10 
MR. E. RUTHERFORD OH A MAGHETIC DETECTOR OF 
The effect on the detector was found to be practically independent of tlie sectional 
area of the receiving wires. A thin wire and a thick rod of the same leno-tb had 
O O 
equal effects ; a plate of metal, G centims. wide, produced the same deflection as a 
thin wire. 
If two wires instead of one were used in parallel the effect was the same as one, 
though the wires were some distance apart. Any number of wires in parallel had 
the same effect as a single wire or plate. 
No difference could be detected whether the first half oscillation in the receiver 
tended to magnetize the needle or the reverse. Since the vibrator used was nearly 
dead-beat, this shows that the damping of the oscillations in the receiver is very 
small. On introducing a short carbon rod in the circuit the deflection was greatly 
reduced. 
It was found impossible to magnetize soft iron or steel when placed in the 
receiving circuit on account of the slow decay of the amplitude of the oscillations. 
The detector needle may be kept in position for a succession of observations, provided 
the current in the receiving circuit is steadily increasing for each experiment, other¬ 
wise the detector should be remagnetized and placed in position again after each 
observation. The deflection was found to be very constant for a series of experi¬ 
ments under the same conditions. 
The connection between the intensity of the electric force at the receiver and the 
deflection of the magnetometer needle can be easily determined by swinging the 
receiving: wires through different angles. 
When the receiver is placed symmetrically with regard to the vibrator, the 
deflection was a maximum when the receiving wires were parallel to the axis of 
the vibrator, and the intensity of the electric force acting along the receiver varies 
as the cosine of the angle from the maximum position. 
With plate vibrators the deflection was found to be nearly independent of the 
degree of brightness of the spark terminals and remained sensibly constant for long 
intervals. In the case of the small cylindrical vibrator used by Hertz with the 
parabolic reflectors, the deflection continually varied with the state of the sparking 
terminals, and such small vibrators cannot be relied on for metrical experiments. 
Some experiments were made to see if the magnetic force in the wave front could 
be directly detected. A collection of thin wires, insulated from each other and 
magnetized to saturation, were used and placed in the direction of the magnetic 
displacement, but the values of the magnetic force were too small to be observed, 
except quite close to the vibrator. 
1 Fores along Wires. 
It was found that the use of a detector, composed of fine insulated wires, was quite 
delicate enough to investigate waves along wires when there was only one turn of 
