320 



NATURE 



\August 2, 1888 



silver on the under side. The frame consists of a light 

 structure of wrought iron or steel, provided with trans- 

 verse ribs as shown by the illustration, each rib being 

 accurately bent to a parabolic curvature whose focus 

 coincides with the axis of the cylindrical heater. It needs 

 hardly be stated that the mirrors supported by the said 

 transverse ribs continue from side to side of the frame, 

 which accordingly resembles a parabolic trough whose 

 bottom is composed of mirrors. It will be readily under- 

 stood that this trough with its bent ribs and flat mirrors 

 forms a perfect parabolic reflector, to which a cylindrical 

 heater, as stated, may be attached for generating steam 

 or expanding the gases intended to actuate the piston of 

 the motive engine. Regarding the mechanism for turning 

 the reflector towards the sun, engineers are aware that 

 various combinations based on the principle of the 

 " universal joint " may be employed. 



Concerning previous attempts made in France to utilize 

 solar energy for mechanical purposes, it is well known 

 that practical engineers, having critically examined 

 Mouchot's solar engine, which M. Tellier proposes to 

 supersede, find that it is incapable of developing 

 sufficient power for any domestic purpose. Again, the 



investigations carried out by order of the French 

 Government to ascertain the merits of Mouchot's inven- 

 tion show that irrespective of the great expense of silver- 

 lined curved metallic reflectors for increasing the insuffi- 

 cient energy of direct solar radiation, these reflectors 

 cannot be made on a sufficient scale for motors having 

 adequate power to meet the demands of commerce ; nor 

 is it possible to overcome the difficulty of rapid wear of 

 the delicate silver lining of the metallic reflectors conse- 

 quent on atmospheric influence, which after a few hours of 

 exposure renders their surfaces tarnished and ineffective 

 unless continually polished. A glance at the accom- 

 panying illustration (Fig. 1) shows that the reflector con- 

 structed for my sun motor differs altogether from that 

 originated by Mouchot, which Tellier's apparatus, tested 

 at Paris, was intended to displace. 



Description of the Illustrated Reflector. 



(1) The mirrors which reflect the solar rays are devoid 

 of curvature, being flat narrow strips of ordinary window- 

 glass, cut to uniform width and length, perfectly straight. 



(2) The under sides of said strips are coated with silver 

 by a process which prevents the action of the sun's rays 



from destroying the silver coating as in ordinary looking- 

 glasses. 



(3) The mirrors supported by the bent metallic ribs 

 extending from side to side of the parabolic trough, are 

 held down by the heads of small screws tapped into the 

 ribs. Thin slats of wood may be introduced between the 

 mirrors and the ribs — an expedient of some importance 

 in localities where the reflector is exposed to high winds. 



(4) It needs no explanation that the reflecting surface 

 of the mirrors cannot become tarnished by atmospheric 

 influence, since the bright side of the silver coating is 

 permanently protected by the glass ; hence it will be only 

 necessary to remove dust from the mirrors, an operation 

 readily performed by feather brushes secured to light 

 handles of suitable length. 



(5) The frame of the reflector, being composed of rolled 

 bars of iron or steel, requires no finish, excepting the top 

 of the transverse ribs, which must correspond accurately 

 with a given parabolic curvature. It should be observed 

 that the needed accuracy is readily attained by a cutting 

 tool guided by a bar of proper form. 



(6) Regarding cost of construction, it will suffice to 

 state that manufacturers of glass, both in the United 



States and Germany, supply the mirrors, cut to exact size 

 and silvered, at a rate of 60 cents, per square foot, the 

 weight being 106 pounds per 100 square feet. Conse- 

 quently the cost of the reflector and heater for the sun 

 motor will not much exceed that of a steam boiler and 

 appurtenances, including chimney. The cost of the 

 engine apart from the reflector, will not be greater than 

 that of an ordinary steam-engine. 



(7) With reference to durability, it will be evident that 

 the light metallic frame with its mirrors, and a heater 

 acted upon only by reflected solar heat, will last much 

 longer than steam boilers subjected to the action of fire, 

 soot, and corrosion. 



Let us now briefly consider the distinguishing feature 

 of the sun motor — namely, the increase of the intensity of 

 the sun's radiant energy by parallel rays andyfo/ reflecting 

 surfaces permanently protected against atmospheric in- 

 fluence. It has been supposed that the lens and the 

 curved reflecting surface, by converging the sun's rays, 

 could alone increase the intensity of radiant heat. But 

 Newton's demonstration, showing that the temperature 

 produced by solar radiation is "as the density of the 



