enough to describe many more complicated combinations of mechanical powers. But, though so much has been said on the details of its structure and uses, the steam engine can still be made the subject of a book intended for the information and amusement of those who have nothing to do with its construction, and who I would shun those volumes of elaborate scientific matters which the mechanist so eagerly collects. If, however, it be remembered that its history could furnish a volume of anecdote and biographical notices of the many illustrious men connected with its manufacture and application, it will not be thought an undesirable topic for a volume addressed to general readers. Nor let it be supposed that the subject is one which is destitute of religious bearings. In the bestowal of this gift upon His intelligent creatures, we may clearly trace the benevolence of God; while in its discovery at a fitting period of the world's history, his providential care is no less clearly apparent. The selfishness, too, which has occasionally perverted an engine, meant to alleviate human toil, into an instrument for increasing it, opens to the thoughtful reader a vein of important reflection; illustrating, as it does, the corrupt principles of the human heart, and the necessity for their coun teraction by the gracious provisions of that gospel which is the sovereign remedy for all the ills, individual or social, of man's condition.

The reader would be deceived by the assertion

that the construction of the steam engine, in all its proportions and deteils, can be easily learned, or that the applicatior. of a few hours in studying the best books would enable him to master the subject. Still, principles can be laid down which may serve as the basis for more advanced studies, and explanations can be given which inay largely gratify the intelligent reader's thirst for information. Many are ignorant about the steam engine because they have had few opportunities of learning. Their inquiries have been met with answers unintelligible to them from the want of some preliminary knowledge, or from the teacher's ambiguity of expression. To this class the following pages will be well suited. Minute descriptions, mechanical details, scientific comparisons of one contrivance with another, would be altogether out of place, and will be avoided. A concise, but clear description of the causes and mode of action of the steam engine is all that can be attempted by the author, and all, it may reasonably be expected, that will be looked for by the reader.

WHAT THE ANCIENTS KNEW ABOUT STEAM, ETC. 11

CHAPTER I.

WHAT THE ANCIENTS KNEW ABOUT STEAM AND THE STEAM ENGINE.

To think more highly of ourselves than we ought to think is the fault of nations as well as of individuals. In no instance is this more clearly exhibited than in the exaggerated estimate so frequently made of the knowledge and wisdom of our age, by the assumption that all previous generations were absolutely ignorant. It is necessary we should fairly calculate the amount of our knowledge and the extent of our advantages, in order that we may be conscious of our responsibilities; but it may be doubted whether this is always best done by such comparisons as in complacent mood we are apt to indulge. The lack of documentary evidence is a strong impediment to a fair judgment of ancient learning and discovery. But in our estimate of what does remain we are liable to make erroneous deductions from misconception; for the philosophers of antiquity frequently communicated their knowledge in brief, sententious, emblematical language, which we misconstrue

from ignorance of their modes of thought and expression That the scientific information of the present day far exceeds that of any other age of which we have explicit records cannot be doubted, but this gives no authority for the common belief that every discovery of this and the last century was previously unknown. The closer the scientific annals of ancient Asiatic nations are examined, the more powerful is the conviction that many of the fundamental principles of natural science were discovered and applied by the more intelligent castes, and that this is not the first age in which curiosity has been excited, investigation active, and knowledge obtained. Nor is it difficult to understand how truths, once acquired, may have been subsequently lost. Desolating wars, the fall and dispersion of nations, the inroads of the powerful and barbarous upon the wise, the long pilgrimage and laborious settlement of colonists, are sufficient to account for the comparative destitution of science among the nations of antiquity, and especially among the Greeks and Romans, with whose history we are most familiar.

The Greeks as a nation were given to pleasure, and their high appreciation of works of imagination and metaphysical subtlety was an impediment to the prosecution of scientific researches. The character of the Athenians, the most polished and learned of this remarkable people, was well described by the apostle Paul, when, standing on Mars' Hiil, he addressed them"Ye men of Athens! I perceive that in all

things ye are too superstitious." Nor are their habits less pointedly described in that incidental allusion preceding the report of his oration "All the Athenians and strangers which were there spent their time in nothing else, but either to tell, or to hear some new thing." This was a bad soil for the growth of experimental philosophy, but there were some even among this people who possessed an amount of scientific knowledge which we should not in modern times have suspected, had the names and works of Euclid and Hero of Alexandria been lost. The former has left a treatise on geometry which is the text-book in all the schools and colleges of Europe, and the other a work on pneumatics, from which we learn that one hundred and twenty years before Christ, many of the properties of air and steam were understood, and attempts made to apply their mechanical force. Let us see what this Hero, the Alexandrian philosopher, knew about steam and steam engines :—

"When round medical glasses which have long slender necks," he says, "are to be filled with water, the air contained in them is sucked out, and the orifice closed with the finger; they are then inverted in water, and on removing the finger, the water is drawn up into the vacuous space, in contradiction to the usual law of fluids." From this description, which is not sufficiently explicit to inform us whether the tube was of that hairlike bore called capillary, or merely a tube of small dimensions, we learn