... steadily enough to keep the object-glass upon the black spot, and she had a great deal of trouble in the matter of focusing, pulling out and pushing in the smaller cylinder in a manner which showed that she was not accustomed to the use of this optical instrument. ... — The Captain's Toll-Gate • Frank R. Stockton
... midst of this titanic battle a huge disc appeared, carried by the gaseous clouds. It was a concave lens, like some powerful optical instrument. But instead of focusing beams of light, it reflected, not only light but all forms of energy. As the spheres attacked they were shattered into spores ... — The Whispering Spheres • Russell Robert Winterbotham