PRIME-MO VERS. 361 



to describe one of which, about thirty years since, was employed upon 

 Herne Bay Pier ; in fact, this exhibition in the midst of which we are 

 assembled, gives but little encouragement to pursue the subject of 

 prime-movers worked by wind, as I have not as yet come across in 

 the catalogue a reference to any apparatus illustrative of this branch 

 of mechanics. 



It is to be regretted that the use of this kind of prime-mover, the 

 Windmill, is on the decline. It is a power that costs nothing ; the 

 machinery can be erected in almost any situation, and although such 

 power cannot be depended on, being of necessity as uncertain as the 

 wind, it nevertheless might be commonly employed as an auxiliary to 

 steam, diminishing the load upon the engine in exact proportion as the 

 windmill was urged by any wind which might happen to blow. 



I may say to the credit of our American brethren that they 

 employ on their sailing ships a windmill, known by seamen as " The 

 Sailors' Friend," to pump, to work windlasses, and to do all those 

 matters which in a steamship fall to the lot of the donkey-engine and 

 steam winch, unless, as in a recent voyage in which all Englishmen 

 have been so much interested, these duties are imposed upon a baby 

 elephant. 



There is one motor which may be put either into this class or into 

 the next where we consider the application of heat. I allude to the 

 smoke-jack ; but beyond recognising its existence as a prime-mover, 

 and a very early one indeed (it is to be found in Zonca's work pub- 

 lished in 1621), attention need not be bestowed upon it. 



We now come to consider those prime-movers which are worked by 

 heat, and w r e will commence with those which are worked by its 

 immediate and not by its secondary action. 



The direct rays of the sun have for a very long time past been 

 suggested as a means of obtaining motive power. Salomon de Caus, 

 in his work published in 1615, describes a fountain which is caused 

 to operate by the heat of the sun's rays expanding the air in a box and 

 expelling thereby through a delivery valve the water from the lower 

 part of the box. When the sun's rays ceased to impinge upon the box 

 the air cooling, contracted a suction valve opened and admitted more 

 water into the box, to be again displaced on the following day. De 

 Caus also gives a drawing of an apparatus where the effect of the 



