Chapter VII: Moving Models, and How to Make Them; Or, ‘drop a Penny in

THE BOX AND THE MODEL WILL WORK.’

BY FRANK CHASEMORE.

Many a penny have I invested when, as a lad, visiting such places of amusement as the Crystal Palace, Polytechnic, London Crystal Palace, and Pantechnicon, in obedience to the entreaty forming the sub-title of this chapter, placed on the cases containing models and figures; and I yet very vividly remember the delight experienced from seeing the models start into motion. Indeed, even now, though arrived at man’s estate, I rarely miss dropping a penny into the coffer of any case containing a moving model when I chance to come across one.

Now these models, complicated as they may sometimes seem, can be easily made by any boy who can use his tools, and, as the construction and exhibition of them will afford great amusement, I propose in this chapter to give detailed practical instructions for making them.

The subjects I have chosen are a windmill, a yacht in full sail, a watermill with real water, dancing niggers, etc., so that there should be sufficient variety to suit all tastes and skill.

A MODEL WINDMILL.

The windmill being the simplest in construction of the working models, we will take it first. The model, with the necessary pictorial background, is to be enclosed in a case, which will bear somewhere on the front of it the legend forming the title of this chapter, and the sails will go merrily round on dropping a penny into the box, thus practically illustrating the old song, ‘Money makes the mill to go.’ The cost of the whole model and case will be something under 8_s._ Now for the construction.

We will make the case first. For this get some half-inch deal board, 12 in. wide, and plane it smooth on both sides. Cut the pieces for the back, top, bottom, and sides, and square them up true. The dimensions of these pieces are as follows: the back, 20 in. long and 12 in. wide; the top and bottom pieces, 12 in. long and 10 in. wide; and the two side pieces are each 20 in. long and 10 in. wide.

Having cut and trued up these pieces, proceed to form them into a box by joining the edges by dovetailing, if you are skilful at cabinet-making, or get some friendly carpenter to do it for you, if you are not up to the work. If you cannot manage either to do it yourself or to get it done for you, the parts can be joined with glue and screws, but the side pieces will have to be cut one inch shorter than for dovetailing, in order that the top and bottom pieces may fit in flush with the back piece.

The front of the box is to be closed by a door, of which the upper 12 in. is of glass. Make the door out of a piece of half-inch board, 8 in. by 11 in. for the bottom piece, and fasten to each end a strip of wood 20 in. long and 1/2 in. square, so that one end of each strip is flush with the lower edge of the board, leaving 12 in of each strip projecting beyond the upper edge.

These strips should have a groove 1/8 in. deep cut in them to hold the glass. This you had better get cut for you. Put your glass, which must be about 11-1/4 in. wide and 11 in. long, into the grooves, and the upper edge of it will be half an inch from the ends of the strips. Fasten it in by a cross-piece of wood 1/2 in. square and 11 in. long, glued and screwed to the two side strips.

If you prefer it, the glass can be put in the door after the manner of window-panes. In this case the side and top strips must have a rebate cut in them, and the top edge of the wooden portion served in the same way. You must choose for yourself which method you will adopt. Either will do, but the latter is perhaps the neater.

In the top of the right-hand end of the wooden portion cut a slot large enough to allow the necessary penny to pass freely. The door you will fasten to the box with two small brass hinges, and you must put a small brass hook on the other side of the box to keep it fastened. But it will be better if you do not hang the door till the inside arrangements are completed, for fear of breaking the glass.

Fig. 1 represents the case and model complete. Divide the interior of the box into two portions by a horizontal partition, fastened to the back and sides by glue and screws. The space below the partition is to be 7 in. deep. In the right of this space fit a cash drawer 9 in. long, 3 in. deep, and 3 in. wide, to hold the pennies. The side of this drawer nearest the machinery must have a slot cut in it for the starting lever (A, Fig. 3) to work in. The sides of the case are made of wood, so that the working of the model can only be seen from the front and so that the flow of pennies will be larger.

Paint the back of the inside of the case to represent a landscape, or a suitably coloured picture can be pasted in, and serve the horizontal partition in the same manner to represent ground, blending the back and ground together in a natural manner. Paint also the top board to represent sky.

