Things To Make Part 22

The post should be well painted, the top protected by a zinc disc laid under the top bracket, and the bottom, up to a point 6 inches above the ground level, protected by charring or by a coat of boiled tar, before the dial and the brackets for the vane rod to turn in are fastened on. A white dial and black arrow and letters will be most satisfactory against a dark background; and vice versa for a light background. The letters are of relatively little importance, as the position of the arrow will be sufficient indication.

It gives little trouble to affix to the top of the pole 4 arms, each carrying the initial of one of the cardinal points of the compa.s.s. The position of these relatively to the direction in which the dial will face must be carefully thought out before setting the position in the ground. In any case the help of a compa.s.s will be needed to decide which is the north.

Having set in the post and rammed the earth tightly round it, loosen the bracket supporting the vane rod so that the vane bevel clears the dial bevel. Turn the vane to true north, set the dial arrow also to north, and raise the bevel so that it meshes, and make the bracket tight.

Note.--In the vicinity of London true north is 15 degrees east of the magnetic north.

The pole must be long enough to raise the vane clear of any objects which might act as screens, and its length will therefore depend on its position.

As for the height of the dial above the ground, this must be left to individual preference or to circ.u.mstances. If conditions allow, it should be near enough to the ground to be examined easily with a lamp at night, as one of the chief advantages of the system is that the reading is independent of the visibility of the vane.

A Dial Indoors.--If some prominent part of the house, such as a chimney stack, be used to support the pole--which in such a case can be quite short--it is an easy matter to connect the vane with a dial indoors, provided that the rod can be run down an outside wall.

An Electrically Operated Dial.--Thanks to the electric current, it is possible to cause a wind vane, wherever it may be set, to work a dial situated anywhere indoors. A suggested method of effecting this is ill.u.s.trated in Figs. 158 to 161, which are sufficiently explicit to enable the reader to fill in details for himself.

[Ill.u.s.tration: FIG. 158.--Plan and elevation of electric contact on vane post.]

In-this case the vane is attached (Fig. 158) to a bra.s.s tube, closed at the upper end, and supported by a long spike stuck into the top of the pole. A little platform carries a bra.s.s ring, divided into as many insulated segments as the points which the vane is to be able to register. Thus, there will be eight segments if the half-points as well as the cardinal points are to be shown on the dial. The centre of each of these segments lies on a line running through the centre of the spike to the compa.s.s point to which the segment belongs. The tube moves with it a rotating contact piece, which rubs against the tops of the segments.

Below it is a "brush" of strip bra.s.s pressing against the tube. This brush is connected with a wire running to one terminal of a battery near the dial.

[Ill.u.s.tration: FIG. 159.--Magnetic recording dial.]

The Dial.--This may be either vertical or horizontal, provided that the arrow is well balanced. The arrow, which should be of some light non-magnetic material, such as cardboard or wood, carries on its lower side, near the point, a piece of soft iron. Under the path of this piece is a ring of equally s.p.a.ced magnets, their number equaling that of, the segments on the vane. Between arrow and magnets is the dial on which the points are marked (Fig. 159).

Each segment is connected by a separate wire with the corresponding dial magnet, and each of these, through a common wire and switch, with the other terminal of the battery (Fig. 161).

In order to ascertain the quarter of the wind, the switch is closed. The magnet which is energized will attract the needle to it, showing in what direction the vane is pointing. To prevent misreading, the dial may be covered by a flap the raising of which closes the battery circuit. A spring should be arranged to close the flap when the hand is removed, to prevent waste of current.

[Ill.u.s.tration: FIG. 160.--Another type of electric dial with compa.s.s needle for pointer.]

The exact.i.tude of the indication given by the arrow depends on the number of vane segments used. If these are only four, a N. read- ing will be given by any position of the vane between N.E. and N.W.; if eight, N. will mean anything between N.N.E. and N.N.W. Telephone cables, containing any desired number of insulated wires, each covered by a braiding of a distinctive colour, can be obtained at a cost only slightly exceeding that of an equal total amount of single insulated wire. The cable form is to be preferred, on account of its greater convenience in fixing.

The amount of battery power required depends on the length of the circuit and the delicacy of the dial. If an ordinary compa.s.s needle be used, as indicated in Fig. 160, very little current is needed. In this case the magnets, which can be made of a couple of dozen turns of fine insulated wire round a 1/8-in soft iron bar, should be arranged spokewise round the compa.s.s case, and care must be taken that all the cores are wound in the same direction, so as to have the same polarity. Otherwise some will attract the N. end of the needle and others repel it. The direction of the current flow through the circuit will decide the polarity of the magnets, so that, if one end of the needle be furnished with a little paper arrow-head, the "correspondence" between vane and dial is easily established. An advantage attaching to the use of a compa.s.s needle is that the magnet repels the wrong end of the needle.

[Ill.u.s.tration: FIG. 161.--General arrangement of electric wind recorder.]

The brush and segments must be protected from he weather by a cover, either attached to the segment platform or to the tube on which the vane is mounted.

The s.p.a.ces between the segments must be filled in flush with some non-conducting material, such as fibre, vulcanite, or sealing-wax; and be very slightly wider than the end of the contact arm, so that two segments may not be in circuit simultaneously. In certain positions of the vane no contact will be made, but, as the vane is motionless only when there is no wind or none to speak of, this is a small matter.

XXIX. A STRENGTH-TESTING MACHINE.

The penny-in-the-slot strength-testing machine is popular among men and boys, presumably because many of them like to show other people what their muscles are capable of, and the opportunity of proving it on a graduated dial is therefore tempting, especially if there be a possibility of recovering the penny by an unusually good performance.

