heat and cold, or taste, or
smell are any thing but sensations.

The same philosophers who have called our attention to these remarks,
have proceeded to shew that the causes of our sensations of sound and
colour have no precise correspondence, do not tally with the sensations
we receive. Sound is the result of a percussion of the air. Colour
is produced by the reflection of the rays of light; so that the same
object, placed in a position, different as to the spectator, but in
itself remaining unaltered, will produce in him a sensation of different
colours, or shades of colour, now blue, now green, now brown, now black,
and so on. This is the doctrine of Newton, as well as of Locke.

It follows that, if there were no percipient being to receive these
sensations, there would be no heat or cold, no taste, no smell, no
sound, and no colour.

Aware of this difference between our sensations in certain cases and
the causes of these sensations, Locke has divided the qualities of
substances in the material universe into primary and secondary, the
sensations we receive of the primary representing the actual qualities
of material substances, but the sensations we receive of what he calls
the secondary having no proper resemblance to the causes that produce
them.

Now, if we proceed in the spirit of severe analysis to examine the
primary qualities of matter, we shall not perhaps find so marked a
distinction between those and the secondary, as the statement of Locke
would have led us to imagine.

The Optics of Newton were published fourteen years later than Locke's
Essay concerning Human Understanding.

In endeavouring to account for the uninterrupted transmission of rays of
light through transparent substances, however hard they may be found to
be, Newton has these observations.

"Bodies are much more rare and porous, than is commonly believed.
Water is nineteen times lighter, and by consequence nineteen times
rarer, than gold; and gold is so rare, as very readily, and without the
least opposition, to transmit the magnetic effluvia, and easily to admit
quicksilver into its pores, and to let water pass through it. From all
which we may conclude, that gold has more pores than solid parts, and by
consequence that water has above forty times more pores than parts. And
he that shall find out an hypothesis, by which water may be so rare,
and yet not capable of compression by force, may doubtless, by the same
hypothesis, make gol