spread out, on their table-summits, cool and agreeable cli

mates.

We remark, in this law of physics, an admirable foresight of nature. If the air had not afforded a free passage to heat without becoming warm itself from the transit, if heat had diffused warmth through the extent of the sky, the glaciers of the Alps, of the Pyrennees, the Cordilleras, and the Himalaya, had not existed. No river, no stream, had flowed from the mountains. No changes of temperature had given birth to condensation and rains, and the universe would have been a ruin.

Yet this same inequality of temperature has inspired certain philosophers with bitter complaints, and even the denial of Providence. One half the globe, according to them, is scorched by the sun, and the other half buried under ice. A superficial view of things saddens and discourages, and smatterers become unbelievers. But, in proportion as we profoundly investigate the phenomena of nature, the mind changes to admiration of the wisdom and foresight of Nature, and raises adoring conceptions of its Author.

For example, the fires of the equator, and the ices of the poles, have been alike the foundation of a charge against Providence. All beings below would perish, however, if this same Providence had not arranged things as they are. The poles in chilling the air, and the torrid zone in heating it, are the cause of the different currents which preserve the purity and the freshness of the air. Without them, no wind would have brought us clouds and rains; no zephyrs would have swelled the buds. Our harvests would have failed, but for the sources of storms placed at the extremities of the world. It is at the poles, and under the equator, that are generated those mighty causes which take up the evaporated waters from the bosom of the ocean, and transport them to the mountains in the interior of continents, to be condensed in rains, to descend in mountain-torrents, to meander in rills, to roll in rivers, to water whole countries, and to return whence they sprung.

Specious objections vanish before the most simple and

obvious reflections. We have only to cast a considerate eye upon creation, to be convinced that a divine harmony, a celestial foresight, presides over all these seeming inconsistencies. Apparent disorder is unknown order; and, in every accusation against the Author of nature, time, study, and experience, will unfold an act of ignorance as well as impiety.

One word respecting the central fires, an invention of the ancient philosophers, honored by being adopted by some of the moderns, will close this lecture,

They called by the name of central fire, the interior warmth of the globe. This warmth serves to explain the vegetation that takes place under the snow, the boiling fountains of Spitzbergen, the astonishing hot jet d'eau of Geyser, the high temperature of deep mines, and, generally, the volcanic character of whole chains of mountains.

According to Whiston, the earth before the deluge was much more populous and fertile than at present. Human life, too, was longer in proportion to the greater internal warmth, or central fire. But this same fire, in augmenting the strength of the human body, unhappily mounted into the head, and turned the brain. Men became proud of deceiving innocence, and of killing their friends in duels. They boasted of not believing in a God, and wrote admirable books about the power of nothing to create something. The animals even, with the exception of fishes that inhabit a cold element, felt the effects of this mischievous influence, became criminal and deserving of death. This universal death was inflicted, according to our philosopher, one Friday, on the twenty-eighth of November, by an unhappy meeting between the earth and the tail of a comet.

LECTURE XXXI.

CALORIC.

In those ancient days so much boasted by the moderns, when the philosophers were content with believing that the sun was a fiery cloud of a foot in diameter, or at most no larger than Peloponnesus; one of the most renowned sages, in the midst of the gardens of the Academy, was theorizing with great confidence and power. He was explaining, in brief terms, how all the worlds which roll in space, were created. A young disciple of Plato, accustomed to reason by proposing questions, as is the fashion with some of his modern disciples in a part of our country, thus addressed him : -'O sage! condescend to enlighten me upon these mysteries; how it happens, that the rays falling upon wax causes it to drop in threads of gold, while the same heat, applied to moist clay, changes it to stone? Or that man, moving under the full ardor of these rays, is covered with sweat, while the same heat dries up the fountains and streams ? Or, that the same light reddens the rose, stripes the tulip, blanches the lily, and browns the shepherd girl? Whence is it that the same cause operates such opposite effects?' The disciple of Plato ceased ; and the sage world-builder not being able to resolve the questions of a scholar, touching. the most obvious matters of daily observation, retired overwhelmed with shame from the academy.

