[REILLEY-HENRY] CONTACT RESISTANCE IN OIL 147 
PRESENT EXPERIMENTS. 
The series of experiments described herein were undertaken for 
the purpose of determining accurately the minimum pressure required 
to produce good contact between metal wires. In order to obtain this, 
careful observations were made of the change in contact resistance 
_ between what we may term open circuit, or infinite resistance, to 
that of good contact. It was necessary, therefore, to arrange the 
apparatus so that the contact resistance could be observed 
simultaneously with the applied pressure. In this way a great 
many observations were taken showing how the contact resistance 
decreased with increasing pressure for metal wires both in air and in 
various oils. It was hoped that some light might be thrown on the 
nature of contact resistance and also to show the advantage of using 
oil for increasing the efficiency of electrical contact. 
These experiments are a continuation of the work done by Mr. 
Reilley. The same apparatus was used and the same means of chang- 
ing the pressure. See Figure I. 
Te a 
To Exnaust Pump |. 

Figure 1. 
B, is a glass beaker partly filled with water. 
Ti is a tap. 
T. is a three way tap. 
C, is a tube containing 1 c.c. By changing the level of water 
in C, the weight of water taken out or put into B is known. 
L, lead weight used to balance pan. 
W,, wire soldered to movable jaw, J. 
Wo, wire firmly clamped. 
By moving J up, Wi is brought into contact with W2. This is 
done by changing the weight on left hand balance pan. Y, is a clamp 
to support C. 