Make the mill out of wood or cardboard. It is to be 7-3/4 in. high, and the holes for the spindle carrying the sails 5-3/4 in. from the bottom. The sails are to be 9-1/2 in. across, and can be made of wood or cardboard, or, better still, wood cross-pieces with cardboard sails. Make the spindle of iron wire 1/8 in. in thickness. It should be about 3-1/2 in. long. Flatten one end of the wire and drive it into the centre point of the cross-pieces of the sails, being careful to keep it quite square and upright.

Pass the spindle through the holes in the back and front of the mill, and put a knob of sealing-wax on the end, to prevent it working out when the mill is at work. If the mill is made of cardboard, the inside must be strengthened with wood to support the spindle.

We will next turn our attention to the mechanism to set the mill in motion. Very few of my readers possess the tools and skill to use them necessary to cut and fit the wheels, and, as it would come very expensive to get them made specially, it will come very much cheaper to buy one of the cheap eight-day clocks, which will suit our purpose admirably. These can be procured at most of the suitable shops, and will cost about 5_s._ 6_d._

Take the frame and works out of the clock case, and remove the pendulum and hands, as you will not require them. If you now turn round the spindle on which the minute hand fits, you will notice that, although the parts that carry the hands are in motion, the rest of the wheels are stationary. On examining these hand-turning wheels carefully, you will notice that the one carrying the minute hand is fixed on the central spindle by jambing only, and that it turns a small flat wheel which, in turn, gives motion to the wheel carrying the hour hand. This wheel is fixed to a tubular spindle, which fits over the spindle of the minute-hand wheel, which itself is tubular and jambs on the central spindle. Now, as you will not require this movement, take off the hour-hand wheel, and after removing the small flat wheel, replace it and fasten it, together with the minute-hand wheel, to the central spindle with solder.

Some of the cheap clocks have the minute hand fixed direct to the central spindle, the hour wheel only being tubular. In this case the hour wheel and the spindle must be soldered together after the small flat wheel has been removed. As you will not require the escapement wheel, push on one side the small spring clip that presses on the end of the spindle, and it will drop out.

You will now want a pulley wheel (B, Fig. 3). One of the wooden sheaves used in Venetian blinds for the cords to run over will do very well indeed, or if you possess a lathe you can turn one for yourself. It should be 1-1/2 in. in diameter and 1/4 in. thick, having a small hole right through the centre, of a size to fit tightly on the hour spindle of your works. Fig. 2 represents the frame after the wheels not required have been removed. Fig. 3 represents the starting lever and pulley. This pulley must have a notch 1/4 in. deep cut in one rim, for the hook of the lever to fall into and stop the machinery. This pulley must not be more than 1-1/2 in. in diameter, or you will not be able to get at the winding-up pin.

The frame carrying the wheels must now be mounted in its place under the horizontal partition. For this purpose fasten with screws a block of wood to the floor board, or back of the case, in such a position that the front of the frame is about 5-1/2 in. from the front of the case, and so that the centre of the wooden wheel is about 4 in. from the horizontal partition, and immediately under the spindle carrying the sails of the mill. The horizontal partition must have a slot cut in it, inside the mill, for the connecting cord to pass. The frame is to be fastened to the supporting block by screws, but before doing this you must make the all-important starting and stopping lever.

Get a piece of iron wire 1/8 in. thick, and about 10 in. long. Flatten one end and bend down about half an inch of this end to form a hook, standing about at right angles to the length; place this hook in the notch of the wheel when it is a little beyond the centre of the pulley, as seen in the cut, and cut the wire to such a length that the other end of it will be about 1 in. from the side of the case, when the gear is in position. Drill a hole crosswise through the wire about 3 in. from the hook, and fasten a small wire to the gear-frame, standing at right angles to it, about 2-1/2 in., measured horizontally from the spindle of the pulley, and near the top. This is for the lever to turn on, as shown in the cut. At the free end of the lever solder a piece of tin bent up on three sides like a small tray, with the edge not bent at the extreme end. This tray or scoop should be about 1-1/2 in. square, and is to catch the penny as it is dropped in.

The hooked end of the lever must be weighted, to slightly outbalance the other part, so that the hook will drop into the notch in the pulley. The frame can now be put in its place and fixed to the block with screws. Bend the long end of the lever till the scoop is 3-1/2 in. from the under side of the partition. In bending the lever you must also see that the scoop is horizontal, or the penny will not remain in it long enough to start the gear. Now connect the spindle of the sails and the wooden pulley-wheel by passing a silk cord or fine string round both tightly, and knotting the ends together.

