A reported forty thousand volts, from a bucket of water and gravity.
Part V is about things that were made, and it opens with a Victorian design now often rebuilt with two cans, two induction rings and dripping water. It can generate a spark you can hear without a mains supply. It is also one of the few experiments in this Codex a reader can reproduce with ordinary materials.
Who was Lord Kelvin?
William Thomson was born in Belfast in 1824 and became professor of natural philosophy at the University of Glasgow in 1846. He held that chair for 53 years. His work helped establish thermodynamics and an absolute temperature scale; his electrical instruments and counsel also helped make transatlantic telegraphy practical. He was a physicist who repeatedly turned theory into apparatus that could measure a subtle effect.
Water drops were part of that instrument-making. In 1860 he discussed a water-dropping collector for atmospheric electricity. In his 1867 paper he described the self-acting, two-stream apparatus that now bears his name: each collecting side induces charge in the opposite stream, so a small initial imbalance grows. Kelvin was demonstrating electrostatic induction and feedback; the falling water supplied the work.
When he described this machine, he was Sir William Thomson. The title Lord Kelvin came in 1892, from the River Kelvin near Glasgow. His published apparatus used Leyden jars and more elaborate receivers; the cans-and-rings version below is a teaching reconstruction.
The streaming potentials section examines charge separation at a solid–water boundary, while the waterfall explores electrification by spray. Kelvin's dropper is a different mechanism: an electric field induces charge as each drop breaks free. Reading them together reveals several ways moving water and electrical charge can interact.
Build it yourself
Callum Coats built a Kelvin dropper while writing Living Energies and reports an arc across two centimetres, which he estimated at around 40,000 volts. Air breakdown depends on humidity, pressure, electrode geometry and gap, so the responsible reading is tens of kilovolts—not an exact voltmeter measurement.
The Kelvin water dropper
Two falling streams, cross-wired rings and insulated collectors turn gravitational work into a growing electrical potential. The animation below is a schematic model.
A residual charge or nearby electric field seeds a tiny imbalance. Suppose the left ring is slightly negative; the machine amplifies that starting difference.
While the water is still connected to the reservoir, the negative ring redistributes charge near the forming drop. When it breaks free inside the ring, it carries a positive charge. The ring never touches the water.
The left can accumulates positive charge, drop by drop. The right can, by the mirror process, accumulates negative.
Here is the trick: each can is wired to the opposite ring. The positive left can feeds the right ring — making it more positive — which makes the right drops more negative — which makes the right can more negative — which feeds the left ring…
The imbalance amplifies itself through positive feedback until the air between the electrodes breaks down. Breakdown depends on humidity, pressure, gap and electrode shape; a two-centimetre arc indicates tens of kilovolts, and Coats reports roughly 40,000 V.
What it takes
A raised reservoir with two outlets adjusted to drip, not stream — separated drops are essential, since a continuous jet shorts the charge back up to the tank. Two metal rings (cut tin, foil-wrapped card, copper tube) mounted a few centimetres below the nozzles. Two metal cans standing on good insulators — glass, dry wood, plastic. And wire, crossed.
Drops must break free inside the ring
The induction happens at the instant a drop separates while still within the ring's field. If the drops pinch off too high or too low, the charge never commits and nothing accumulates. Adjusting nozzle height and drip rate is most of the fiddling — and getting it right is the difference between a dead rig and a spark.
Dry air, and patience
Humidity is the enemy: damp air conducts, bleeding charge away as fast as it builds. It works best in winter or a dry room, and it needs tens of seconds of steady dripping before the exponential runaway becomes visible. Nothing happens, nothing happens — then it fires, and keeps firing on a rhythm set by the drip rate.
A gravity-to-voltage converter
Not a source of new energy. Each charged drop falls toward a like-charged can that repels it, transferring a little of its gravitational energy into separated charge. The voltage can be large while the available current and power remain small; their exact values depend on the flow, insulation and geometry.
Kelvin droppers are reproducible electrostatic generators, and discharges can indicate tens of kilovolts at extremely small current. Electrostatic induction and the positive-feedback loop created by the cross-wiring are standard electrostatics. The apparatus converts part of the water’s gravitational potential into electrical potential; it does not create energy.
That falling water performs electrical work you can see, that cross-wiring creates positive feedback, and that material, humidity and geometry determine how much charge accumulates. Experiments confirm charged droplets and, in microfluidic versions, electrohydrodynamic breakup. The small orbital paths in this animation are illustrative rather than a measured feature of every standard apparatus.
The spark does not imply an excess-energy source. The apparatus draws on the water's height; charging stops when leakage, droplet deflection or a discharge overtakes the feedback. Every joule was already in the water’s height. A high voltage alone says little about usable power, and no particular current or spark voltage is guaranteed for every build.
Because it sets the terms for everything that follows. The dropper proves that falling water really does perform electrical work you can watch happen — and, in the same breath, that the quantity is minute. That is exactly the discipline the rest of Part V requires: every device from here on is a concentrator of energy that already exists, never a source of new energy. Hold that distinction and the spiral pipe, the clay egg, the ram and the Lily all make sense. Drop it, and you get the implosion machines. Nature’s water-spray route to charge separation is the waterfall, which works by a different mechanism from this dropper.