part of this girt squared and multiplied by the length gives the content.

If the tree be very irregular, girt it in several places equally distant from each other, and divide the sum of the girts by their number for a mean girt. Or, which is more correct, divide the tree into several lengths, and find the content of each part separately by the above rule.

Example: If a round piece of timber be 112 inches in circumference, or the quarter girt be 28 inches, and the length 22 feet, how many feet of timber are contained therein, by the customary and true methods?

If a piece of square timber be 32 inches square at the greater end, and 12 inches square at the lesser (or, the same thing, the greater girt in the middle be 22 inches), and the length 26 feet, how many feet of timber are contained therein, both by the customary and true method?

T

What is the solid content of a wall whose length is 112 feet 9 inches, its height 15 feet 6 inches, and thickness 3 ft.?

What is the sold content of a wall whose length is 346 feet 6 inches, height 18 feet 6 inches, and thickness 2 feet 6 inches? Answer, 16025 62 feet.

If a pane of glass be 4 feet 10 inches long and 2 feet 3 inches broad, how many feet of glass are in that pane?

If there be 10 panes of glass, each 5 feet 4 inches long, and 2 feet 6 inches broad, how many feet of glass are contained in them? Answer, 137 feet 2 inches.

If a gravel walk is to be made 400 yards in length, 7 feet in width, and 6 inches in depth, how many cubic yards of gravel should be ordered for the purpose?

400 yards
3

divide by 27) 42000 (155 yards

the solid feet in a yard 27

150

135

150

135

15 feet. Answer, 155 yards and 15 ft.

Physical Geography.

Mr. B. The equalization of temperature by the atmosphere is a subject worthy of our attention this evening. Immediately that the air becomes heated by contact with the heated earth it ascends by reason of the greater density of the cold air about it, but after a short ascent it attains a region where the surrounding medium-although it may be colder -is but equally dense. There, then, its ascent terminates.

It is there-instead of at the surface of the atmosphere-that it begins to spread itself, and there it determines its current. Along this region comparatively near to the earth's surface it distributes its heat, radiating part, and propagating the rest by contact-bearing it in a current, at first downwards to some point, perhaps far removed from that where it arose, and disturbing the equilibrium of the subjacent air wherever it passes.

By the laws of hydrodynamics (that branch of natural philosophy which treats of the phenomena of water and other fluids) the motion of this current above necessarily brings about a motion of the air beneath it; a result which is favoured by its continual tendency as it cools, to descend.

Moreover the original displacement of this mass of air is brought about by a motion of the air around it, and the motion of this air supposes that of some other mass of air adjacent to it, that of a third, and so on. Thus every variation in the temperature of the lower air propagates a series of displacements of its mass along the earth's surface, and of currents in a region more or less elevated above it. are the winds.

These

Higher than the regions of the winds, the mass of the atmosphere is comparatively untroubled-they rage at the bottom of that mighty ocean of air, and do not ruffle its surface. By the marvellous wisdom of this disposition the heat which the winds bear with them is made not to waste itself in the higher atmosphere, but to cherish the earth.

Son. It has been calculated that a current of air flowing over a warmer surface, whether of land or water, becomes in the space of an hour penetrated with the same temperature as the surface over which it travels to the depth of eighty feet. Our easterly winds present a remarkable example of the circumstances under which the temperature of one region is borne to another. In the spring and early summer their direction is from the east and north-east, and, coming from the cold steppes of Siberia over the northern limit of the great central plain of Europe, they reach us chilled and frozen. In the autumn their direction is south-east and they traverse the sultry region of Arabia and Asia Minor; they are then hot and thirsty.

Mr. B. The winds carry the heat from the torrid zone not only as do the waters of the ocean to the shores of northern and temperate regions, but over the broad surface of the land -over hill and valley, through the deep forest into the matted foliage of the trees, and amongst the tangled grass; and no stunted shrub, or hidden flower or weed is too humble to be beneath their ministry.

Our great object is to trace effects to their causes, which you must always bear in mind. To give you an illustration, when the torrent descends from the mountains, we go for the immediate cause of it to the rain, which rain is supplied by the clouds, which clouds are formed of vapours, which vapours are made buoyant by the air and raised by the light, which light is sent forth by the action of the orb of the sun, and when we have got thus far we have reached what appears to us to be the first mover in the visible world.

Son. That system, although it may be the best, confines the question to such a small compass that it requires strong reasoning powers to trace effects, through all their ramifications, to their causes.

Mr. B. I think that you mistake my meaning, and have used the words "through all their ramifications," high sounding words by the bye, as if I had not allowed free scope, (to continue your metaphor,) for such divisions of the main branches of the subject as may be necessary to illustrate the stem or principal part. But as I see that I have carried you out of your depth (although I may adopt a similar course, when you are better acquainted with the subjects, in some of my future lessons), and that you might confound the effect with the cause, as Baron Humboldt tells us. "You would look in vain for water serpents," said an old Indian of Javita to us, gravely, "where there are not marshes, because the water collects no more when you imprudently kill the serpents that attract it." I will now return to our usual form of a familiar explanation of the subject on hand.

'You are, no doubt, aware that all the water which sinks into the ground either as rain, hail, or snow, in the course of time rises out of it again. It is the same water which successively forms seas, rivers, springs, clouds, rain, and sometimes hail, snow, and ice. If you will take the trouble of following it through these various changes, you will understand why the earth is not yet drowned by the quantity of water which has fallen upon it since its creation, and you will even be convinced that it does not contain a single drop more water now than it did at that period.

Let us consider how the clouds were originally formed. When the first rays of the sun warmed the surface of the earth, the heat, by separating the particles of water, rendered them lighter than the air. This, you know, is the case with steam or vapour. When lighter than the air it will naturally rise, and when this watery vapour is exhaled, it is dissolved by the air-that is, sub-divided into such minute particles as to be invisible.

Journeyman. How then does it form clouds?