Measures for Progress: A History of the National Bureau of Standards

OPTICAL GLASS AND OPTICAL INSTRUMENTS 189
After the optical glass mixture has gone through the melting process and solidified under
slow cooling, the pot is broken away from the 1000-pound melt. The glass cannot be
removed from the pot in a molten or plastic condition or bubbles and cords will form.
Although the chemical composition of good optical glass had been mastered by World
War I, a satisfactory pot material had not, and the special kaolin-clay mixture developed
by the Bureau proved a real contribution to the industry.
manufactured in this country on a large scale for the first time. This was
particularly true of binoculars, but also included periscopes, range finders,
military and naval gun sights, bomb sights, and aviators' goggles. Important
assistance was given as well in the manufacture of mu scales for military
binoculars and in the development of the 37-mm gun sight, the panoramic
machine gun sight, a new tank-gun sight, and a periscopic alidade.
The alidade, an angle-measuring device, illustrated how our armed
services acquired some of their new optical instruments. The AEF sent
back a French model, asking the Army Engineers to copy and supply it to
our forces. The Bureau took it apart and from the data supplied, the
Engineers prepared the blueprints for an instrument manufacturer. Samples
of the American-made alidade then came back to the Bureau and with a
few minor changes the device was approved for production.73
An interesting adaptation of peacetime optical research to wartime
needs occurred in the case of military photography. Some years before the
war, the spectroscopy section had carried out an extensive program of measur-
"War Work," p. 188.