Now on winding up the spring and pressing down the lever the works will start into motion and the sails will revolve. The speed can be regulated by placing the sails at such an angle that they will offer more or less resistance to the air.

The slot in the door for the insertion of the penny must be cut three-quarters of an inch below the upper edge of the wooden partition, and inside you must fasten a tin trough to conduct the penny to the scoop at the end of the lever. This trough must slope downwards to the edge of the scoop, or the penny will not fall into it, but remain just inside the hole.

The model is now complete, and works as follows: The spring having been wound up and the door closed, the works are kept from moving by the hook of the lever catching in the notch of the pulley, but on a penny being put into the hole, and sliding into the scoop at the other end of the lever, its weight presses down the scoop end and lifts the hooked end out of the notch in the pulley, which turns round, and continues to do so, carrying the sails of the mill round with it till the notch again comes under the hook, which (the penny having fallen out of the scoop into the drawer) falls into it and stops the machinery, giving one revolution of the pulley for a penny. The pulley being twelve times larger than the spindle of the sails, these will revolve twelve times each time the model is started. The model will work about 204 times each time it is wound up.

A MODEL CUTTER YACHT.

Having finished the windmill to your satisfaction, we will now turn our attention to the construction of a model requiring rather more complex machinery. This is shown at Fig. 4, and represents a cutter-yacht sailing on the port tack, on a lee shore; which, if carefully made, so as to produce the effect of the rolling and pitching of a real yacht upon a real sea, will catch many a penny.

The case is made exactly in the same manner as the former one, and has the same dimensions, but has no horizontal partition, only a cross-piece in the front, half an inch square.

The inside of the back you must paint to represent a cliff and sky, or you can paste a coloured picture of the same on it.

The yacht is to be 5 in. long, and is to be set in a sea of silk, which will be described further on. If you prefer it, a full-rigged ship can be substituted for the yacht. For the machinery you will require, as before, an eight-day clock movement, some brass wire, and three or four pulley-wheels. Fig. 5 shows the front view of the mechanism when complete, and Fig. 6 the end view of the same.

As was the case in preparing the works for the windmill, you will require to make some alteration in the wheels, but in this case, as the hour and minute movement will be required for the starting gear, the minute spindle only is to be soldered to the central spindle, and the small flat wheel retained in its place. The escapement wheel must also be retained. B (Fig. 5) is one of the wooden pulleys, 1 in. in diameter, fixed to the minute-hand spindle, and is in connection with another pulley-wheel of the same size (B), turning on a screw fixed in a block of wood fastened to the floor-board in such a position that the centres of the two pulleys are the same height from the floor and 4-1/2 in. apart. O is a lever of wire about 7 in. long, working on a pivot passing through it about 2-1/2 in. from the end C. This end is connected with the keel of the boat, and the other end is weighted, to balance the boat.

Now take your boat, and at each end of the keel fix a small brass plate having a hole drilled in it (FF, Fig. 5), 4-1/2 in. apart, and fix another plate drilled in the same way at C, about 2-3/4 in. from the stem of the boat. Take two pieces of wire 5 in. long and bend one end of each into an eye and the other end into a hook, crosswise with regard to the eye, and hook a wire into each of the plates FF, on the keel of the boat, and connect the other ends with the pulleys B and B by two small brass screws passing into the fronts of BB, as shown in Fig. 5, and arrange the pulleys so that one of the pivots shall be up while the other is down.

All these joints and connections must work freely, although not loosely. The two pulleys, BB, you must connect with a cord passing round both. The pitch of the vessel is regulated by the distance the pivot screws are from the centres of the pulleys, which should be about half an inch. You must next make the regulating gear or fly E (Fig. 5). To do this you must take out the pin from the left-hand lower corner of the frame-plate and prise up the plate and take out the fourth wheel near R (Fig. 5), and on the spindle of it fix a pulley, which can be readily done in the following manner. Cut a small notch in one side of the hole in the centre of the pulley just large enough to admit a piece of your wire. Solder about half an inch of this wire along one side of the spindle about the middle of it, and force the pulley on to the spindle over this piece, and it will jamb lightly and be keyed to it. Fig. 7 will show you how to cut the hole in the pulley.

