gems, glyptic, beads, archaeology, microscopy

It is not generally known how much the science of archaeology owes to the science of microscopy. In no branch is the microscope of more use than in the study of ancient beads, but to study them properly a microscope with first-class optical units and several attachments is necessary. The microscope that I use is rather bulky, and is fitted on a bench made from a lathe bed. This is not necessary, but is a great convenience, as the illuminant is on the same bench, and also the photographic camera. Although high resolution is not always a matter of the first importance, the frequent comparison of colour of small particles makes apochromatic objectives a great advantage; also they enable one to use an eyepiece x25 with comfort. I use a binocular body, not usually for binocular vision, although that. sometimes is an assistance, but generally with a x 6 compensating eyepiece in the left-hand tube, and a x 25 one in the right-hand tube. In this way the ~6 acts as a finder, an important matter when there are only a few minute chips of transparent glass mounted in balsam on the slide. I also use a double nosepiece. The slight amount of eccentricity got in this manner is corrected by a touch on the #crews of the substage centering fitting. For the great majority of my work I have a 16 mm. and 8 mm. objective on the double nosepiece, each fitted with a ring illuminator. This arrangement gives magnifying powers of about 60, 120, 250, and 500. In some cases when photographing, the flatness of the field is much inore important than the resolution, so, to correct this, I find that an iris diaphragm behind the objective is a great assistance. It also perceptibly increases the depth of focus. Over the eyepiece I have a tourmalin, which can be easily swung in and out. This I find a great advantage over a prism, as the latter is very apt to cause astigmatism, and even more frequently to cut down the field of view when photographing.