upon its cultivators, to add new fields to its dominions.  Yet, does this continually and rapidly increasing power, instead of giving us any reason to anticipate the exhaustion of so fertile a field, place us at each advance, on some higher eminence, from which the mind contemplates the past, and feels irresistibly convinced, that the whole, already gained, bears a constantly diminishing ratio to that which is contained within the still more rapidly expanding horizon of our knowledge.

464.  But, if the knowledge of the chemical and physical properties of the bodies which surround us, as well as our imperfect acquaintance with the less tangible elements, light, electricity, and heat, which mysteriously modify or change their combinations, concur to convince us of the same fact; we must remember that another and a higher science, itself still more boundless, is also advancing with a giant’s stride, and having grasped the mightier masses of the universe, and reduced their wanderings to laws, has given to us in its own condensed language, expressions, which are to the past as history, to the future as prophecy.  It is the same science which is now preparing its fetters for the minutest atoms that nature has created:  already it has nearly chained the ethereal fluid, and bound in one harmonious system all the intricate and splendid phenomena of light.  It is the science of calculation—­which becomes continually more necessary at each step of our progress, and which must ultimately govern the whole of the applications of science to the arts of life.

465.  But perhaps a doubt may arise in the mind, whilst contemplating the continually increasing field of human knowledge, that the weak arm of man may want the physical force required to render that knowledge available.  The experience of the past, has stamped with the indelible character of truth, the maxim, that knowledge is power.  It not merely gives to its votaries control over the mental faculties of their species, but is itself the generator of physical force.  The discovery of the expansive power of steam, its condensation, and the doctrine of latent heat, has already added to the population of this small island, millions of hands.  But the source of this power is not without limit, and the coal-mines of the world may ultimately be exhausted.  Without adverting to the theory, that new deposits of that mineral are not accumulating under the sea, at the estuaries of some of our larger rivers; without anticipating the application of other fluids requiring a less supply of caloric than water—­we may remark that the sea itself offers a perennial source of power hitherto almost unapplied.  The tides, twice in each day, raise a vast mass of water, which might be made available for driving machinery.  But supposing heat still to remain necessary, when the exhausted state of our coal fields renders it expensive:  long before that period arrives, other methods will probably have been invented for producing it.  In some districts, there are springs of hot water, which have flowed for centuries unchanged in temperature.  In many parts of the island of Ischia, by deepening the sources of the hot springs only a few feet, the water boils; and there can be little doubt that, by boring a short distance, steam of high pressure would issue from the orifice.(5*)