NOVUM ORGANUM 385 



reach us), and the heat of the most gentle flame, and even of all ignited 

 substances, nay liquids, or the air itself when unusually heated by fire. 

 For the flame of spirit of wine, though diffused and uncollected, is yet 

 able to set straw, linen, or paper on fire, which animal heat, or that 

 of the sun, will never accomplish without a burning-glass. 



XXI. There are, however, many degrees of strength and weakness 

 in flame and ignited bodies: but no diligent inquiry has been made 

 in this respect, and we must, therefore, pass it hastily over. Of all 

 flames, that of spirits of wine appears to be the most gentle, except, 

 perhaps, the Ignis Fatuus, or the flashes from the perspiration of ani- 

 mals. After this we should be inclined to place the flame of light and 

 porous vegetables, such as straw, reeds, and dried leaves; from which 

 the flame of hair or feathers differs but little. Then, perhaps, comes 

 the flame of wood, particularly that which contains but little rosin or 

 pitch; that of small wood, however (such as is usually tied up in fag- 

 ots), is milder than that of the trunks or roots of trees. This can be 

 easily tried in iron furnaces, where a fire of fagots or- branches of trees 

 is of little service. Next follows the flame of oil, tallow, wax, and the 

 like oily and fat substances, which are not very violent. t But a most 

 powerful heat is found in pitch and rosin, and a still greater in sulphur, 

 camphor, naphtha, saltpetre, and salts (after they have discharged their 

 crude matter), and in their compounds; as in gunpowder, Greek fire 

 (vulgarly called wild fire), and its varieties, which possess such a stub- 

 born heat as scarcely to be extinguished by water. 



XXII. We consider that the flame which results from some imper- 

 fect metals is very strong and active; but on all these points further 

 inquiry should be made. 



XXIII. The flame of vivid lightning appears to exceed all the above, 

 so as sometimes to have melted even wrought iron into drops, which 

 the other flames cannot accomplish. 



XXIV. In ignited bodies there are different degrees of heat, con- 

 cerning which, also, a diligent inquiry has not been made. We con- 

 sider the faintest heat to be that of tinder, touchwood, and dry rope 

 match, such as is used for discharging cannon. Next follows that of 

 ignited charcoal or cinders, and even bricks, and the like; but the most 

 violent is that of ignited metals, as iron, copper, and the like. Further 

 inquiry, however, must be made into this also. 



XXV. Some ignited bodies are found to be much warmer than some 

 flames; for instance, red hot iron is much warmer, and burns more 

 than the flame of spirits of wine. 



XXVI. Some bodies even not ignited, but only heated by the fire, 

 as boiling water, and the air confined in reverberatories, surpass in 

 heat many flames and ignited substances. 



XXVII. Motion increases heat, as is shown in the bellows and the 

 blow-pipe; for the harder metals are not dissolved or melted by steady 

 quiet fire, without the aid of the blow-pipe. 



XXVIII. 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, how- 

 ever, are the same, but the mere motion increases the effect of the 

 heat. 



XXIX. 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. 



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