20 
^^[R. E. RUTHERFORD OH A MAGNETIC DETECTOR OF 
(8.) A thin soft iron cylinder, 1‘9 centims. in diameter. Increase of resistance, 
3‘9 ohms. 
(4.) Solid iron rod. Increase of resistance, 3'3 ohms. 
(5.) A copper cylinder, a test-tube filled with a copper sulphate solution, and a 
platinum cylinder showed no appreciable absorption of energy. 
(6.) A carbon rod absorbed a large ammunt of energy. Increase of resistance, 
3’3 ohms. 
Table of Absorption of Energy of various Conductors; Absorption of Energy 
expressed in Terms of the Increased Resistance of the Discharge Circuit. 
Substance. 
Increase of resistance. 
Laminated soft iron wires . 
Solid soft iron cylinder .... 
Hollow iron cylinder. 
Carbon cylinder. 
Copper, platinum, zinc cylinders . 
Steel tilings. 
I0'25 obins 
3'5 ,, 
3-9 „ 
3'3 ,, 
not appreciable 
9 ohms 
The frequency of the oscillations in the above experiment was two million per 
second. 
If the experimental value obtained for the increase of resistance due to the solid 
iron cylinder be compared with the theoretical value (‘ Recent Researches,’ p. 323), the 
value of the permeability will be found to be 172, which accounts for the much greater 
absorption by an iron cjdinder than a copper one. 
From the peculiar deadened sound of the spark, it could always be told when much 
energy was being absorbed in the discharge circuit. With copper wires for the 
discharge circuit, the spark was sharp and bright ; when iron wires were substituted, 
the spark was weak ; when an iron cylinder was put in the place of a copper one, the 
spark was neither so bright, nor so sharp in sound. 
Determination of the Period of a Discharge Circnit. 
It is often a difficult matter to obtain even an approximation of the period of 
oscillation of a discharge circuit when the capacity of the condenser and the self¬ 
inductance of the circuit cannot be directly calculated. 
The following simple method was found to work very accurately in practice, and 
could be used for a fairly wide range of frequencies. 
Let ACB, ADR (fig. 5) be two branches of a discharge circuit in parallel, R and L 
the resistance and inductance of the branch ACB, S and N the resistance and 
inductance of branch ADB. 
