68i 
1880.] 
On Heat and Light . 
moment exadtly what he was the moment which immediately 
P Now what is change but motion? And yet it is more 
than motion : however imperceptible it may be, it is part 01 
the process of transformation by which the wine is improved, 
and by which the child becomes a man. The effect is not a 
mere mechanical rearrangement of parts,— not only a 
“vibration ” or “ clashing of atoms,” but a constitutional 
or radical difference, however small, between tne original 
and present states. Either “ something” has been taken 
or something has-been added ; and is it not probable that 
something has been both taken and added, by which the 
change has been produced ? We may call that something 
“ matter,” or we may call it “ an accident or condition ot 
matter the change could not have taken place without 
motion* but neither could it have been produced by motion 
a lone 
In the volume to which I have referred I have, shown 
that on the assumption that all things exist by virtue of 
their circumstances, it follows that “ a change in the cir- 
cumstances of things necessarily involves a corresponding 
change in the things themselves.” . This I have described 
as “the Law of Motion.” Hence it is that as Nature is 
never at rest, as worlds and systems of worlds are always 
moving, and as all the other bodies of space, small or great, 
are perpetually taking up new positions in relation to each 
other— every bit of matter in the universe, every atom or 
molecule, is perpetually undergoing a process of change. 
Mav we not assume that heat is one of the forms of this 
change ? It is undoubtedly true that, according to the 
extent or degree of this change, we must have motion ; and 
according as this motion in extent or degree appeals to our 
sense of feeling, by adding to or subtracting from the na- 
tural warmth of our bodies, we employ the terms heat or 
cold to express our estimate of the character of the pheno- 
m The truth is that all things in Nature are united together 
by a constitutional relationship, of which the action of heat 
upon our organism is one of the manifestations. W e be- 
come mentally acquainted with this relationship by means 
of the senses of seeing, feeling, hearing, tasting, &c. When 
I look round the room in which I am sitting, I see articles 
of various forms, sizes, and colours, — e.g., chairs, tables, 
piftures, &c. Why do I see them ? I may be told that it 
is because rays of light are reflected from the objects to my 
organs of vision ; and it is true that without light I could 
