GUNNERY.

IT has been ascertained by experiment that the velocity of the ball projected from a gun varies as the square root of the charge directly, and as the square root of the weight of the ball reciprocally.-Hutton.

The same author furnishes the following practical rules:

To find the Velocity of any Shot or Shell.

RULE. As the square root of the weight of the shot is to the square root of the weight of treble the weight of the powder, both taken in pounds, so is 1600 to the velocity in feet per second.

EXAMPLE.-What is the velocity of a shot of 196 lbs., projected with a charge of 9 lbs. of powder?

14 5.2 1600 594, Ans.

When the Range for one Charge is given, to find the Range for another Charge, or the Charge for another Range.

RULE. The ranges have the same proportion as the charges; that is, as one range is to its charge, so is any other range to its charge, the elevation of the piece being the same in both cases.

EXAMPLE.--If, with a charge of 9 lbs. of powder, a shot range 4000 feet, how far will a charge of 63 lbs. project the same shot at the same elevation?

96.75 4000: 3000, Ans.

Given the Range for one Elevation, to find the Range at another Elevation.

RULE. As the sine of double the first elevation is to its range, so is the sine of double another elevation to its range.

EXAMPLE. If a shot range 1000 yards when projected at an clevation of 45°, how far will it range when the elevation is 30° 16', the charge of powder being the same?

Sine of 30° 16'X2 87064.

Then, as 100000 1000: : 87064: 870.64, Ans.

EXAMPLE. The range of a shell at 45° elevation being 3750 feet, at what elevation must a gun be set for a shell to strike an object at the distance of 2810 feet with the same charge of powder ?

As 3750 100000 :: 2810: 74934, the sine for double the elevation of 24o 16', or of 65° 44′, Ans.

R

FRICTION.

EXPERIMENTS upon the effect of this branch of mechanical science are as yet not of such a nature as to furnish deductions for very satisfactory rules.

The friction of planed woods and polished metals, without lubrication, upon one another, is about of the pressure.

Friction does not increase with the increase of the rubbing surfaces.

The friction of metals is nearly constant; that of woods seems to increase with action.

The friction of a cylinder rolling upon a plane is as the pressure, and inversely as its diameter.

The friction of wheels is as the diameter of their axes directly, and as the diameter of the wheel inversely.

Friction is at a maximum after a state of rest; the addition is as the fifth root of the time.

The following are the results of some experiments, without lubrication, as given by Adcock:

FRICTION AFTER A STATE OF REST.

1

1

At a maximum, oak on oak, to of the weight, according to the magnitude

2.28 2.39
1

1

of the surface; for oak on pine,; for pine on pine, for elm on elm, 2.18 of the weight, the fibres moving longitudinally.

1.78

When they cross at right angles, the friction of oak is

1

1

for iron on iron, 5; for iron on brass,, the surfaces well polished; but when

For iron on copper, with tallow, the friction is of the weight; when olive il is used, the friction is increased to.

The Friction on a level Railroad of a Locomotive is about; that is, an engine weighing 10 tons has a tractive power of 2 tons by the friction of the surfaces of its wheels upon the rails.

FRICTION OF BODIES IN MOTION,

Without Lubrication.

When the surfaces are large, the friction increases with velocity.

1

9.5'

For a pressure of from 100 to 4000 lbs. on a square foot, for oak on oak, the friction is about besides a resistance of about 13 lbs. for each square foot, independent of the pressure. When the surface is very small, the friction is somewhat diminished. For oak on pine, the friction is ; for pine on pine, 6.3

1

13'

1

copper on wood, which is much increased by an increase of the velocity; for iron on iron,

for iron on copper, after much use, at all velocities.

Where the unctuous matter is interposed between the surfaces, the hardest were found to diminish the friction most where the weight was great. Tallow, applied between oak, reduced the friction to of the pressure. When the surfaces are very small, tallow loses its effect, and the friction is increased to; the adhesion was about 7 lbs. per square foot.

28

With tallow between iron on oak, the friction is; with brass on oak, for iron on iron, the friction is, adhesion 1 lb. for 15 square inches; on copper, adhesion 1 lb. for 13 square inches; with soft grease or oil, the friction of iron on copper and brass was and .

On the whole, in most machines, of the pressure is a fair estimate of the friction.

FRICTION ON AXES.

For axes of iron on copper, where the velocity was small, the friction being always a little less than for plane surfaces. An axis of iron, with a pulley of gua facum, gave, with tallow, 20

FRICTION AND RIGIDITY OF CORDAGE.

