, and we
should look back upon our past state as upon a blind chrysalid form of
existence in which we had been unconscious of all this new wealth of
perception.

It cannot be too clearly and strongly insisted on and brought home to
every mind, that the mode in which the universe strikes us, our view of
the universe, our whole idea of matter, and force, and other worlds, and
even of consciousness, depends upon the particular set of sense-organs
with which we, as men, happen to be endowed. The senses of force, of
motion, of sound, of light, of touch, of heat, of taste, and of
smell--these we have, and these are the things we primarily know. All
else is inference founded upon these sensations. So the world appears to
us. But given other sense-organs, and it might appear quite otherwise.
What it is actually and truly like, therefore, is quite and for ever
beyond us--so long as we are finite beings.

Without eyes, astronomy would be non-existent. Light it is which conveys
all the information we possess, or, as it would seem, ever can possess,
concerning the outer and greater universe in which this small world
forms a speck. Light is the channel, the messenger of information; our
eyes, aided by telescopes, spectroscopes, and many other "scopes" that
may yet be invented, are the means by which we read the information that
light brings.

Light travels from the stars to our eyes: does it come instantaneously?
or does it loiter by the way? for if it lingers it is not bringing us
information properly up to date--it is only telling us what the state of
affairs was when it started on its long journey.

Now, it is evidently a matter of interest to us whether we see the sun
as he is now, or only as he was some three hundred years ago. If the
information came by express train it would be three hundred years behind
date, and the sun might have gone out in the reign of Queen Anne without
our being as yet any the wiser. The question, therefore, "At what rate
does our messenger travel?" is evidently one of great interest for
astronomers, and many have been the attempts made to solve it. Very
likely the ancient Greeks pondered over this question, but the earliest
writer known to me who seriously discussed the question is Galileo. He
suggests a rough experimental means of attacking it. First of all, it
plainly comes quicker than sound. This can be perceived by merely
watching distant hammering, or by noticing that the flash of a pistol i