68o 
On Heat and Light. 
[November, 
II. ON HEAT AND LIGHT. 
By Robert Ward. 
CCORDING to the modern scientific idea Heat is a 
“ mode of motion.” Prof. Tyndall, who has done 
so much towards popularising this view of heat, 
describes it as “ an accident or condition of matter ; namely, 
a motion of its ultimate particles” He discards the material 
theory which supposes heat to be “ a kind of matter — a 
subtile fluid stored up in the inter-atomic spaces of bodies.” 
Yet for a long time the latter had the greater number of 
supporters eminent in Science. 
It is not my intention to suggest that either the one or 
the other theory is devoid of truth. I have elsewhere shown 
that all things exist by virtue of their circumstances, and 
that, as the circumstances of all things are continually 
changing, all things must be continually changing {see 
“ Constitution of the Earth,” p. 4). That such change is 
always going on is rendered obvious by the amazing fadt 
that everything grows older. Even wine, however preserved 
from contact with surrounding objects by being hermetically 
sealed in a glass bottle, undergoes a change well known to 
the toper, though undiscoverable by the analytical processes 
of the chemist. That this change is a never-ceasing one is 
as evident as that a body falling from an elevated position 
must pass through all the intermediate points of space 
before it reaches the ground. There may be no evidence of 
any substantive addition to, or withdrawal from, the contents 
of the bottle ; nevertheless the wine has grown older , as disco- 
verable by the sense of taste, and by such change, up to a 
certain point, it is humanly speaking “improved.” It cannot 
be doubted that, from the time a human being comes into the 
world till he passes out of it, the entire phenomena of life 
consists of an unceasing change. Infancy, youth, manhood, 
and old age are only terms by which we recognise the more 
prominent phases of a never-ending, still-beginning evolution. 
To indicate their appreciation of such change, chemists 
formerly told us that in seven years every molecule of the 
original substance of the human body had been removed 
and substituted by other molecules. The more modern idea 
is that this takes place at much shorter intervals ; but is it 
not obvious that a human being is never for a single 
