. Farm implements, and the principles of their construction and use; an elementary and familiar treatise on mechanics, and on natural philosophy generally, as applied to the ordinary practices of agriculture ... 234 PNEUMATICS. the current produced ; or, the oppressive heat of half-story bedrooms may he similarly avoided, by creatinga current of air between the roof and the plastering(Fig. 198). Two modes may be adopted, as repre-sented on each side of the figure. Fig. Mode of Ventilating half-story Bed-rooms. PART IV. HEAT. CHAPTER I. CONDUCTION OF I. CONDUCTING POWER OF BO
. Farm implements, and the principles of their construction and use; an elementary and familiar treatise on mechanics, and on natural philosophy generally, as applied to the ordinary practices of agriculture ... 234 PNEUMATICS. the current produced ; or, the oppressive heat of half-story bedrooms may he similarly avoided, by creatinga current of air between the roof and the plastering(Fig. 198). Two modes may be adopted, as repre-sented on each side of the figure. Fig. Mode of Ventilating half-story Bed-rooms. PART IV. HEAT. CHAPTER I. CONDUCTION OF I. CONDUCTING POWER OF BODIES. When any substance or body has become heated, itloses its heat in two different ways, by conduction andby radiation. When conducted, heat passes off slow-ly or gradually through bodies, as when a pin is heldby the hand in a candle, the heat advancing from oneend to the other till it burns the fingers; or, when aniron poker is thrust into the fire, the heat graduallypasses through it till the whole becomes hot. Ironand brass are, therefore, said to be good conductors ofheat. The end of a pipe-stem may, however, be heatedto redness, and a wooden rod may be set on fire, with-out even warming the other extremity, because theheat is very slowly conducted through them. Woodand burned clay are, therefore, poor conductors. The comparative conducting power of different sub-stances may be shown by placing short rods of eachwith one of their ends in a vessel of hot sand,
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