A Peek in the Closet

Instruments for Natural Philosophy

In February 1975, Deborah Jean Warner, a Curator of Physical Science at the National Museum of American History, called me to ask if Kenyon had any historical physics teaching apparatus. I looked around my office, and reeled off the names of four or five good pieces of apparatus that I was using in my lectures. The next month I was at the Smithsonian, exploring the collection and photographing some of it in black and white and in color. Since then, I have visited and photographed nearly seventy collections of early physics apparatus. This web site displays pictures of about 1850 pieces of apparatus, along with text and references.

The Eyes Have It

Eye Cells as Light Pipes

The retina is at the rear of the eye and includes the light-sensing cells called photoreceptors. But across most of the retina, the photoreceptors are obscured behind three or four coats of additional retinal cells–networked neurons–and a carpet of cellular cables to the brain. Apparently, the retina processes an image by blurring it first. Biologists reference this odd “design” to illustrate that nature’s creations are not all so “intelligent.” Vision scientists have just tried to make sense of how it works as well as it does.

Size Matters

Abraham Lincoln was once asked, “How tall should a man be?” “Tall enough that his feet reach the ground,” was his reply.

Building A Shrink Ray? Consult This Grisly Physics Paper About Exploding Horses

Making something giant-sized looks cool in science fiction. Seeing it basically disintegrate under the strain of its own weight wouldn’t look nearly as cool. Okay, maybe it would. But it wouldn’t make for an interesting fight for the protagonist.

The “grisly” paper is On Being the Right Size by J. B. S. Haldane.

An insect, therefore, is not afraid of gravity; it can fall without danger, and can cling to the ceiling with remarkably little trouble. It can go in for elegant and fantastic forms of support like that of the daddy-longlegs. But there is a force which is as formidable to an insect as gravitation to a mammal. This is surface tension. A man coming out of a bath carries with him a film of water of about one-fiftieth of an inch in thickness. This weighs roughly a pound. A wet mouse has to carry about its own weight of water. A wet fly has to lift many times its own weight and, as everyone knows, a fly once wetted by water or any other liquid is in a very serious position indeed. An insect going for a drink is in as great danger as a man leaning out over a precipice in search of food. If it once falls into the grip of the surface tension of the water—that is to say, gets wet—it is likely to remain so until it drowns. A few insects, such as water-beetles, contrive to be unwettable; the majority keep well away from their drink by means of a long proboscis.

Expanding My Bandwidth

As any regular reader knows, I purchased a movie camera last year, which allows me to film movies in slow motion, covering actions with frequencies out to perhaps several hundred hertz — normally film at 420 fps, but can go to 1000 fps. This year, I went in the other direction. I bought an attachment for my DSLR that allows me to take time-lapse sequences, which I can then stitch together.

Here’s an example from last night. The weather forecast was for late-afternoon thunderstorms, but unfortunately for this demonstration they passed to the west of me on their way into Pennsylvania. We did get some rain just after dark, and this is the development of that storm system, shot at 30-second intervals over the course of about three hours.

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The attachment is called an intervalometer, which a pedant (who, me?) will note is incorrect. It’s not a meter of any sort — it’s not measuring anything. It merely sends a trigger signal to the camera at a programmable interval.