395 
Natural Philosophy. — Electricity . 
order ; the intensity gradually increased as it had before dimi- 
nished, and when the two parts were nearly parallel, it became 
as powerful as in the rectilineal transmission. By multiplying 
the right angles in a rod, the transmission of the vibration may 
be completely stopped.” 
In these experiments, the axis of the oscillations of the tuning 
fork should be perpendicular to the plane of the moveable an- 
gles ; for if they are parallel, they will still be transmitted. Mr 
Wheatstone gives the following explanation to prove this. u I 
placed a tuning fork perpendicularly on the side of a rectilineal 
rod. The vibrations were therefore communicated at right an- 
gles ; when the axis of the oscillations of the fork coincided with 
the rod, the intensity of the transmitted vibrations was at its 
maximum. In proportion as the axis deviated from parallelism, 
the intensity diminished, and when it became perpendicular, the 
intensity was a minimum.” The phenomena of polarisation may 
be observed in many chorded instruments. The chords of the 
harp are attached to a conductor which has the same direction 
as the sounding-board ; if any chord be altered from its quiescent 
position, so that its axis of oscillation shall be parallel with the 
bridge or conductor, its tone will be full ; but if the oscillations 
be excited, so that their axes shall be at right angles with the 
conductor, the tone will be feeble. ^ 
12. On the Oscillations of Sonorous Chords — The following 
theorem on this subject is very important in acoustics, and re- 
moves all obscurity from the subject of harmonic sounds. 
“If any two sonorous chords A and B be so placed, that the 
oscillations of one shall cause the air to act upon the other, as in 
all stringed musical instruments ; and if A oscillates m times, 
while B oscillates n times, m and n being any whole numbers 
prime to each other ; then if either of the chords, as A, is put in 
motion, the action of the air will divide B into m equal parts, 
which will oscillate n times, while A oscillates only once.”— 
Quarterly Journal , No. xxx. p. 374. 
ELECTRICITY. 
13. Improvement on the Electrical Machine. — Having re- 
marked the great efficiency of electrical machines, when a hot 
cloth was held under the cylinder, and observed, that this addi- 
tional power lasted only while it continued warm, Mr Ronalds 
