142 NOVUM ORGANUM 



and the blowpipe; for the harder metals are not dissolved 

 or melted by steady quiet fire, without the aid of the blow 

 pipe. 



28. Let an experiment be made with burning-glasses; in 

 which respect I have observed, that if a glass be placed at 

 the distance of ten inches, for instance, from the combustible 

 object, it does not kindle or burn it so readily, as if the glass 

 be placed at the distance of five inches (for instance), and be 

 then gradually and slowly withdrawn to the distance of ten 

 inches. The cone and focus of the rays, however, are the 

 same, but the mere motion increases the effect of the heat. 



29. Conflagrations, which take place with a high wind, 

 are thought to make greater way against than with the wind, 

 because when the wind slackens, the flame recoils more 

 rapidly than it advances -when the wind is favorable. 



30. Flame docs not burst out or arise unless it have 

 some hollow space to move and exert itself in, except in the 

 exploding flame of gunpowder, and the like, where the com 

 pression and confinement of the flame increase its fury. 



31. The anvil becomes so hot by the hammer, that if it 

 Were a thin plate it might probably grow red, like ignited 

 iron by repeated strokes. Let the experiment be tried. 



32. But in ignited bodies that are porous, so as to leave 

 room for the fire to move itself, if its motion be prevented 

 by strong compression, the fire is immediately extinguished; 

 thus it is with tinder, or the burning snuff of a candle or 

 lamp, or even hot charcoal or cinders; for when they are 

 squeezed by snuil ers, or the foot, and the like, the effect of 

 the fire instantly ceases. 



of vivid lightning mentioned in No. 23 contains so much vigor, its velocity 

 being greater than that arising from other heat. Ed. 



