 
the two methods :— 
Experiment XX I. 
Silver (1). 
Load in kilogs. used 
in producing 
extension. 
Specific gravity water 
at 4° C. = 1. 
Total percentage of 
increase of length 
=dl. 
Total percentage of 
decrease of specific 
gravity = dA. 
dA 
dl' 
1 
10-47691 
6 
10-47561 
1-15 
•0124 
•0108 
7 
10-47207 
3-64 
•0461 
•0127 
775 
10-46754 
7-28 
•0892 
•0123 
8-25* 
10-46153 
9-38 
T465 
•0156 
Experiment XXII. 
Copper (1). 
Load in measures of 
water, each measure 
= 2‘5 kilogs. 
Specific gravity water 
at 4° C. =1. 
Total percentage of 
increase of length 
= dl. 
Total percentage of 
decrease of specific 
gravity = dA. 
dA 
~dT 
5 
8-8252 
9 
8-8251 
2-58 
•00113 
•00044 
10 
8-8247 
4-21 
•00566 
•00134 
11 
8-8102 
6-94 
•1699 
*02448 
12 
8'8076 
10-74 
•1993 
‘01856 
13 
8-7968 
16-27 
•3216 
•01977 
* Wire broken. 