Now return the wheel to its place and re-fasten the frame-plate. Next you must make the fly E. Get a small brass pulley about 1/4 in. in diameter, and to it solder a strip of tin cut to the shape shown, but being wider in proportion at the ends, say 1 in. wide and 4 in. long. Twist the ends of this fly askew like the fans of a screw propeller, so that it will catch the wind in revolving. Now fix a block of wood to the bottom of the case and fix the fly to it by a small brass screw passing through its centre, so that it works freely and is 3-1/2 in. from the centre of the driving pulley R and level with it. Fasten a block of wood to the back of the case, in which you must fix the screw N (Fig. 5) for the lever O to pivot on. You must next make the starting gear. This is shown in Fig. 8.

As we require the pulleys BB to revolve about twelve times, and as they are attached to the minute-hand spindle, the hour-hand spindle will revolve once. Therefore, on this spindle fix behind the pulley B, by soldering, a circular plate of tin or brass, a little larger than the pulley, and cut in one edge of it a slot a quarter-inch deep and one-eighth of an inch wide. Make your lever as before, but long enough for the hook to catch in the teeth of the wheel C, Fig. 8; and solder a piece of tin to the lever, to fall at the same time into the slot in the disc A, Fig. 8. This piece of tin must be long enough to keep the hook free of the teeth of the wheel C during the revolution of the disc A. The length of the other part of the lever is to be the same as for the windmill. Fig. 6 shows an end view of the machinery. K is a wire connecting the keel with the lever Q, and helps to give the rolling motion so suggestive to voyagers.

Fix your gear into the case in such a position that the keel of the boat will be 7 in. above the floor of the box, and bend the starting lever so that the scoop will be the same distance from the floor and front of the box as in the former case. You have now to make the sea. Get a piece of silk of the kind called Persian, dark green or ‘undecided’ blue, about 18 in. square, and in the middle of it cut a slit 6 in. long, and in this slit fasten the hull of the boat with glue, puckering up the silk, to form the waves on the sides of the vessel. Crumple the whole of the silk into miniature waves, and glue the edges round the edges of the case and to the strip of wood fastened across the front 7 in. from the floor. Touch the crests of the waves with white paint. The silk waves will rise and fall with the motion of the vessel, and appear themselves to be the cause of that motion. If the silk has a tendency to drop in, it can be supported by a floor-board, 7 in. from the bottom, with a hole cut in the centre 5 in. long and 2 in. wide for the boat to work in, and a slot cut for the wire K, Fig. 6. Be very careful that all the joints and connections work easily, or a jerky motion will be the result.

Wind up the works and drop in a penny, and the lever hook will be lifted out of the escapement wheel, and round will go the pulleys, causing the little ship to pitch and roll till the slot A comes round again, when down falls the lever hook and stops the movement. The pace of the movement can be regulated by the angle of the fans of the fly catching more or less air.

As the minute spindle revolves twelve times, the pulleys will revolve only once, which will give about seventeen revolutions each time of winding.

DANCING ‘NIGGERS.’

Fig. 9 is a view of a case of dancing ‘niggers,’ and is easily made. In the sketch the figures are one-third the real size.

The case measures 9 in. high, 7 in. wide, and 7 in. deep. The back forms a hinged door by which you can get at the gear. The slit for the penny is in the top, and near the right-hand back corner. The legs of the right-hand figure are both made separate from the body and jointed at the knees. They are fastened to the body by small pins, to allow of free working. This figure you must strengthen by glueing a piece of wood behind it 1 in. long, 1/2 in. wide, and 1/4 in. thick. The other figure has only the left leg moveable, and must not be jointed at the knee. Glue a strip of wood about 1/2 in. wide and 1/4 in. thick right up the back of this figure, and glue it to the floor board. The left leg must have a similar piece of wood glued behind it, and projecting 1/2 in. longer at the thigh end. Fix the leg to the body by a small pin, for it to work freely on, and in the piece of wood projecting fix, at right angles, a piece of wire about 2 in. long, and cut a curved slit in the background for this to work in, when the figure is about 1 in. from it.

This background you must make out of cardboard, and fix about 3 in. from the front of the case, which is glass. The background you can paint to any design you please, such as a street scene, or on the sands, and the floor to correspond.

