The sun arbor
Cut the sun arbor from bell brass, not clock brass. The warmer alloy throws a softer glint under candlelight and forgives the lecture hall's dust. Polish only the shoulder. Leave the base with tooth marks so oil has somewhere to sleep.
Alabaster & Vane, Clerkenwell - Est. 1774
The Brass Orrery
A hand-cranked mechanical planetarium for observatories, naval tutors, and private collectors who prefer their heavens oiled, geared, and accountable.
Current plateNo. 30 of 50
Trial meridianGreenwich, 51.48 N
Main wheel231 teeth
Heliocentric rig engaged. The sun holds the center arbor.
Meridian date
20 March 1774
Hidden worm gear: six turns to a decade, one drop of oil after each lecture.
Instrument house record
The shop that taught brass to remember the sky.
Thomas Alabaster opened the first room above a watchmaker's stable in 1774 with three lathes, two apprentices, and a commission from the Royal Mathematical School for a demonstration machine that could survive the hands of twelve-year-old midshipmen. His partner, Mara Vane, supplied the solution: make the mechanism beautiful enough that no boy dared force it.
The surviving ledgers list 186 complete orreries, 41 repairs after sea travel, and seven "philosophical re-riggings" for patrons who insisted on seeing the heavens from Earth. Every piece in the current catalogue follows Vane's rule of sympathy: a planet arm may simplify distance, but never period. Mercury must hurry. Saturn must make the room wait.
186complete machines
41sea-travel repairs
7philosophical re-riggings
231master crown teeth
Ephemeris table
The machine's reason, written in numbers.
The longitudes below are computed from the same relative periods that drive the arms above. The workshop scale is compressed for the eye, but the timing ratios are left intact.
| Body | Sidereal period | Gear train | Current longitude |
|---|---|---|---|
| Mercury | 87.969 days | 19:47:231 | 12 deg Aries |
| Venus | 224.701 days | 31:61:231 | 28 deg Taurus |
| Earth | 365.256 days | 53:84:231 | 0 deg Libra |
| Mars | 686.980 days | 71:112:231 | 17 deg Scorpio |
| Jupiter | 4,332.590 days | 97:181:231 | 4 deg Capricorn |
| Saturn | 10,759.220 days | 127:199:231 | 21 deg Aquarius |
Craftsman's notes
Gear-cutting instructions from the Vane folio.
The 231-tooth crown
The master crown carries every planetary compromise. Vane used 231 teeth because it receives Mercury's quick wheel without chattering and lets Saturn's worm advance with almost judicial slowness: one visible nudge in eleven turns.
Garnet epoch pin
A red stone marks the vernal setting of 20 March 1774. Apprentices were told it was decorative. The senior ledger says otherwise: if the pin is removed, the table will still turn, but nobody in the room agrees what year it is.
Geocentric conversion
Do not reverse the planets. Re-hang the frame of reference. The earth arbor becomes the witness, the sun receives a traveling yoke, and all outer arms are carried by their differences. The visitor should see the argument happen.
Selected commissions
Three machines still known by the sound of their crank.
The Blackfriars Lecture Orrery
Built for Amelia Rook's public astronomy rooms. A ratchet stop at every month let paying visitors hear "April" click into place.
The Winterless Academy Cabinet
A mahogany traveling case with frost-bitten ivory dials, ordered for a school in Tromso where the first lesson was patience.
The Penzance Tide and Planet Engine
A hybrid tide predictor and orrery with lunar gearing removed after it made the harbor master distrust his own tables.
Observatory nocturne
Program notes for the midnight demonstration.
At 23:40 the brass hood is lowered and the room lamps are extinguished to half-wick. Visitors stand on the green line, never the red. The demonstrator advances the crank one decade at a time, pausing at 1846 so Neptune can be mentioned without being represented. The omission is deliberate: this is a six-planet teaching instrument, not a census.
At the geocentric changeover the machine is allowed to sound untidy. Elbows cross. The sun travels. Mars performs its retrograde joke. Vane's notebooks call this "the useful embarrassment," because the mechanism does not mock the old model; it shows why human eyes could believe it.
- Half-wick lamps; garnet epoch pin aligned.
- Ten decades cranked; Saturn audibly refuses haste.
- Geocentric re-rig; Mars begins the useful embarrassment.