362 SECTION MECHANICS. 



sun's rays is to be intensified by a number of lenses in a frame. He 

 proposes these apparatus as mere toys to work ornamental fountains, 

 but Belidor, by article 827, describes and shows a sun pump consisting 

 of a large metallic sphere fitted with a suction pipe and valve and a 

 delivery pipe and valve and occupied partly by water and partly by 

 air, the suggestion being, as in the case of Salomon de Caus, that the 

 heat of the sun in the day time expanding the air should drive up 

 the water into a reservoir, while the contraction of the air in the night 

 time should elevate the water by the suction pipe and thus re-charge the 

 sphere for the next day's work. In modern times, as we know, some 

 attempts to obtain practical motive power from the direct action of 

 the sun have been made, and notably by Mr. Ericsson.* 



The temptation to endeavour to bring into ordinary and commercial 

 use a machine of this character is very great. We were told by our 

 President in a lecture delivered by him to the British Association at 

 Bradford, that the solar heat if fully exercised all over the globe, and 

 supposing that globe to be entirely covered with water, would be 

 sufficient to evaporate per annum a layer fourteen feet deep. Now 

 assuming ten pounds of water evaporated from the temperature of 

 the air into steam by the combustion of one pound of coal (a much 

 larger result than unhappily we get in regular work), this would 

 represent an effect obtained from the sun's rays on each acre of water 

 equal to the combustion of 1680 tons of coals per annum, or about ninety- 

 two hundredweight of coal per acre per twenty-four hours, that is to 

 say, enough to maintain an engine of two hundred gross indicated 

 horse-power day and night all the year round. When, however, we 

 consider the effect of the sun, not upon the surface of water but upon 

 the earth, and deal with its power of producing heat-giving material, 

 that power compares very unfavourably with the results above stated, 

 and this no doubt arises, first, from the fact that the sun is 



* In the number of the " Revue Industrielle," of the 24th November last, page 455, are an 

 engraving and a description of the solar boiler of M. Mouchot, Professor at Tours. The 

 apparatus employed by M. Mouchot consisted of a framework shaped like the frustrum of a 

 cone, and mounted so that the axis could always be moved to point to the sun. The interior 

 of the framework was lined with mirrors, the diameter of the large mouth of 'the cone was 

 2 '6 metres, and of the base i metre, giving an effective area of sun's rays intercepted of 

 45 feet. The mirrors were placed at an angle of 45, and reflected the rays of the sun upon a 

 blackened copper boiler, placed within a glass envelope in the axis of the cone. It is stated 

 that on a very hot day as much as n Ibs. of water were evaporated per hour by this apparatus. 



