McArthur field microscope, $5.

The McArthur 'field microscope' is one of my more unusual finds, and I've never seen anything like it before. As it turns out, a field microscope is designed to be used by scientists who have the need to take a high-quality microscope out into the field, but can't afford the bulk that a regular laboratory microscope would cause. On the surface, it doesn't appear that making a miniature microscope would be that much of a trick. Apparently, though, there's much more to it than there appears to be, because Dr. McArthur spent many years designing this microscope, actually making many of his prototypes out of wood so that he could more easily modify the design until he got it just right.

To give you an idea of the weirdness of this instrument, consider the fact that to see what is on the microscope slide, you must look into the eyepiece on the other side of the microscope. To keep within the limits of the small body, McArthur designed a 'folded optical prismatic system' that uses prisms to bend the light twice before it gets to the viewer's eye. As light enters the instrument from above, by means of the microscope's own mirror or from an electric lamp, it then passes downward onto the specimen on the slide. Since the objective lens (the lense that actually magnifies the image) is below the specimen, the setup is so far pretty much like a conventional microscope turned upside down. But after the light passes through the lens, the image is then reflected by the prismatic system through a tube along the bottom of the microscope, where another prism at the other end bends the light upward to the eyepiece, where it's viewed by the scientist.

Okay, so it's not really that important for you to know exactly how this microscope works. But I didn't buy this just because it's a miniature microscope. I bought it because it was obviously an incredibly well made, carefully engineered and very precision scientific instrument, which just happened to be a compact field microscope. The very first thing that struck me when I saw this - and before I really knew what it was - is that it's a small piece of very specialized scientific equipment. As you pick it up and examine it, you notice that it's very heavy, and is so intricately made that it seems to have been machined from a solid piece of metal - by hand. Another good indicator is that it's made in the U.S.A., in London, Wisconsin.

As I researched this microscope, I found what I might have figured all along, which is that people out there actually collect these field microscopes. When you think about it, they're actually perfect candidates for collectors, because they're small, intricate, carefully crafted and represent a very distinct segment of science.

This little McArthur field microscope sold on eBay for $865.