59§ 
Sunlight. 
"October, 
VIII. SUNLIGHT. 
HEN we consider the countless ages that the sun 
V^y has given out his daily light and heat, without our 
most delicate instruments being able to deteCt any 
loss in substance or energy, we are apt to conclude that 
there is something wanting in our theories to explain how 
such constancy is brought about. 
The law of gravitation gave the key to what had been 
previously inexplicable in planetary motion. It showed us 
how mass was attracted by mass, and how world was influ- 
enced by world ; but we seem to have altogether overlooked 
the force which must result from this universal attraction 
and this never-ending motion. Is it here that we are to 
seek for the force that builds up a sunbeam ? 
If we rub a glass rod with a piece of silk it becomes warm 
through friction, but independently of this its attractive 
properties are greatly increased, and it is found to emit light 
and heat when brought into contact with the earth. What 
has brought about this change ? The answer is Motion. 
But motion alone would never have had these after effects 
unless there had been a prior mutual attraction between the 
two bodies. This imperceptible attraction was overcome by 
the motion, and the result was that the attraction was not 
only increased, but the surplus force appeared, in a spark, as 
light and heat. 
If under peculiar circumstances one magnet is revolved in 
front of another, the same effects are observed, although in 
this case there is no contact between the two bodies. If we 
disturb the attraction which holds together the atoms of a 
chemical compound, whether it be in the solid, the liquid, or 
the gaseous state, we have this same emanation of light and 
heat. If, then, these great effects can be produced in our 
laboratories, what must result in our Solar System from 
the continual struggle between attraction and centrifugal 
force ? 
In our own system we find our glass rod replaced by a 
rolling world 882,000 miles in diameter, round which is con- 
tinually circling a host of other worlds. Here there is no 
contact, therefore no friction to retard and disarrange the 
whole, but there is a mystic tie that binds them all together 
— there is, in faCt, attraction. When this attraction is 
disturbed by motion the result must be as in our former 
