What's the shape of a falling raindrop?

January 23, 2013 7:17 PM

"When you run molten lead through a sieve and let it fall into a water tank far below, surface tension forms the lead drops into almost perfect spheres." The first purpose-built shot tower was built by William Watts of Bristol, UK, in 1782. America built its first shot tower in Philadelphia in 1808. The tallest shot tower ever built (but not the first in Australia) still stands in the center of Melbourne though now underneath a glass roof. As less costly methods of making shot were discovered these towers closed up shop, some not until the late sixties. Many of these towers have found new purposes as historical sites, art galleries or simply mysterious links to the past.

Read more about how we got buckshot

- Up a Shot Tower from Strand Magazine, 1891
- Gravity Molds Shot in a Modern Tower from Popular Science, 1944
- discussion of the manufacturing process (pdf) from Shotpeener magazine
- History of Baltimore's Phoenix Shot Tower, the tallest building in the US until the Washington Monument was built
- A paper on Baltimore's shot tower, from 1924 with a poem and illustrations
- The Ghost of New York, a story about Youle's Shot Tower, built in the early 1800's in Manhattan
- other shot tower links & shot nerd discussions & shot tower math

posted by jessamyn (42 comments total)

I had no idea. Thanks jessamyn. Thanks Metafilter!!
posted by Mr.Me at 7:23 PM on January 23 [1 favorite]

Oh, hey, I've seen that Melbourne shot tower! Everyone there knew it was some kind of significant local building, but nobody knew what it had been used for. Thanks for the explanation.
posted by Mars Saxman at 7:26 PM on January 23

That's really rather cool and something I'd never heard of before. BOTW!
posted by arcticseal at 7:27 PM on January 23

Yup, totally love shot towers. Made a special trip to the one in Baltimore. Dubuque is next. (And I might even visit the Mississippi River Museum while I'm there.)
posted by wormwood23 at 7:33 PM on January 23

Oh, hey, I've seen that Melbourne shot tower! Everyone there knew it was some kind of significant local building, but nobody knew what it had been used for. Thanks for the explanation.
posted by Mars Saxman at 3:26 AM on January 24 [+] [!]

Erm, but it's called the Shot Tower.
posted by awfurby at 7:33 PM on January 23 [8 favorites]

This is so cool! After reading these, I really wanted to see it in action -- here's a quick video showing a shot tower in use.
posted by ourobouros at 7:34 PM on January 23 [3 favorites]

it's called the Shot Tower.

The reason I made this post is because I saw an AskMe about stuff to do in Baltimore and someone said Phoenix Shot Tower and I wondered "What is that?"
posted by jessamyn at 7:40 PM on January 23 [2 favorites]

Incidentally, there is a shot tower less than a mile from recent FPP subject Taliesin.
posted by Jpfed at 7:42 PM on January 23

Woah, weird. I've heard the phrase "shot tower" enough in my life that it sounds familiar but I had absolutely no idea what it was. What a weird, random industrial manufacturing process. So simple!
posted by Nelson at 7:46 PM on January 23

After reading your comment, Jpfed, I just figured this out: we have two shot towers here in the greater SW Wisconsin/NE Iowa metro area because of all of the lead mining. The mines have been closed for a long time (100s of years maybe, decades at least) but the towers are still here. Neat!
posted by wormwood23 at 7:48 PM on January 23

Shot towers still exist! Indeed, anybody who knows Hull in England will know the "Shotwell" tower by the river. It's not a lovely old building, but it is a real working shot tower. (And thanks to my dad I've known about this method since I was a kid, but thought at first he was having me on.)
posted by Jehan at 7:55 PM on January 23

The tallest shot tower ever built (but not the first in Australia) still stands in the center of Melbourne
Hmm - "This 160 metre shot tower in Reilly Street (now called Alexandra Parade) and its associated factory was built for Richard Hodgson in 1882 to manufacture lead shot. The tower is all that remains today and is probably the tallest shot tower in Australia."
posted by unliteral at 8:08 PM on January 23

Reminds me of my time living in Bridgeport, CT, exploring some of the abandoned factories there including the Remington Shot Tower, which of course contributed to Bridgeport being nicknamed "the Arsenal of Democracy" back in the day.
posted by entropone at 8:10 PM on January 23

With the dreams and the eccentric inventing and the tragic-ironic twist in the end, Wiliam Watt's story is like an Industrial Revolution era fairy tale...



