NO. 5 UTILIZING HEAT FROM THE SUN ABBOT 5 



In this embodiment the outer of these two glass cylinders may be 

 itself surrounded by evacuated space. This makes a very beautiful 

 and highly efficient, quickly heated oven of small capacity. For a 

 large installation it is better not to use the liquid directly as the 

 absorbing medium, but to contain it in a blackened copper tube, itself 

 surrounded by a vacuum jacket of glass. This arrangement lends 

 itself to a more robust connection of the heater tube to the oven 

 jacket. Liquid may then be supplied to give a large capacity for heat 

 and to heat a plurality of ovens. 



To fix approximately our ideas of the size of an outfit for solar 

 cooking, I give the following figures. In clear sky conditions one 

 may depend on from 1.2 to 1.4 calories per square centimeter per 

 minute of energy in the solar beam. Using the lower of these figures 

 we have still to encounter the following losses. Mirror reflection 

 82 percent, vacuum jacket transmission, if direct to liquid, about 

 89 percent, if through a blackened metal tube to liquid about 80 per- 

 cent. Hence there remains about 0.79 to 0.87 calory per square 

 centimeter per minute. The maximum temperature which a mirror 

 will maintain in an oven depends on the rate of loss of heat. The 

 time required to approach that temperature depends on the capacity 

 of the oven and its surroundings for heat. These variables I cannot, 

 of course, predict without specifications. But it may safely be said 

 that, with good design, a mirror of 4x8 feet surface will keep two 

 ovens of ordinary size hot enough to bake biscuits well, by night as 

 well as by day, in any fairly cloudless regions in the temperate zones. 



TOY SOLAR COOKER 



I have constructed a toy cooker with a mirror surface of 15x20 

 inches to warm an oven 3^ inches square, 2^ inches high, and insulated 

 by 3 inches in thickness of glass wool. It requires about an hour to 

 heat the oven to about 130 C. above surrounding temperatures, and 

 the oven bakes cakes 3 inches square very nicely in a half hour. 



SOLAR WATER DISTILLING 



Distillation of water may be very efficiently done with solar heating. 

 The arrangement of the mirror is similar to that just described for 

 cooking purposes. In this case, however, the elongated vacuum 

 jacket, like a thermos tube except that it is not silvered within, is 

 supported in the focus of the mirror with its open end at the bottom, 

 and its closed end extending a foot or more above the top of the 

 mirror, which rotates on rollers bearing the hollow trunnions of the 



