The term sweet spot is used in describing that point or region of a tennis racket where the ball should be hit for optimum results. There are several definitions of this term, each one based on different physical phenomenon.

The collimator consists of a convex lens at the end of a tube, with a vertical slit, or a pair of cross-wires, in the focus; the telescope is a common telescope with a positive eye-piece, and a pair of cross-wires in the focus of the eyepiece.

I began also to feel very hungry, as not having eaten for twenty-four hours; and worse than that, there was a parching thirst and dryness in my throat, and nothing with which to quench it.

So far, I have only pieced together a partial account of the incident.