470

Wooden and Granite Boilers.

[Book IV.

and Leopold were the links which connected die labors of Heron , Garay,Porta, Worcester , Moreland, Papin and Savery with those of Watt. Theyopened the way for the introduction of the crank and fly-wheel, which*changed completely the character of the old engines. Like Worcester ’sand Savery’s, Newcomen’s engine required the constant attention of anattendant to open and close the cocks ; but a boy named Potter employedin this Service, stimulated by the love of play, ingeniously added cords tothe levers by which the cocks were turned, and connecting the other endsof the cords to the moving beam, rendered the machine self-acting, and.fhus acquired opportunities of joining his sportive companions unknownto his employers. Iron rods were soon after substituted for the cords byBeighton, and finally Watt and Gainsborough, Hornblöwer, Evans andTrevithick , &c. appeared and made the steam-engine the great primemover of man.

A few subordinate devices relating to steam and steam-engines may herebe noticed. There is in Stuart’s Anecdotes an historical note respectingwooden boilers, in which water is heated by furnaces or flues withinthem. They are traced back to 1663. It may be interesting to somereaders to state, that they were in use in the preceding Century, and thatthe device in all probability dates from even a more remote period. Theyare described in Gesner’s “ Secrets of Phisicke and Philosophie .” In theEnglish translation of 1599, by Baker, to which we have already had re-course, they are twice figured, and thus described : “ A wooden bowle ortubbe of a sufficient compasse and largnesse over: in the middes of whichtubbe erect and set from the bottom unto the edge or brinke of the same,or rather above it, a great copper vessel, in the forme of a hollow pype.Let a parte of the copper pype descende, in such sort and manner, thatthe water be contained betweene the out ward bored wall of the pype and theparte within of the tubbe : But within that parte of the pype which de-scendeth by the bottome of the tubbe, let the fire be put and kindled, for theheating of the water.” Folio 25. The third part of Glauber’s Treatise onPhilosophical Furnaces also relates to wooden boilers, in which liquidswere heated by a copper retort placed in a fire, and whose neck was in-serted in the lower part of the boiler, the liquid circulating through theretort. Eng. Trans, by Dr. French, London , 1652.

We have been informed that an enormous steam boiler for an atmos-pheric engine was in use many years ago at a copper mine near Redruth ,in Cornwall , England, which was composed entirely of large blocks ofgraniie, or “ moor stone,” The water was heated by a furnace, fromwhich iron pipes traversed backward s and forwards in the water.

The old chemists often boiled liquids by the sun’s heat, and a writer inthe London Magazine for 1750 proposed to Substitute the solar rays forcommon fires in heating steam-engine boilers, viz. by collecting the rays ina focus “by means of a common burning glass, or a large concave reflectingmirror of polished metal, or perhaps more conveniently by the newly re-vived method of Arehimedes, which by throwing the focal point to a greaterdistance may be capable of many advantages that the others have not.”He anticipates three objections 1. “The focus will vary with the motionof the sun.” To obviate this he proposes to make the mirror moveableby machinery attached to the engine itself. 2. “ The extreme heat of thefocal point.” If this should be too intense, it may be moderated by en-larging the focus. 3. “ The sun does not constantly shine ”—therefore theengine must stop. This objection, he remarks, is common to wind, tide