I'm surprised he only got the rough equivalent of £700K ( I assume the valuation is out of date so maybe it's more like a £1M+) in today's money for his company though. sounds like he got a bad deal
posted by Bwithh at 8:13 PM on January 23

Okay, I see that '160 metre' is ridiculous, it's 160 feet. So, it comes up short by 5 feet. Carry on as you were.
posted by unliteral at 8:18 PM on January 23

That cool British Pathe video clip ourobouros posted above has a different origin story - lead dripping off a church roof on fire gave someone the idea ? ( sounds unlikely). It also has a terrible joke at the end
posted by Bwithh at 8:25 PM on January 23

I'm embarrassed to realise how many times I've walked under the Melbourne Central Shot Tower without ever feeling even tiniest niggle of curiosity as to what it was. Thanks Jessamyn for bringing a bit of wonder & sense of living history to my daily commute.
posted by Wantok at 8:32 PM on January 23

Erm, but it's called the Shot Tower.

Well, sure, but first you have to know what a "shot tower" is.... which I now do, thanks to this post.
posted by Mars Saxman at 8:33 PM on January 23 [1 favorite]

Here's some info on and photos of the Selby Shot Tower in San Francisco, CA. Howard and 1st, 200' tall, 1870. I was curious because we have a Shotwell street too, which lends its name to a fine drinking establishment. But it's a few miles away.
posted by Nelson at 8:47 PM on January 23

I like that last link:
Powered by the sauerkraut fermentation process, the piece features miniature robots that scoot around, making abstract graphite drawings.

Some people say that sauerkraut fermentation processes shouldn't be used to power art-making by miniature robots. But I say "why not? Did you have a better use for your sauerkraut fermentation processes?"
posted by twoleftfeet at 8:47 PM on January 23 [3 favorites]

The raindrop becomes an arc, or bow.
posted by Mblue at 8:53 PM on January 23

IIRC, there was a shot tower in Little House in the Big Woods. Bullets meant it wasn't a girl's book.
posted by Alvy Ampersand at 8:55 PM on January 23

Was this here before? Acoustic Levitation.
posted by Splunge at 9:32 PM on January 23 [1 favorite]

And they're getting all hot and bothered about 3D printing of gun stuff. Ain't nothing new under the sun, boys.
posted by Devonian at 9:45 PM on January 23

Why did we ever think that drops of rain look like this or this or this?

Drops of rain become spheres of liquid, because surface tension, equally balanced, produces spheres.

So why do we think that a drop of rain should have a distorted shape, a sphere with a cuspoidal top?

Is it because of tears? Is it because a tear is a drop of water that leaves the eye, perhaps initially sphere-like, leaving a trail of previous tear liquid above, inducing a cuspoidal top to the tear? When I cry, do I not make a sphere?
posted by twoleftfeet at 10:33 PM on January 23

I love "Engines of Our Ingenuity" (transcript in the first link) and catch it most days during drive time. Great post.
posted by Burhanistan at 10:40 PM on January 23

Shot tower shout out.
posted by twoleftfeet at 10:51 PM on January 23

Hey, I had my senior BFA show in the fort Hayes Shot tower gallery. Neat!
posted by Jezztek at 12:18 AM on January 24

Prince Rupert's drops are not spheres, however.
posted by Segundus at 1:13 AM on January 24

There's one in Crane Park, near Twickenham.

It's on the site of what was the Hounslow gunpowder works which exploded at least 55 times, most recently in 1915.
On 11th March 1758 the explosion was so big it was heard in Reading, which is about 30 miles away.
They closed up shop in 1927, leaving behind blast mounds, sluice gates, grinding wheels, torn and shattered wreckage and a relatively intact shot tower.

The Shot tower itself was built in 1826 and is relatively small (for a shot tower) at only 25 metres tall.
It was refurbished in 2004 and is currently used as a base for the conservation team of the local wildlife reserve which replaced the powder works.

