Numbers of delicate processes stand between the rough glass and the finished implement. The glass must be cut, ground, and curved exactly to the requisite design, which in itself takes many days of high mathematical computation; it must be smoothed and polished, cleaned with meticulous care, and adjusted to a nicety in the particular instrument for which it is fashioned. The difficulties and pitfalls are incalculable; from start to finish the glass obeys no fixed laws, but answers only to the skilled handling of the scientist and craftsman. 'Optical glass is the mule of materials', comments a recent writer with sincerity.
The absence of requisite labour for what was practically a new industry was a serious menace, and it is to the credit of Englishwomen that, as soon as the need for their services in this direction was made known, they stepped without hesitation into this unfamiliar and highly skilled industry. Their success therein is remarkable, and many, from such callings as high-class domestic service, kindergarten instruction, music teaching, blouse and dressmaking, have achieved a wonderful record in the delicate and highly technical processes of lens-smoothing and polishing and in the production of prisms of faultless polish and cut.
There is, I take it, no more interesting munitions development than in factories where these lenses and prisms are produced. The work is so fine and so delicate that one feels it might be more suitably transferred for manipulation to elves, or fairy folk, who might undertake the various processes standing at a large-sized toad-stool. But with the stern reality of war upon us, willing feminine fingers have had to be trained to handle these lenses, the smallest of which, when ranged in trays, resemble a collection of dewdrops, and the largest of which would easily fill the port-hole of an ocean-liner.
Optical glass when it comes into the workshop has the appearance of small blocks of rough ice of a greyish hue. These blocks are roughly sliced and cut into shape by a rotating metal disk charged with diamond dust. The prisms and lenses in their initial stage are then handed on to women, who complete the work on their surfaces. Each process has its particular lure for the interested visitor. You may watch the slices of glass being shaped into prisms by handwork against the tool; you may follow these embryo prisms through the various processes of smoothing and polishing until a small magnifying prism is obtained for use in a magnetic compass, or until a large prism is completed suitable for a submarine periscope. You may follow the creation of a lens from the roughing and grinding of the glass slices with emery, or carborundum, until the approximate shape is given, or you may follow a later process of sticking the smaller lenses on to pitch, so that they may form a single surface for smoothing and polishing.