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The heat of the fire not being sufficient to cause all the carbon of the fuel to combine with oxygen, the combustion is, as it were, incomplete — the uncombined carbon rises in the shape of smoke, and is partly deposited on the sides of the chimney, and is collected for manuring our lands, and again used up for vegetable life; that part of it which ascends into the atmosphere is washed down by the rain, and so feeds the plants again
How beautiful to watch the ascent of the smoke on a calm summer's evening — sometimes ascending merrily, denoting fine weather, at another descending the moment it has escaped from the chimney; ascending because the specific gravity of the air is greater than that of the smoke; standing still, and in a sort of stable equilibrium on a calm evening, when the stratum of air in which it is floating is of the same specific gravity as itself; and descending when the specific gravity of the air is less than that of the smoke!
Here we see, in this apparent destruction of vegetable matter, that nothing is lost; the gaseous part which went up the chimney, and which forms a very great proportion of the whole, returns again to nourish vegetable and animal life; the ashes which remain, and contain the inorganic part of the fuel, are spread upon the ground to be dissolved through the agency of water and of the atmosphere, and so carried into the roots for the nourishment and support of fresh vegetable matter. Not the slightest particle is lost, and if all the products of the combustion were collected the water, carbonic acid, smoke, ashes and weighed, their weight would be found greater than that of the fuel, having been increased by the oxygen taken from the atmosphere during the combustion.
The flame of a candle might be the subject of two or three conversational lectures of this kind - showing the way in which the tallow or wax, when reduced into a fluid state by heat, ascended by capillary attraction up the wick, a length of which between the candle and the flame will be seen to be moistened with it; a higher degree of temperature changes this out of a fluid into a gaseous state, consisting of the different elements of the substance of the candle, one of which, hydrogen, ignites, the oxygen of the atmosphere supporting the flame, and the carbon, another element, ascending in the flame and being heated, increases the quantity of light. The products of this combustion, water and carbonic acid, may be collected by placing a funnel-shaped glass tube, with the larger end over the flame of the candle, and the smaller one bent and communicating with a glass cylinder kept cool, in passing into which the watery vapour arising from the flame would be deposited, and the carbonic acid passing on might be collected by an apparatus properly arranged at the other end of the cylinder, and then tested.
It has been found that the water produced by the burning of a candle is nearly equal in weight to that of a candle consumed; the collected products would be greater than this weight, but it will at once be seen that the oxygen of the atmosphere consumed explains this:-- the gas collected when properly tested will be shown to be carbonic acid.
That the vapour arising from the burning of a candle or a jet of hydrogen contains a great deal of water is easily shown, by holding a cold glass in such a direction that the ascending vapour may pass into it—the glass immediately becomes dim and wet—the same may be shown by holding a cold glass over a burning piece of cotton- of paper — or a splinter of wood.
Reason why the glass should be cold.
Again, that metals, such as lead, iron, etc., in a minute state of division, are much more inflammable than tallow, oil, fat, etc., or even than gunpowder, taking fire at the temperature of the atmosphere-sodium and potassium igniting the moment they come in contact with water or with ice—and if spirits of wine in a saucer or similar vessel be set on fire, iron filings thrown on the flame will burn and fall into the saucer, when they can be examined and will be found oxydised, but grains of gunpowder thrown into the
Tallow, oil, and fat will not ignite. flame in the same way require to be heated up to a certain point, when they readily burn, but must wait to be artificially heated before they do so—how beautiful this provision in order that they may be turned to the purposes of mankind - lighting their dwellings --enabling them to read-to work; -- how important all this to civilized life! --- and while we consider all these things “ do not let us forget Him who made them.”
In giving a short conversational lecture on birds, for instance, the teacher might speak of the way in which they build their nests — whether in trees or on the ground—the greater degree of skill shown by some in doing this, than by others - but that all birds of the same kind build in the same way that a bird builds its nest by instinct - man builds a house from reason, improves and profits from what others have done in that way before him— but that birds build now as they always have done, etc.
The striking difference of the state of their young, when hatched and leaving the egr--the chickens of the barndoor fowl, and of others of that class, will run about, and seek their own food, the moment they leave the egg-want but little assistance from the parent birds—that of the mother alone for a short time being quite sufficient, and the care of the male bird is not wanted in assisting to bring up a brood of chickens — the same with the duck —young ducks take to the water, and look out for themselves immediately.
