[SML] Snow in the UK?

[billn at peak.org]

> No....  They were both adamant that there was a device that was a
> cylinder that rotated around a lamp.

I suspect that they are misremembering.

Even with tiny holes, which would make the light dots very dim, the device
would have to be close to the projecting surface if you didn't want large
dots.

This effect is subject to the inverse square law. Pretend the lamp is a point
source for purposes of discussion. Let us assume the lamp is 3" from the
pinholes. Let the pinhole diameter be D.

At a distance of 3 inches from the cylinder, the dot size will be 2D. At 2
feet, it will be 9D. So if the pinhole is 1/32" diameter, the dots at 2 feet
will be 9/32" across. At 4 feet dots will be 9/16" across and at 8 feet they
will be over 1" across.

As the dots get larger, they get dimmer even more rapidly. When the dot
doubles in diameter, the light intensity is cut to 1/4.

You can get reasonably small dots by mounting tiny mirrors on a rotating
cylinder, then focusing a very long focal length instrument on it. Mount the
light as far from the cylinder as possible.

Unfortunately, the result will not look like snow or rain. At least it never
has for me.

Bill