68 3 
x88o.] On Heat and Light . 
lengths of waves— representing the infinity of intermediate 
— striking the retina in the manner described. If I 
must penetrate the mystery, I confess that it seems easier 
to comprehend the emission than the undulatory theory. I 
know that all things are growing older, and therefore under- 
going an unceasing change, and I cannot understand how 
such change can take place without the emission of something . 
What is that something ? It seems to me that it is the 
cause of all the changes perpetually taking place in Nature. 
It is by this emission (or by this absorption) that I become 
acquainted with the several qualities of things and their 
relationship to my own organism. Something is constantly 
passing between all bodies, by which they aCt and read! 
upon each other ; by which they are at once separated and 
united ; by which all change— mechanical, chemical, and 
physiological — is produced, and which is at the same time 
the origin of life and the cause of decay. This something 
appeals to our senses in many phases has heat or cold, as 
odours, as sounds, as colours differentiated into forms or 
sizes, as tastes, as the various impressions of touch or 
feeling, &c. This something, in its many forms and quali- 
ties, in its attractions and repulsions, and, in short, by the 
infinity of its phenomena, constitutes the reality of which 
gravity is the abstract conception. For, as Newton himself 
suggested, gravity is due not to “ occult qualities supposed 
to result from the specific forms of things, but as general 
laws of Nature by which the things themselves are formed; their 
truth appearing to us by their phenomena , though their causes 
be not discovered.” 
Nor are the impressions of distant objects communicated 
through the senses of no physical account in building up 
the living organism. Such impressions fix themselves more 
or less permanently in the memory, and assist in creating 
the brain tissue by which memory itself is established. The 
brain may, in faCt, be described as a storehouse of such im- 
pressions, in which are gathered not only the experience of 
the living individual, but of all his ancestors to the remotest 
conceivable beginning. And as is the brain, so is the body. 
The inconceivably attenuated matter (or something) which 
strikes upon our senses from surrounding objects may be 
said to have in it “ the promise and potency of every form 
and quality of life.” 
Of all the impressions received from outward objects, 
those of heat and light are the most aCtive in producing 
change. Heat is the moving agent in all manufacturing 
processes having for their object the speedy conversion or 
