A Heliostat for the Lecture Room
Rigge, William F., S.J.
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First Paragraph: A heliostat, that will hold a beam of sunlight as steady as if it came from a stereopticon fed by a self-focusing arc-lamp, is looked upon by the majority of professors of physics as ideal but quite unattainable. Such an instrument would seem to be either prohibitive on the score of cost, or impracticable, owing to the demand it would apparently make for a working knowledge of astronomy to insure its accurate adjustment and manipulation. Personal experience has convinced me that the heliostat above referred to is within the reach of every teacher of physics, if he has some mechanical skill in the use of tools and the elementary knowledge of astronomy which this article will explain in detail. On these conditions he can set up his instrument and adjust the beam of sunlight within a minute or two, without a knowledge of the correct time, or of its equation, or of the sun’s declination, that is, without consulting a time piece or an almanac.