Behind the right-hand figure cut a vertical slit in the background about 1/8 in. wide and 2 in. long, so that the centre of it comes opposite the centre of the figure when the feet are just touching the floor. Fix a piece of wire about 7 in. long into the centre of the figure behind, and at right angles to it, and bend this wire downwards at right angles about 2 in. from the figure. About 1 in. behind the background fix an upright block of wood, to come as high as the centre of the figure, and in front of it fix two small staples, one near the top, and the other about 2 in. lower, but directly under it. Into these slip the end of the wire attached to the figure, after passing it through the slot in the background. This will keep the figure in its place and allow of its moving up and down.

Prepare the works as for the yacht model, and also insert a pulley (A), as shown in Figs. 10 and 5. This is connected with another pulley (B, Fig. 10), which is fixed to a block by a screw that is countersunk below the face of it, and to which is fastened by a small screw two wires working freely and passing one to the wire from the left-hand figure, and the other to the cross-piece of the wire from the right-hand one, and connected with them by the ends being bent into rings. From the cross wire to the figure to the right is also hung a drop wire with a small weight at the end, to help to pull it down. Fig. 11 will explain the fixing of this gear. A fly must be also fitted to the movement, to check the pace. This can be fixed to the pulley (B) or in front of the escapement wheel. The stopping motion is the same as in Fig. 8, but more slots may be cut in the disc, to regulate the length of time allowed for a penny.

The works you must fix behind the background so that the starting lever comes conveniently for the penny in its fall.

With these three examples of the necessary clockwork you will be able by the exercise of a little ingenuity and the power of contriving to make moving models of any subjects that may suggest themselves to you, such as the following: a steamboat with revolving paddle-wheels, cobbler mending shoes, soldiers marching, etc., etc.

A REAL WATER-WHEEL.

I will now tell you how to make the model shown in Fig. 12, consisting of a water-mill working with real water, a small fountain in the middle, and children playing at see-saw in the background.

This model is worked with water-power only, and has no clockwork. The case you must make larger than in either of the former cases--24 in. high, 14 in. wide, and 14 in. deep; the height of the floor of the model from the bottom of the case 4 in., and the depth of the upper partition 4 in., the intermediate space closed by a glass door 16 in. by 14 in. The case must be made out of 1/2 in. stuff and well dovetailed together. In the right-hand bottom corner a drawer for the pennies with a slot in front. The back or one of the sides should have a door in it, to get at the machinery, should it at any time require attending to.

You must now make two zinc tanks, the top one air-tight, to occupy the whole of the upper space, the other also air-tight at first, to occupy the space left in the lower partition by the drawer. The top tank will be 13 in. by 13 in. by 3-1/2 in., and will have a small receiver, about 6 in. square by 1 in. deep, soldered to the bottom of it, and communication with it by a small hole, as shown in E, Fig. 13, about a quarter of an inch in diameter, and having also a small pipe passing from it to the outer air through the large tank. This pipe is not shown in the figure, but it is soldered to the top and bottom of the tank and the ends filed off flush. The zinc for the bottom and sides of the tanks can be cut out of one piece, as shown in Fig. 14. The edges of the tops should be turned over, to add strength. The soldering must be made air-tight. The background of the picture is a false back inserted about 2 in. from the true one, behind which the pipes are placed connecting the vessels together, as shown in Fig. 13, which is a back view.

These pipes must be carefully soldered in. A is the air-pipe to supply reservoir F when in use; B is the pumping-pipe, in the middle of which is fixed an india-rubber force-ball, to be procured at any india-rubber shop, in which is a small pin-valve, to prevent the water flowing back. This pipe extends from the bottom of tank G to the top of tank F, leaving a space of about 1/8 in. between the ends of the pipes and the metal of the tanks. C is a small pipe by which the water from the basin of the fountain is run into G. E is the receiver into which water from F runs, and from which two pipes lead, one to the wheel of the mill, and the other to the fountain. K is a regulating tap, to govern the supply of air and regulate the amount of water passed into E. D is the stopcock connected with the starting lever, which is about 6 in. long and soldered to the handle of the tap. This tap must work easily, and yet be air-tight.

The lever must be counterweighted, to close the tap when the penny has fallen off the scoop at the end of the lever. H is a small pipe fixed in the top of the tank G to allow the air to pass out when the water is running into it through C. The basin of the fountain should be made of zinc, and fastened to the tube C, and the jet is formed of the end of a blow-pipe connected to the tube from E. The rockery you must form of cinders and paint them to a suitable colour. The mill-wheel should be made of zinc and painted, and the water from it conducted to the basin of the fountain. The other pipe from E you must conduct to a position suitable to set the wheel in motion.