Wet ropes, if small, are a little more flexible than dry; if large, a little less flexi ble. Tarred ropes are stiffer by about, and in cold weather somewhat more.

FRICTION OF PIVOTS.

When the angle of the summit of the pivot is about 180 or 200, the friction for garnet is Too to Too; agate, i rock crystal,

1

1

glass,

and steel (tempered). At an angle of 450 the friction is much reduced, and the friction of agate and steel are then nearly equal.

NOTES.-In general, friction is increased in the ratio of the weight.

Between woods, the friction is less when the grains cross each other than when they are placed in the same direction.

Friction is greater between surfaces of the same kind than between surfaces of different kinds.

The best Lubricators are, and in the following order: Tallow; Soft Soap, Lard, Oil, and Black-lead.

HEAT.

HEAT, in the ordinary application of the word, signifies, or, rather, implies the sensation experienced upon touching a body hotter, or of a higher temperature than the part or parts which we bring into contact with it; in another sense, it is used to express the cause of that sensation.

To avoid any ambiguity that may arise from the use of the same expression, it is usual and proper to employ the word Caloric to signify the principle or cause of the sensation of heat.

CALORIC is usually treated of as a material substance, though its claims to this distinction are not decided; the strongest argument in favour of this position is that of its power of radiation. On touching a hot body, caloric passes from it, and excites the feeling of warmth; when we touch a body having a lower temperature than our hand, caloric passes from the hand to it, and thus arises the sensation of cold.

COMMUNICATION OF CALORIC.

Caloric passes through different bodies with different degrees of velocity. This has led to the division of bodies into conductors and non-conductors of caloric; the former includes such as metals, which allow caloric to pass freely through their substance, and the latter comprises those that do not give an easy passage to it, such as stones, glass, wood, charcoal, &c.

TABLE of the relative Conducting Power of different Bodies.

RADIATION OF CALORIC.

When heated bodies are exposed to the air, they lose portions of their heat, by projection in right lines into space, from all parts of their surface.

Bodies which radiate heat best absorb it best.

Radiation is affected by the nature of the surface of the body; thus, black and rough surfaces radiate and absorb more heat than light and polished surfaces.

TABLE of the Radiating Power of different Bodies.

REFLECTION OF CALORIC is the reverse of Radiation, and the one increases as the other diminishes.

SPECIFIC CALORIC.

SPECIFIC CALORIC is that which is absorbed by different bodies of equal weights or volumes when their temperature is equal, based upon the law, acknowledged as universal, that similar quantities of different bodies require unequal quantities of caloric at any given temperature. Dr. Black termed this, capacity for caloric; but as this term was supposed to be suggested by the idea that the caloric present in any substance is contained in its pores, and, consequently, the capacities of bodies for caloric would be inversely as their densities; and such not being the case, this word is apt to give an incorrect notion, unless it is remembered that it is but an expression of fact, and not of cause; and to avoid error, the word specific was proposed, and is now very generally adopted.

It is important to know the relative specific caloric of bodies. The most convenient method of discovering it is by mixing different substances together at different temperatures, and noting the temperature of the mixture; and by experiments it appears that the same quantity of caloric imparts twice as high a temperature to mercury as to an equal quantity of water; thus, when water at 1000 and mercury at 400 are mixed together, the mixture will be at 800, the 200 lost by the water causing a rise of 400 in the mercury; and when weights are substituted for measures, the fact is strikingly illustrated; for instance, on mixing a pound of mercury at 400 with a pound of water at 1600, a thermometer placed in it will stand at 1550. Thus it appears that the same quantity of caloric imparts twice as high a temperature to mercury as to an equal volume of water, and that the heat which gives 50 to water will raise an equal weight of mercury 1150, being the ratio of 1 to 23. Hence, if equal quantities of caloric be added to equal weights of water and mercury, their temperatures will be expressed in relation to each other by the numbers 1 and 23; or, in order to increase the temperature of equal weights of those substances to the same extent, the water will require 23 times as much caloric as the mercury.

The rule for finding by calculation, combined with experiment, the relative capacities of different bodies, is this:

Multiply the weight of each body by the number of degrees lost or gained by the mixture, and the capacities of the bodies will be inversely as the products.

Or, if the bodies be mingled in unequal quantities, the capacities of the bodies will be reciprocally as the quantities of matter, multiplied into their respective changes of temperature.

The general facts respecting specific caloric are as follows:

1. Every substance has a specific heat peculiar to itself, whence a change of composition will be attended by a change of capacity for caloric.