GB169495A - Improvements in or relating to mathematical demonstration apparatus - Google Patents

Abstract

169,495. Battey, A. F., and Pattison G. June 22, 1920. Teaching geometry.-Apparatus for demonstrating trigonometrical ratios comprise a circular frame of wood or other material bearing a circular scale of angles and mounted on a stand, a graduated radial arm pivoted at the centre of this scale, and means for projecting vertically any point of this arm on to an horizontal diametral graduated bracing of the circular frame. In one form, these means comprise a plumb-line hanging from a pin on the radial arm or on the upper part of the circular frame in the case of angles in the third and fourth quadrants. In a second form, shown in the Figure, these means comprise a graduated strip 6 of wood, celluloid, &c., pivoted at 9 to a slide 7 on the radial arm 5 and hanging vertically downwards under the action of its own weight in the case of angles in the first and second quadrants, and vertically upwards under the action of a counterweight attached to the end 8 of the strip 6 in the case of angles in the third and fourth quadrants, the edge of the scale on the strip 6 preferably lying in a vertical line through the pivot 9. To ensure accuracy in reading the position of the strip on the horizontal bracing 3, the scale on this bracing may be mounted on a mirror to eliminate errors of parallax, and the strip 6 may be made of transparent material, or the edge of the scale on the strip 6 may coincide with the edge of the strip or of a slot in the strip or with a wire stretched along such slot. To demonstrate sines and cosines, the distance between the pivot 9 and the centre of the circular scale mav be made equal to the radius of this scale, which is preferably ten divisions of the straight scales. To facilitate the demonstration of tangents and secants, and of cotangents and cosecants using complemental angles, the radial arm 5 may be provided with a graduated extension, a longer vertical strip then being pivoted to a pin sliding in a slot in this extension so that the edge of the scale on the vertical strip may be made to coincide with the end of the horizontal bracing 3. The longer strip may also be held horizontally so as to pass through the ends of the vertical diameter of the circular scale.