The see-saw you must place so that it can be set in motion by the axle of the mill-wheel, which is carried out long enough under the rockery-bank to reach it, and has a cross-piece of wire soldered to it at a point immediately under one of the figures, and which in revolving tips up one end of the board.

This end of the board is made, slightly heavier than the other, which will make it return to be again tipped up. We will now see how the model is worked. Pour water into the basin of the fountain till it is full, and open the starting lever as shown in Fig. 15. The bottom vessel will now be quite full. Now work the force-ball, which will pump the water out of G into F, the air rushing into G through the pipe H. As soon as the upper tank is full the starting lever is to be closed, and the model is ready to begin work. Now as F, Fig. 13, is an air-tight vessel, no water can run from F into E. But as soon as a coin is dropped into the scoop at the end of the lever A, Fig. 15, its weight presses it down and opens the cock D, which allows the air to be drawn into F, and consequently allows water to pass into E, Fig. 13.

The quantity of air allowed to pass is regulated by the extent to which K, Fig. 13, is opened. The water being in E, and this vessel communicating with the atmosphere through the pipe not shown in the Figs., the water falls into the two pipes, and is conducted by one to set the wheel in motion, and by the other to the fountain-jet, through which it issues and again falls into the basin, and thence again into G.

HOW TO MAKE A CHEAP CLOCK.

An ingenious and inexpensive timekeeper may be made by any boy for a few pence and a little labour. Buy a sheet of millboard, the thicker the better--size, 27 in. by 22 in.--cut off a strip 10 in. by 27 in., and shape it as shown in Fig. 16, the top part to be 10 in. square, and the lower 17 in. by 4 in. Next mark off the remainder of the millboard into three equal parts of 4 in. each, as shown in Fig. 17, then, with a straightedge and a sharp knife, cut half through the lines AA. This will form the two sides and back of the case. The funnel (B, Fig. 18) should be made of tin, with a square top to fit over the millboard, and have a very small aperture at the point; any tinman will make this for 3_d._ or 4_d._ The spindle (C, Fig. 18) must be 3-3/4 in. long, 3-1/2 in. deep in front, diminishing to 2 in. at back, have a screw-shaped groove from end to end, and work on a small spindle or axle, projecting 1 in. in front, for the hand to be connected to, and 1/2 an inch at rear. If the young horologist has not a lathe at his disposal, the spindle can be obtained from a turner for a few pence. The weight may be made of a piece of shaped stone, or of an empty stone ink-bottle, from the neck of which the cord passes over the bar (C), round the grooves of the spindle, and out of the hole (K). A small weight, such as a bullet, must be fastened to the other end. A piece of canvas should be glued round the edges of the case, and the whole painted with a good coating of Brunswick black, over which any design may be made, either with gold lines, grotesque figures, or coloured pictures. The dial should be of white paper, 7 in. in diameter, and the hand cut out of the spare millboard and then gilded. Four small reels (E, Fig. 17), such as are used for silk, should be glued on the back, to keep the case from the wall, and a ring fastened to the top to hang it by.

It is now ready for the motive power, which is obtained by the falling of sand, as in the hour-glass. The sand must be first well washed, dried, and sifted, to remove all stones, then poured through the case top to within two inches of the cross-bar (C, Fig. 18), the weight resting on the surface. As the sand runs through the funnel-point the weight will descend with it at the rate of about 1 in. per hour. The flow of sand will be perfectly equable from the time the case is filled until it is nearly empty, which is explained by the fact that the sand lies in a succession of conical heaps, only the _first_ of which presses on the bottom, the others throwing their weight on the sides of the case. A gallon of sand will be more than sufficient to fill the cases, and as it falls it should be caught in a vase placed beneath for that purpose. In winding up the clock the inside weight must be raised to the cross-bar by pulling down the bullet end of the cord, and the sand poured through a paper funnel into the top of the case, care being taken to set the hand to the right hour. A clock of the dimensions here given will work for about twelve hours, but by lengthening the sand-box the working hours will be increased in proportion. It will save time and trouble to have a double supply of sand and two vases, and use them alternately. Of course one does not pretend that such a simple clock as this will keep accurate time.