For the expenditure of quite a small number of pence, one may construct a machine which will show fairly accurately what is the value of one's grip and the twisting, power of the arms; and, even if inaccurate, will serve for compet.i.tive purposes. The apparatus is very simple in principle, consisting of but five pieces of wood, an ordinary spring balance registering up to 40 lbs., and a couple of handles. The total cost is but a couple of shillings at the outside.

Fig. 162 is a plan of the machine as used for grip measuring. The base is a piece of deal 1 inch thick, 2 feet long, and 5-1/2 inches wide. The lever, L, is pivoted at P, attached to a spring balance at Q, and subjected to the pull of the hand at a point, R.

The pressure exerted at R is to that registered at Q as the distance PQ is to the distance PR. As the spring balance will not record beyond 40 lbs., the ratio of PQ to PR may conveniently be made 5 to 1, as this will allow for the performances of quite a strong man; but even if the ratio be lowered to 4 to 1, few readers will stretch the balance to its limit.

The balance should preferably be of the type shown in Fig. 162, having an indicator projecting at right angles to the scale through a slot, as this can be very easily fitted with a sliding index, I, in the form of a 1/4-inch strip of tin bent over at the ends to embrace the edges of the balance.

CONSTRUCTION.

[Ill.u.s.tration: FIG. 162.--Plan of strength tester.]

[Ill.u.s.tration: FIG. 163.--Grips of strength tester.]

As the pressures on the machine are high, the construction must be solid throughout. The lever frame, A, and pivot piece, C, should be of one-inch oak, and the two last be screwed very securely to the baseboard. The shape of A is shown in Fig. 163. The inside is cut out with a pad saw, a square notch being formed at the back for the lever to move in. The handles of an old rubber chest expander come in useful for the grips. One grip, D, is used entire for attachment to the lever; while of the other only the wooden part is required, to be mounted on a 1/4-inch steel bar running through the arms of A near the ends of the horns. If a handle of this kind is not available for D, one may subst.i.tute for it a piece of metal tubing of not less than 1/2-inch diameter, or a 3/4-inch wooden rod, attached to an eye on the lever by a wire pa.s.sing through its centre.

A handle, if used, is joined to the lever by means of a bra.s.s plate 3/4 inch wide and a couple of inches long. A hole is bored in the centre somewhat smaller than the k.n.o.b to which the rubber was fastened, and joined up to one long edge by a couple of saw cuts. Two holes for good-sized screws must also be drilled and countersunk, and a socket for the k.n.o.b must be scooped out of the lever. After making screw holes in the proper positions, pa.s.s the shank of the k.n.o.b through the slot in the plate, and screw the plate on the lever. This method holds the handle firmly while allowing it to move freely.

The lever tapers from 1-1/2 inches at the pivot to 5/8 inch at the balance end. The hole for the pivot--5/16-inch steel bar--should be long enough to admit a piece of tubing fitting the bar, to diminish friction, and an important point, be drilled near the handle edge of the lever, so as to leave plenty of wood to take the strain. The last remark also applies to the hole for the balance pin at Q.

The balance support, B, and the pivot piece, C, are 2-1/2 and 2-7/16 inches high respectively. Run a hole vertically through C and the baseboard for the pivot, which should be 4-1/2 inches long, so as to project 1 inch when driven right home. Take some trouble over getting the holes in L and C quite square to the baseboard, as any inaccuracy will make the lever twist as it moves. To prevent the pivot cutting into the wood, screw to the top of C a bra.s.s plate bored to fit the pivot accurately. The strain will then be shared by the screws.

The horns of A should be long enough to allow the outside of the fixed grip to be 2-1/4 inches from the inside of the handle.

The balance is secured first to the lever by a pin driven through the eye of the hook, and then to B by a 3-inch screw pa.s.sed through the ring. The balance should just not be in tension.

When the apparatus is so far complete, test it by means of a second balance applied to D. Set the scale-marker at zero, and pull on the D balance till, say, 35 lbs. is attained. If the fixed balance shows 7 lbs. on what is meant to be a 5 to 1 ratio, the setting of R relatively to P and Q is correct. If, however, there is a serious discrepancy, it would be worth while making tests with a very strong balance, and establishing a corrected gradation on a paper dial pasted to the face of E.

For twisting tests we need a special handle (see Fig. 164), which is slipped on to the pivot and transmits the twist to L through a pin pressing on the back of the lever. The stirrup is made out of strip iron, bent to shape and drilled near the ends for the grip spindle. To the bottom is screwed and soldered a bra.s.s or iron plate, into the underside of which the pin is driven.

[Ill.u.s.tration: FIG. 164.--Handle for twisting test.]

To prevent the handle bending over, solder round the pivot hole 3/4 inch of bra.s.s tubing, fitting the pivot closely.

Tests.--Grip tests should be made with each hand separately. The baseboard should lie flat on a table or other convenient support, and be steadied, but not pushed, by the hand not gripping.

Twisting tests may be made inwards with the right hand, and back-handedly with the left. The apparatus is stood on edge, square to the performer, resting on the horns of A and a support near the balance.

Finger tests are made by placing the thumb on the front face of B, and two fingers on the farther side of the lever, one to the left and the other to the right of the tail of the balance.

x.x.x. LUNG-TESTING APPARATUS.

The capacity of the lungs, and their powers of inspiration and expiration, can be tested by means of easily constructed apparatus which will interest most people who are introduced to it. The reduction of the capabilities of the lungs to figures affords a not unprofitable form of entertainment, as even among adults these figures will be found to vary widely.

Air Volume Measuring.--The air which the lungs deal with is scientifically cla.s.sified under four heads:

1. Tidal air, which pa.s.ses into and out of the lungs in natural breathing.

About 30 cubic inches in an adult (average).

2. Reserve air, which can be expelled after a normal expiration. About 100 cubic inches.