17 
minds cannot grasp but which appears to us as infinite in 
time, and working in infinite space, alike unwearied and 
unchanging. Man has found no decisive answer to his questions 
ever since he began to ask them. At onetime man believed the 
moving sun, the moving and changing moon, the moving planets, 
were beings with appetites like his own ; now we know that they 
move by obedience to the law of gravitation, and that some of 
the motions are optical effects only ; but we do not know why 
the law of gravitation exists. We, with our mastery over some 
of the inexplicable forces of nature, yet have just as little 
ultimate absolute knowledge as the men who fancy themselves 
kin to beasts, or who venerate an erratic block. 
At the conclusion of Mr. Davey’s Paper, Mr. D. HE. Caush gave 
a demonstration on ‘‘ Mounting Microscopical Objects.” 
WEDNESDAY, DECEMBER, 9th, 1891. 
A PIANO OF COLOURS, 
BY 
MR. L. LEULIETTE. 
The analogy between light and sound has for long been a 
subject of interest to musicians as well as to physicists. They 
are both the result of wave motion. The waves of air which 
produce in our brain the sensation of music are indeed slow 
compared with that continuous ripple which on our retina gives 
us the sensation of colour. Nevertheless NumBER is at the base 
of both phenomena. It is to the difference in the number of 
air-vibrations that variety of tones are due, and it is to a 
_ difference in the number of ether-vibrations that variations of 
colour are due. Moreover, there is a gamut of colours as there is 
an octave of sounds, or at any rate there is the natural scale, if 
it may so be termed, running from red through orange, yellow, 
green, blue, and indigo into violet. Now, music which gives 
pleasure to the ear results from certain combinations of notes. 