In these more fortunate days, we have in our ordinary schools young doctors of sixteen, and fair Euclids at twelve, who, standing at the black-board during an examination, are able at least to discourse learnedly upon these points of philosophy, if they cannot satisfactorily explain them.

The great agent of these seemingly contradictory results, is a subtile, invisible fluid, of which I have already spoken,

called caloric. The effect of the presence of this fluid to the perception of a sentient being, is warmth. It is supposed to expand bodies by penetrating between their molecules. In this way, a bar of red hot iron becomes perceptibly longer than when cold. A still greater quantity of caloric would have caused this bar to melt and flow, like a fluid. Whoever visits the mint will see gold and silver, by this action, become as liquid as water. Caloric, entering into the particles of water, dilates them first into steam, and then into invisible vapor. Remove this power, and the transparent fountains change to a substance like glass. To this element air owes its fluidity. The atmosphere itself would become a solid body, if caloric did not expand the molecules which compose it. It is affirmed in these days, that philosophers have succeeded in compressing air, so as to render it twice as dense as water.

Although caloric and light are frequently found in union, it is not uncommon to find them in separation. We have seen that sea-water, and many insects, offer us the brightest light without a particle of heat; and we can heat a great number of substances without rendering them luminous. It is natural to suppose, then, that caloric and light are two different bodies, which have a great analogy the one with the other, though many modern philosophers confound them.

The most remarkable property of caloric is to expand bodies; that is to say, to augment their volume in gliding between their molecules. This effect, as I remarked at the commencement of these lectures, is directly opposed to that of the attraction of aggregation, which draws the molecules of bodies towards one another. There is, therefore, a continual war between these two forces; and from this war results all the varied forms of matter, from the state of a solid to that of a liquid, and still further to that of an æriform fluid.

A certain quantity of caloric, added to a solid body, changes it to a fluid. If we add still more caloric, it separates the molecules of the fluid so far from each other, that their attraction of aggregation is entirely destroyed, and the liquid is transformed into vapor or steam.

When I touch a warm body, the caloric which is perpetually tending to an equilibrium, passes from this body into my hand. On the contrary, when I touch a cold body, the caloric passes from my hand into that body, and I experience a sensation of cold. To the property which caloric thus has to pass from one body to another, we owe the invention of the thermometer. The heat, in expanding the quicksilver, increases its volume, and causes it to ascend in a small cylindrical glass vessel, marked with circles at equal distances, called a graduated scale, by which the increase of the heat is noted.

There are bodies which the heat penetrates only with difficulty. They retain their caloric, and grant it a difficult passage. They are called bad conductors. On the contrary, bodies which give a free and easy passage to their caloric, are called good conductors. If you raise the wick of a lamp with a pin, the heat is immediately communicated to your hand. Metals are good conductors. You burn a match, on the contrary, until the flame almost touches your hand without giving you the sensation of heat. Wood is, therefore, a bad conductor.

A little girl went into the study of Mezerai, the celebrated historian, to get fire. Having forgotten to bring a vessel in which to carry the fire, she put some ashes in the bottom of her hand, and, to the great astonishment of the philosopher, put the burning coals upon the ashes, and carried off the fire in her hand. Experience had taught the child, that ashes were a bad conductor of heat.

The warmest bodies are bad conductors. Such a substance is a woollen dress. It keeps off the cold, not as some suppose, by imparting warmth, but in hindering the warmth of our bodies from escaping. Hence, when the air is warmer than our bodies, a woollen dress tends to keep us cool.

Most of the animals, by an admirable contrivance of the Creator, are covered with wool, fur, hair, feathers, all substances among the number of bad conductors. They are clothed by the hand of Providence exactly in conformity