Also, I got married there two years ago.
posted by Just this guy, y'know at 2:32 AM on January 24 [1 favorite]

As less costly methods of making shot were discovered these towers closed up shop

I know you were talking about lead shot, but I'm pretty sure shot towers are still in use - in Germany anyway. I saw a documentary a while ago on a German company that makes tiny glass beads using a shot tower. The beads (or shot) don't fall into water, but solidify into a pretty perfect sphere as they fall through the air. The tiny (and I mean grain of sand size) glass beads are mixed with white road marking paint to reflect back car headlights (cat's eye-style) and increase road safety. They were filtered by size using a nylon, stocking-type mesh and those that were too big were melted down again and re-sprayed out of the to of the tower.

Have the feeling it was a new product the firm were trying to market and not sure it took off. Can't find name of the firm.

So why do we think that a drop of rain should have a distorted shape, a sphere with a cuspoidal top?
In a zero G, windless environment, it makes sense that any liquid would form into a perfect sphere because of the surface tension but a falling raindrop is subject to unidirectional air resistance so it seems logical that it would not form a perfect sphere (to me anyway).
posted by guy72277 at 2:51 AM on January 24

Raindrops are almost never tear-shaped. It's a popular misconception.

Here are the usual raindrop shapes for drops starting at 1 mm. (From this site)

Rain drops usually look like hamburger buns, not tear drops.

My guess is that people recognize rain drops from the ones on windows, or really do associate them with tear drops. A drop of water on a surface behaves differently than a free-falling drop.
posted by twoleftfeet at 3:07 AM on January 24

> As less costly methods of making shot were discovered

How is shot made now? It seems hard to imagine a cheaper method than "pour lead and let gravity do it's thing".
posted by adamt at 3:09 AM on January 24

Not to be confused with hose towers, which are also ornate 19th century buildings seemingly too tall and narrow for practical use, found in mill towns.
posted by Slap*Happy at 5:02 AM on January 24

Genius: Sometimes it seems so simple and obvious. The way the guy built his house and gambled on his idea is fantastic.
posted by marienbad at 5:11 AM on January 24

Thanks Slaphappy. I think you've answered a question I didn't ask. There's a building near me, now a brewery, with a tower that makes no sense (they make a nice dark beer though). Now I suspect it's a hose tower.
posted by Goofyy at 5:19 AM on January 24

I wonder if the metal sieves at the top of the towers ever get clogged? Do they ever form lead "icicles" on the underside? Perhaps at the perimeter of the sieve?

My father told me about shot towers when I was a child. I haven't thought about them in many years.
posted by Tube at 5:55 AM on January 24

How is shot made now?

As near as I can tell there is a newer method for making lead shot called the Bliemeister method which Wikipedia says is done this way "metered molten lead is dropped approximately 1 in (2.5 cm) into hot water, rolled along an incline and then dropped another 3 ft (91 cm). The water temperature controls the cooling rate of the lead, while the surface tension brings the ball into a spherical form." I went fishing for a decent link or two about this and couldn't find one. Non-lead shot, some of it anyhow, is made using wire which is chopped up and then pressed. Here is a patent that sort of explains it.
posted by jessamyn at 7:14 AM on January 24 [1 favorite]

Also: Drying Towers.

About a hundred feet high. We used a similar building (on Okinawa) to dry parachutes: hose them down to get the mud off, maybe have to use a brush on the harness and release ass'ys. Hang 'em up and blow warm air under them overnight. T-10s were only 50' long, counting the suspension lines, but the G-11s were about a hundred.
posted by mule98J at 8:11 AM on January 24

Giving directions to tourists exploring downtown Baltimore almost invariably involves saying "you'll see the shot tower" at some point.
posted by HumanComplex at 9:52 AM on January 24

The tallest shot tower ever built (but not the first in Australia) still stands in the center of Melbourne though now underneath a glass roof.

It's not just in the middle of the city, or under glass. It's in the middle of a shopping centre entirely enclosed in the outer building. From the outside you'd never know it's there. Also, lots of the buildings are joined together by walkways and undergrounds etc, so you can be wandering around through various shops just drinking the amazing coffee and looking at stuff then suddenly, bam. There's a huge brick building right in the middle just hanging out enjoying the air con like everyone else.

That's what happened to me on my first visit to Melbourne anyway and it made quite an impression.
posted by shelleycat at 12:16 PM on January 24

Alvy Ampersand: "IIRC, there was a shot tower in Little House in the Big Woods. Bullets meant it wasn't a girl's book."

I don't think so. Pa made his own bullets using a mold. Shot was available in town, but I don't think they said anything about its manufacture.
posted by Chrysostom at 6:28 AM on February 22