NO. 5 UTILIZING HEAT FROM THE SUN ABBOT 3 



the yearly adjustment is unnecessary and the daily motion can be 

 allowed for by merely rotating the parabolic cylindric ray-concen- 

 trating mirror about an axis coincident with that of the boiler tube 

 at the rate of 15 ° per hour. In this arrangement the boiler tube may 

 be firmly fixed. This, with the simplicity of the mechanical driving 

 of the mirror, renders this arrangement preferable to all others for 

 most purposes. The mirror may be driven by clockwork, or, if 

 electric facilities are available, still better by a 60-cycle synchronous 

 motor through a worm and wheel. 



I have used both types of driving. Our solar cooker on Mount 

 Wilson, having been built long ago, is cumbersome. It has a heavy 

 mirror, 8 feet wide by 12 feet long. I attached to the mirror a grooved 

 wheel 30 inches in diameter coaxial with the lower trunnion of the 

 mirror. A steel wire in the groove of the wheel supported a weight 

 of about 200 pounds, sufficient to rotate the mirror toward the west. 

 Through a second steel wire wound in the groove in the opposite 

 sense, the weight also drove a clockwork. This clockwork train 

 ended in a fly vane. A long hand rotated with the central shaft and 

 once in each revolution was stopped by a displaceable pin. The long 

 hand would make a full rotation in about 3 minutes. A common 

 alarm clock was provided with a wheel of 12 pins on the back of 

 its hour shaft, and these pins, acting through a lever escapement 

 displaced the stop-pin once each 5 minutes. Hence the mirror moved 

 intermittently as governed by the alarm clock, and was never more 

 than 1 minute from its proper position to focus sun rays upon the 

 heater tube. Still simpler clockwork contrivances may be used to 

 drive smaller mirrors for solar heating devices. 



DOMESTIC WATER HEATERS 



Those who have visited Florida or southern California may know 

 of the roof water heaters which are used considerably for providing 

 hot water for bath and other household purposes. A shallow depres- 

 sion is let into the south roof exposure, and lined with blackened 

 sheet metal. Therein is supported a blackened grid of pipes like a 

 steam radiator. The boxlike depression is covered tightly with glass 

 windows. Water circulates through the piping, and thence to a 

 reservoir at a higher level within the house. Such a system acts by 

 gravity like the water heater system of a cook stove. If the reservoir 

 is well insulated from heat losses and the location is relatively cloud- 

 less and never freezing, such a system is found to be very useful 

 for furnishing hot water both day and night, without maintenance 



