Parts from rods

Phase III - Preparing the parts made from metal rods

Draw a rod

While the body plates and mount gave Leeuwenhoek some latitude for variation, a screw rewarded regularity.

Four tools had to work together: drawplate, drill, tap, and die.

A typical iron or steel drawplate has several holes of regularly varying diameter. Unfortunately, no one has precisely measured the diameters of the rivets and screws of Leeuwenhoek's surviving microscopes to know whether he used the same tools for all the holes in a given microscope. In any event, we don't have enough microscopes, 11 out of 271, to see any similarities among microscopes.

Questions about the surviving microscopes:

• On a given microscope, were all the screws the same diameter?

• Were any of the screws the same diameter as the rivets?

• Indeed, were all of the rivets the same diameter?

The answers will tell us whether Leeuwenhoek made a batch of rivets separately from a batch of screws. Testing the silver of all the parts for purity may also reveal a pattern indicating his working methods.

He could have heated and pounded the silver until it was close to a rod. He also could have heated it until it was molten and then poured it into a cast in the shape of a rod. By drawing that through successively smaller holes, reheating as necessary, he made uniformly smooth rods of the appropriate diameter.

Cut the rivets and the turning knob

No one has measured the thickness of the body plates of the surviving microscopes. The profile views of the eleven show the bulge on each side, so the plates together were thinner than the lenses. Van Zuylen measured the thickness of the lenses; they range from 0.65 mm to 2.75 mm.

The rivets were not much longer, depending on how much effort Leeuwenhoek was willing to put into trimming them. After he cut them with a chisel or shears, they were so small that Leeuwenhoek must have used tweezers and perhaps even a low-powered magnifying glass to manage them.

If he cut them into, let's say, 4 mm sections and planned on putting six into the body plates and using one as the specimen pivot knob, he needed only 28 mm of rod, a couple of inches.

Cut the four screws and pound three screw handles

He used a chisel or shears to make the individual screws. First, he would have heated it, and enough heat would remain for a few hammer whacks to at least begin shaping the handle. The image on the right (click to enlarge) show the hammer marks as well as smooth edges that have been filed.

Make four screws; one is the specimen pin

He could have cast the screws but he more like used a die. He clamped the rod by its handle, standing straight up. He applied some oil to the rod. Then he positioned the die probably already locked into what we now call a tap wrench. That's another of those words from the 19th century that the Industrial Revolution brought to the English vocabulary. There is nothing in his letters about one, but if he made his own screws, he either used a tap or perhaps cast them. If he didn't use a tap wrench, the lathe he used for grinding glass may have worked. The excess silver rimming the empty hole on the 68x silver microscope shows what came out of the hole and why tapping screw holes involved oil. Today, tap wrenches make it easy to turn a little in both directions, so that the excess metal can work its way out of the hole while he was tapping it.

In the absence of actual measurements of the screws, a rough visual proportion seems to be 50:7:5:2, in other words,

• a positioning screw about 50 mm (~2 in) long

• a shorter focusing screw, 15 mm

• a slightly shorter pin screw, 10 mm, with a knob

• a very short braking screw, 5 mm, with a thin nut

If he used the same rod for the screws for just one microscope, he needed at most a four-inch rod. It would not be surprising to learn that he made a couple dozen screw and rivets at the same time, enough to make several microscopes

Leeuwenhoek needed a drill, a word he used, or perhaps a punch, the same size as the hole in the draw plate that made the rivet holes.

Attach the turning knob to the specimen pin

The image on the right (click to enlarge) shows what looks like a regular rivet driven through a hole drilled into a slightly flattened part of the specimen pin.

For that precise a flattening, Leeuwenhoek heated the silver and used a very narrow hammerhead to tap the rod. Then he drilled the hole and drove the rivet through it. A bit of the rivet protrudes from the other end, so the rod was either clamped or laid on an anvil covered on a bit of soft material such as leather.

The knob itself looks like a short section of rod with flat ends that was heated and squashed a little. Further testing would reveal whether it was attached by solder.

Late in his career, Leeuwenhoek mentioned soldering in two letters. On February 24, 1694 (AB/CL 133), he wrote to the Royal Society:

I took a glass Tube about the length and thickness of fig. 2, AB; on to this, by means of a copper blow-pipe, such as is used by Gold and silversmiths and with which they solder small jobs, ...

The following summer, August 18, 1695 (AB/CL 154), he wrote, again to the Royal Society:

This being so, I take a short Silversmith's Blow-tube to Solder with, and in order not to injure my eyesight I put a pair of Spectacles on my Nose ...

In both letters, he was speaking of using the smithing tools for glass blowing, but he clearly had them available.