Popular Science Monthly 



517 



would Ikuo been reduced to a mere 

 cinder. If tlic amount of lieat received 

 is to be measured, tills radiation must be 

 checketl. A iieat Irap must be desij^ned. 

 One of the earliest instruments made for 

 that purpose was devised by the late 

 Professor Samuel Pierpont Langley, of 

 the Smithsonian Institution, somewhat 

 on the lines of a gardener's greenhouse. 

 His heat trap was simply a box provided 

 with a double glass pane and [lacked with 

 cotton to reduce loss of heat by radiation. 



successful if constructed on the principle 

 of the gardener's greenhouse and Lang- 

 ley's box. Mr. Frank Shuman has 

 given us a type of solar power plant 

 in which a thin film of water is heated 

 in a cast-iron trough surrounded by 

 window glass. So intense is the heat 

 impounded by the double glass that the 

 water is quickly raised to the boiling 

 point (two hundred and twelve degrees 

 Fahrenheit) or very near it. 



After the water is brought to about 



r 



^ 



^'TT^^ 



The water which is heated by the parabolic reflectors is stored in well-insulated tanks. A 

 low-pressure steam-engine was designed by Mr. Shuman which would take this hot water 

 and use it to drive a piston even though the pressure gained was only four pounds absolute 



The layer of air between the two sheets 

 of glass served as a heat insulator, and 

 the glass itself [prevented the heat which 

 enlered the box from escaping. On 

 Pike's Peak, where the thermometer 

 recorded fifty-nine degrees Fahrenheit, 

 the temperature in the box rose to two 

 hundred and thirty-five degrees. Had 

 he succeeded in trapping all the heat, 

 which is practically impossible, he might 

 have obtaineil enough to melt solder. 

 Since Langkn's time, experiments con- 

 ducted by Mr. C. C. Abbott of the 

 Smithsonian Institution have given 

 much better results. 



These facts having long been known, 

 it has occurred to more than one inventor 

 that a solar power plant might prove 



the boiling point in the trough, it is con- 

 veyed to a steel storage-tank in the in- 

 ventions of Mr. Shuman. That tank is 

 not simply an enlarged covered pot, but 

 a vessel so constructed that as little heat 

 as possible can escape from the water 

 within. Just as we keep ourselves warm 

 in winter by wearing clothes to prevent 

 a too abundant radiation of our bodily 

 warmth, so Mr. Shuman swathes his 

 storage-tanks in an insulating material 

 which keeps the water hot for many 

 hours. 



But how can an engine be driven with 

 nothing but hot water? Mr. Shuman 

 l)erforms the feat by the paradox of 

 making the water boil without flame 

 after he has stored it. Thus he generates 



