682 
On Heat and Light. 
[November, 
not see them. But neither could I see them without eyes; 
and yet it is evident that, whether I see them or not, — 
whether my eyes are open or shut, — the relationship between 
the objects and my organism, so fay as it is mechanical , must 
always be the same as long as they and I remain unmoved. 
The objedts, in fadt, exist independent of either the light or 
my eyes, but the adtual perception of them is due to certain 
qualities which are impressed upon my organism when the 
necessary relationship is established. Thus there are three 
fadtors necessary to sight — eyes, objedts, and light. The 
qualities by which objedts are revealed to us are colour, 
form, and size. Really, however, so far as the visual per- 
ception of things is concerned, colour is the basis or founda- 
tion of sight, form and size being due to a perception of 
differences in colour, and to the limitation or extension of 
such differences. Thus I can only see the chairs, tables, 
pidtures, &c., by virtue of the light which strikes upon their 
surfaces and reveals to me various colours, .or shades of 
colour, the perception of which (by contrast) is the founda- 
tion of my knowledge. 
As in the case of heat, Light was believed by Newton to 
be due to the emission of a subtile fluid, but modern Science 
repudiates the teaching of the great philosopher as to both 
light and heat, and they are now severally described as 
simple “ modes of motion.” Heat, we are told, is a clashing 
together of the ultimate particles of matter ; whilst Light 
is due to the vibrations of a luminous ether wholly unknown 
to the senses, but which fills all space and penetrates be- 
tween the molecules of all bodies. White light, as it reaches 
us from the sun, is a compound or mixture of many colours. 
The different colours of bodies are said to be due to the 
way they refledt the different kinds of light, by creating in 
the imaginary ether waves of different lengths. These 
waves, though as infinitely numerous as the shades of colour, 
are supposed to move simultaneously and perfectly distindt, 
so that each will produce its own separate and charadteristic 
effedt upon the organs of vision. 
Such is the modern scientific theory as to the creation of 
colours. I must confess that my understanding is not so 
much enlightened by it as by the emission theory of Newton. 
The solar spedtrum exhibits seven principal colours, but 
these imperceptibly merge into each other through an infi- 
nity of intermediate tints. I find it hard to imagine seven 
waves of different lengths, all moving with equal speed and 
striking the retina of the eye at the same moment ; but I 
am totally unable to realise the idea of an infinity of different 
