80 
equally confident of my ability to do justice to so noble 
a theme. 
The lecture bears the somewhat poetic title of “A 
Glimpse through the Corridors of Time.’ A poetic title 
has been chosen, because if I can properly exhibit the 
subject you will see that it appeals powerfully to the 
imagination as well as to the reason. I shall invite you 
to use your imagination to aid in looking back into the 
very remotest recesses of antiquity. And when I speak 
of antiquity I do not mean the paltry centuries with 
which our historians have to deal. The ancient days to 
which I refer are vastly anterior to those of the “grand 
old masters” and those of the “‘bards sublime.’’ Nor do 
we even allude tc the thousands of years which have 
elapsed since Babylon and Nineveh were splendid and 
populous cities Even the noble pyramids of Egypt are 
but of yesterday when compared with the zons of years 
which must pass before our review. 
The most ancient human monuments that now exist 
cannot, | suppose, be more than a few thousand years 
old. Five thousand years nearly exhausts all historical 
time. Ten thousand years certainly does. Though 
we have no earlier historical record, yet other records 
are not wanting. Geology tells us that ten thou- 
sand years is but a mere moment in the span of the 
earth’s history. We learn from geology that even the 
career of man himself has lasted far more than ten thou- 
sand years. Yet man is but the latest addition to the 
succession of life on the earth. For the chronology of the 
earlier epochs of the earth’s history we require majestic 
units to give adequate expression to our dates. Thou- 
sands of years are not sufficient, nor tens of thousands, 
nor hundreds of thousands. The course of geological 
time is to be reckoned in millions of years. 
The corridors of time through which I wish to give you 
a glimpse are these dignified millions. Yet our retrospect 
will only extend to a certain definite epoch in the past 
history of our earth. We speak of nothing anterior to 
the time when our earth assumed the dignity of maternity, 
and brought forth its first and only child. We shall trace 
the development of that child which, though millions of 
years old, is still in dependence on its parent. We shall 
describe the influence of the parent over the child and 
the not less remarkable reaction of the child upon the 
parent. We shall foreshadow the destiny which still 
awaits the mother and child when millions of years shall 
have elapsed. 
At the time of its birth the earth was not as we see it 
now, clothed with vegetation and teeming with animal 
life. It was a huge inorganic mass, too hot for life, per- 
haps hot enough to be soft or viscid, if not actually 
molten. The offspring was what might be expected 
from such a parent. It was also a rude inorganic mass. 
Time has wrought wondrous changes in both parent and 
child. Time has transformed the earth into an abode of 
organic life. It has transformed the earth’s offspring into 
our silvery moon. 
{t will be my duty to sketch for you the manner in 
which these changes have been brought about. To a 
great extent we can do this with no hesitating steps, we 
are guided by a light which cannot deceive. It is the 
light of mathematical reasoning. These discoveries are 
of an astronomical character, but they have not been 
made by telescopes. They have been made by diligent 
labours of the most abstruse kind. The mathematical 
astronomer sits at his desk, and not in an observatory. 
He has in his hand a pen and not a telescope. Before 
him lies a sheet of paperand not the starry heavens. He 
is no doubt furnished’with a few facts from observation. 
it is his province to interpret those facts, to inform them 
with life, and to infer the unknown from the known. It 
is thus discoveries are made which are the sublimest 
efforts of human genius. 
The argument on which I invite you to follow me is 
NATURE 
[Nov. 24, 188 I 
founded on a very simple matter. Many of those present 
go every summer to the sea-side. Those who do so are 
well acquainted with the daily ebb and flow which we call 
the tides. Even the children with their spades and 
buckets know how the flowing tide will fill their moats 
dug in the sand and inundate their mimic castles. 
In the ebb and flow of the tide we have a mechanical 
engine of mighty power. I hope this evening to point 
out the wonderful effect which tides have had on the 
earth in times past, as well as the effect they will exercise 
in the future. It is the tides which are to reveal to us a 
glimpse through the Corridors of Time. 
The cause of the ebb and flow of the tide has long 
ceased to be a mystery. In the earliest times it was 
noticed that the tides were connected with the moon. 
Pliny and Aristotle both refer to the alliance between the 
tides and the age of the moon. It is well known that the 
tides on our coasts sometimes rise to an unusual height. 
Those who dwell on low ground adjoining tidal rivers are 
painfully aware of this fact by the floods which are often 
produced. Such occurrences generally take place at the 
time of new moon orof full moon. At first quarter or last 
quarter the tides are even below the usual height. A 
fisherman who has to regulate his movements by the 
tides will know full well that at certain times the tides 
rise higher and fall lower than at other times. He brings 
his boat out on the falling tide, he brings it back on the 
rising tide, and when making the harbour after a night's 
fishing, it would be natural to hear him say ‘‘ Oh, we shall 
run in easily this morning, there is a strong tide, the 
moon was full last night.” Or if he had to cross a 
dangerous bank he would soon learn the difference 
between the spring tide and the neap. Fishermen are 
not much addicted to abstract reasoning. For many 
centuries, perhaps indeed for thousands of years, ob- 
servant men might have known that the moon and the 
tides were connected. But they did not know any reason 
why this connection should exist. I daresay they did not 
even know whether the moon was the cause of the tides 
or the tides the cause of the moon. 
Nor is it easy to explain the tides. We were all taught 
that the moon makes the tides. Yet I can imagine an 
objector to say, If the moon makes the tides, why does it 
give Bristol a splendid tide of 4o feet, while London is 
put off with only 18? The true answer is that the height of 
the tide is largely affected by local circumstances, by the 
outline of the coasts, by estuaries and channels. It is 
even affected to some extent by the wind. Into such 
details, however, I do not now enter : all I require is that 
you shall admit that the moon causes the tides, and that 
the tides cause currents. In some few places the currents 
caused by the tides are made to do useful work. A large 
reservoir is filled by the rising tide, and as the water 
enters it turns a water-wheel. On the ebbing tide the 
water flows out of the reservoir, and again gives motion 
to a water-wheel. There is here a source ot power, but 
itis only in very exceptional circumstances that such a 
contrivance can be worked economically. Sir W. Thom- 
son, in his address to Section A of the British Association 
at York, went into this question in its commercial aspect. 
At present, however, we may say that the power of the tides 
is as much wasted as is the power of Niagara. Perhaps 
when coal becomes more scarce, and when the means of 
distributing power by electricity are more developed, the 
tides and the great waterfalls will be utiiised; but that 
day will not be reached while coal is only a few shillings 
a ton. 
Though we have not yet put the tides into harness, yet 
tides are not idle. Work they will do, whether useful or 
not. In some places the tidal currents are scouring out 
river-channels ; in others they are moving sandbanks. 
From a scientific point of view the work done by the 
tides is of unspeakable importance. To realise the im- 
portance, let us ask the question, Whence is this energy 
