Zoetrope

Cut a strip of heavy card 950 x 200 mm. Rolled into a cylinder that gives a drum about 300 mm across — big enough for drawings you can actually see.

Mark 12 divisions of 79 mm along the strip. Twelve is a good working number — enough frames for smooth motion, few enough to draw in an afternoon.

Cut a slit 3 mm wide and 50 mm tall at each of the 12 marks, in the upper half of the strip. Narrow slits give a sharper image and a darker one; wide slits are bright and smeared.

Roll the strip into a cylinder with the slits at the top and join the overlap. Keep it round — an oval drum changes the viewing distance as it spins and the image breathes in and out.

Cut a disc to match the drum diameter and glue the cylinder onto its rim. The base carries the drum and the bearing.

Fit a dowel through the centre of the base into a block, or drop the base onto a lazy-Susan bearing. It must spin freely for several seconds after one push — friction is what limits your usable speed range.

Spin it and watch for wobble; shim the base until it runs true. A wobbling drum shifts the slits vertically and the image jumps.

Cut a paper strip to sit inside the drum below the slits and divide it into the same 12 spaces. Draw one phase of a cycle in each — a bouncing ball is the easiest first sequence.

Make frame 12 lead back into frame 1. The drum has no beginning, so any sequence that does not close shows a visible jolt once per revolution.

Drop the strip inside against the wall, spin the drum and look through the slits at the far side. Look through, never over — the whole effect depends on the slit acting as a shutter.

Time ten revolutions with a stopwatch and divide. Twelve slits per turn means images per second is twelve times revolutions per second — find the speed at which the motion looks smooth and write the number down.

Let it slow until the motion breaks into separate flashes and note that rate too. Between those two numbers is the working range of every projected moving image ever made.

Now load a strip with 11 or 13 drawings into the 12-slit drum. The figure creeps slowly round the drum instead of staying put, because each glimpse arrives slightly out of register with the last. That is stroboscopic drift — the same effect as backward-turning wheels in film.

Make a second drum with 6 mm slits and compare. Wider slits let in more light and more movement during the exposure, so the picture is brighter and blurrier. Every shutter since has traded the same two things against each other.

Horner, 1833. The Bristol mathematician William George Horner devised the slitted drum and called it the Daedalum. His version put the viewing slits between the pictures rather than on a band above them, which meant the images could not simply be swapped for a new strip. It sold almost not at all.

The name and the success came thirty years later. Peter Desvignes patented and demonstrated a version in Britain in 1860. In the United States William Ensign Lincoln — a Brown University undergraduate, about eighteen years old — devised the definitive form with the slits on a band above the pictures, so strips became interchangeable. He assigned it to the toy makers Milton Bradley and was granted his patent in April 1867. It became a mass-market toy on both sides of the Atlantic almost immediately. The invention that mattered commercially was not the drum, it was the replaceable strip.

The Chinese claim, honestly stated. The inventor Ding Huan is recorded in second-century China as having made a device in which painted vanes turned on rising heat from a lamp. It is often presented as the first zoetrope. It is not clear from the sources whether it produced any illusion of animation at all, or simply spun physical figures around — and the honest position is that we do not know. Rotating lamp-driven figures are a real Chinese tradition; a working animation device in 180 AD is a much larger claim than the evidence supports.

Where it leads. The zoetrope is the phenakistoscope's descendant and the praxinoscope's ancestor — Émile Reynaud replaced the slits with a ring of mirrors in 1877, recovering the light the slits threw away. The line runs directly to the film projector, which is a zoetrope with a lamp behind the strip and a shutter in place of the slit.