.18 



Popular Science Monthly 



steam which can lie used in an cnj^'ine 

 of suitable desip;n. It must not he su|)- 

 posed that he discovered the paradox, 

 nor that he is the first to utilize it in a 

 practical wa>'. 



When Tyndall in one of his most bril- 

 liant writings defined heat as "a mode 

 of motion," he meant that the infinitesi- 

 mal molecules of which all matter is 

 composed are in a state of vibration. To 

 understand 

 his definition 

 we must imag- 

 ine the mole- 

 cules of all 

 bodies, even of 

 so cold a mass 

 as a block of 

 ice, moving 

 about at a 

 high velocity. 

 As soon as the 

 temperature 

 of the body is 

 raised, its 

 molecules vi- 

 brate faster, 

 collide with 

 one another, 

 and are made 

 to move in 

 longer paths. 

 Thus the phe- 

 nomenon of expansion under the inllueiice 

 of heat is produced. When the tcm])era- 

 ture is raised still liigher, so that the solid 

 melts and becomes a licpiid, the molecules 

 move in paths so very much greater that 

 there is less common interference. Last- 

 ly, when the licpiid is made to boil, many 

 of the molecules are actually thrown off, 

 and strike against the walls of the en- 

 closing vessel, so violent is their mo\T- 

 ment. The pressure of steam or ol aii\' 

 confined gas, then, must be regarded as a 

 plicnonienon due entirely to millions and 

 niillidiis of blows struck b\' millions and 

 millions of in\isil)le intiniiesimal mole- 

 cules. If a thimbleful of boiling water 

 were magnified to the size of a cathedral 

 the steam within it might seem to a 

 gigantic eye like myriads of bullets shot 

 in all directions. Hecause countless 

 Inillcts strike the walls of this huge 

 thimble not singh', but at once in ver\' 

 rapid succession the effect of stead\' 

 |)ressure is produced. A single finger taj) 



Water was easily pumped for irrigating purposes in 

 Egypt by means of Mr. Shuman's Sun Power Plant 



may not e\en move an open door. A 

 billion simultaneous finger taps will shut 

 it — shut it, moreover, as if it had been 

 pressed by a hand. 



At what temperature the molecules 

 will fiy off from a boiling liquid depends 

 entirely on the pressure to which the 

 licjuid is subjected. The atmosphere 

 weighs down on all earthly things with a 

 pressure that amounts to about fifteen 



pounds to the 

 scpiare inch at 

 thele\elofthc 

 sea. If water 

 is heated in 

 the open air at 

 sea level the 

 flying mole- 

 cules must be 

 able to over- 

 c o m e that 

 pressure; 

 otherwise the 

 water does not 

 boil. The tem- 

 jierature at 

 w h i c h the y 

 can fly o(T at 

 sea level, at 

 which water, 

 in other words 

 can boil, is 

 two hundred 

 and twehe degrees Fahrenheit. On the 

 top of a high mountain where theatmos- 

 l^here jiresses down with less force bei-ause 

 there is less ot it, the molecules will lly 

 off much more readily than at the \c\q\ 

 of the sea, with the result that water 

 will boil much below two hundred and 

 twehe degrees. If it were jjossible to 

 remove the pressure of the atmosphere 

 at sea le\el altogether, water could be 

 made to boil ,u the temperature of an 

 (irdinar\- room without heating it. That 

 feat has actualK' been accomjilished in 

 the laboratory' b>' puni|iing out the air 

 in the water \essel. 



What Mr. Shuman hastlone, therefore, 

 is to remo\e part of the atmosphere's 

 pressure from the hot water so that steam 

 may be gcnera1i'<l. That steam he sup- 

 plies to an enginr w liirh he has designed 

 for the express purjjose of utilizing steam 

 at low pressure, .'\fter doing its work 

 the steam is condensed into water and is 

 ])asse(l back to thegreenhouse-like healer. 