Others again, such as hirds of prey, the eagle, the hawk — all our small birds—the young of these, after leaving the shell, are in a helpless state for some weeks, and depend entirely for support upon the parent birds, and require the assistance of both, in order to find a sufficient supply of food: these are always found in pairs, and want the assistance of both the parent birds to bring them up.
Then the structure of the bones—being hollow tubes, and full of air-cells—caused by little, strengthening, bony processes, which go from one side of the hollow tube to the other—(this would be seen by splitting the bones of fowls)-the outside bony substance of the tube being thickest at the extremities, where strength is wanted— all this required for the purposes of flight; but in the bones of animals moving on the ground, these hollow parts of the bone are filled with marrow-fewest air-cells in the bones of those birds whose habits do not require long flight, etc. The mechanical structure of the wing --- the pinion-bone moving in order to stretch out the feathers in the same plane with the one to which it is attached --if it admitted of an up-and-down motion out of that plane, the wing would be much less strong, and a much greater muscular power required to produce the same effect in flight, etc.
Again, on fish for instance—some breathing by means of gills, so as to get at the oxygen contained in the air of the water, all water containing air, it being necessary to the life of fish. Air contained in water being richer in oxygen by about 25 per cent. than the air of the atmosphere-this is important to fishes - although culd-blooded animals do not require by any means the same amount of oxygen in a given time as hot-blooded ones of the same size -perhaps not more than 31. th.
Some fish, such as the whale, etc., breathe by means of lungs, and take in air, for which purpose they are obliged to come up to the surface of the water.
All air-breathing fishes have a broad flat tail-à horizontal tail, giving them a mechanical advantage in rising to the surface — fishes breathing through the gills have the tail vertical, perpendicular to the water in which they float
thus to propel them forward and direct their motionsome fish, gelatinous masses, breathe at all points of their surface.
One reason why some fish live longer than others out of water, seems to arise from their having a different kind of gill, one which retains a quantity of water, and so long as they can get oxygen from this water in the gills they continue to live.
Any one wishing to give short conversational lectures of this kind, if unaccustomed to do so, will find it of assistance to read from a book any striking passage which may occur, or which he may happen to meet with in his own reading, embracing facts easy of illustration, or describing the manners and customs of other nations; such, for instance, as the following:
“ Certain insects can run about on the surface of the water. They have brushy feet, which occupy à considerable surface, and if their steps be viewed with a magnifying glass, the surface of the water is seen depressed all around, resembling the footsteps of a man walking on feather-beds. This is owing to a repulsion between the brush and the water. A common fly cannot walk in this manner on water. Its feet are wetted, because they attract the water instead of repelling it. A steel needle, slightly greased, will lie on the surface of water, make an impression as a great bar would make on a feather-bed, and its weight is less than that of the displaced water. A dewdrop lies on the leaves of plants, without touching them mathematically, as is plain from the extreme brilliancy of the reflection at the posterior surface; nay, it may sometimes be observed, that the drops of rain lie on the surface of water, and roll about on it, like balls on a table. Yet all these substances can be wetted ; that is, water can be applied to them at such distances that they attract it.”
How easy to make interesting remarks un a passage like this, and how delighted children are to hare the philosophy of such things as flies walking on water, or needles floating on it, explained to them — or of any facts which come frequently under their own observation.
I have been very much pleased with the interest I have found the children would take in having any graphic passage read to them, descriptive of the modes of life, occupations, etc., of other nations or people, and have occasionally read passages of that kind myself, and am in the habit of pointing out such to the school teachers to read. I will instance the following: while reading “Hochelaga,” a description of Canadian life, the following passages occurred to me as giving a lively picture of what it is their object to describe, and one quite coming home to the minds and capacities of children. I took the book into the school, and read them, and the interest with which they were listened to, with a few observations I made myself, would have convinced any one of the usefulness of this suggestion. On an occasion like this, the teacher would, as an economy of time, unite all the intelligent part of his school.
For about three weeks after Christmas, immense numbers of little fish, about four inches in length, called “tommy-cods,” come up the St. Lawrence and St. Charles: for the purpose of catching these, long narrow holes are