FOCAL a.
Belonging to,or concerning, a focus; as, a focal point. Focal distance, or length,of a lens or mirror (Opt.), the distance of the focus from the surface of the lens or mirror, or more exactly, in the case of a lens, from its optical center. --Focal distance of a telescope, the distance of the image of an object from th…
FUNCTION n.
implicit function of x. -- Inverse trigonometrical functions, or Circular function, the lengths of arcs relative to the sines, tangents, etc. Thus, AB is the arc whose sine is BD, and (if the length of BD is x) is written sin - 1x, and so of the other lines. See Trigonometrical function (below). Other transcendental…
GAUGE n.
to the straight side of a board, etc. -- Printer's gauge, an instrument to regulate the length of the page. -- Rain gauge, an instrument for measuring the quantity of rain at any given place. -- Salt gauge, or Brine gauge, an instrument or contrivance for indicating the degree of saltness of water from its specific…