Manifesto
We believe a smoke ring
can make the world better
A ring of air costs nothing, belongs to no one, and asks nothing of the people who see it. It rises, it travels, it comes apart. In the few seconds it holds together, everyone in the field is looking at the same thing.
People love to see them. We have watched arguments stop mid-sentence. We have watched strangers point at the sky together. Whatever a person was carrying, they set it down for as long as the ring lasts — and some of them do not pick it all back up.
So we build the drums, and we go out at dusk, and we send sculpture into still air. Not to be kept. Only to be seen.
Nothing that beautiful should be permanent, and nothing that temporary should be withheld.
Testimony
Accounts from the field
“I had not spoken to my brother in nine years. A ring came over the fence, wobbled, and fell apart above the driveway, and we both laughed at the same time. I called him that night.”
“I came to that lot angry the way I had been angry for a long time. The ring went by me at shoulder height, perfectly quiet. I could not find the anger again afterwards. I have looked.”
“My daughter asked whether it was alive. I said no. She said it was, for about four seconds. She is right and I was wrong, and I think about that most days.”
“Two hundred people stood in a parking lot in complete silence watching a doughnut of fog cross forty yards of air. Nobody filmed it. That is the part I tell people about.”
C.A.T.S.S.
Circular Aerial
Temporary Sculpture
Formation, translation and decay of a toroidal vortex discharged from a 55-gallon drum. A sculpture of air, held for a few seconds and then gone.
- Drum
- 22.5 × 33.5 in.
- Orifice
- 6 in. dia.
- Swept vol.
- 780 cu. in.
- Lifetime
- seconds
Plate I
The apparatus, in longitudinal section
Key
Parts
- A
Steel drum, open head. Use a new or reconditioned drum only — never one that has held flammable or toxic contents.
- B
Diaphragm: latex sheet 0.020–0.030 in., or a heavy shower curtain, clamped by the drum's own lock ring against the rim.
- C
Backing plate and cross-bar bonded to the centre of the diaphragm, spreading the load over the sheet.
- D
Bungee cords anchored forward on the body, drawn back, latched, and freed by a pin.
- E
Orifice, 6 in. diameter, cut in the fixed head; inner edge rolled, or fitted with a ring of round bar.
- F
Fog inlet, closed by a flap before discharge.
- G
Stroke δ of about 6 in. at the centre. Volume swept is roughly one third of δ times the head area, or 780 cu. in.
Translation
Speed of a thin-cored ring
U = ( Γ / 4πR ) [ ln (8R / a) − 1/4 ]
Kelvin, 1867. It assumes a thin core, a / R small. A discharged ring's core is not thin, so this gives the trend, not the number.
Sizing the orifice
A forming ring takes up circulation only while the slug of air ejected behind it is shorter than about four orifice diameters. Past that ratio the surplus leaves as a trailing jet and adds nothing to the ring. The slug has volume (π / 4) D² L, so setting L equal to 4D and solving for D gives
D = ( V / π )^(1/3)
where V is the volume the diaphragm sweeps. For the drum V is about 780 cu. in., giving D of about 6.3 in. The same rule on a 6 in. can with a 1 in. stroke gives about 1.5 in.
Notes
- 1
Circulation is imparted at the moment of discharge and thereafter conserved, apart from viscous loss (Helmholtz, 1858). A ring cannot be strengthened once clear of the lip.
- 2
Pull force rises with the area of the head, so with the square of its diameter: a 22.5 in. head has some fourteen times the area of a 6 in. one. Hand traction will not serve here, hence the bungee release at D.
- 3
The fog makes the ring visible but is no part of it. It must be brought to rest before discharge — a minute or so in a chamber of 7.3 cu. ft. — or the shear sheet is disturbed as it forms.
- 4
Decay proceeds by viscous diffusion of the core. As a grows the bracketed term falls and the ring slows, while R increases slowly. The end is a waviness about the circumference (Widnall, 1974).
- 5
Range is not calculated here. A ring of this size should carry a good many yards in still air, but the distance turns on discharge speed and on the stillness of the air. Establish it by trial.
Dimensions are nominal. Rounding the lip of the orifice matters more to the result than any other single detail of the build.