470 KOVUM ORGANUM. [bOOK 11. 



as straw, reeds, and dried leaves ; from which the flame of hair 

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

 wood, particularly that which contains but little rosin or pitch; 

 tliat of small wood, however (such as is usually tied up in 

 fatjots), is milder than tliat of the trunks or roots of trees. 

 Tliis can be easily tried in iron furnaces, where a fire of fagots 

 or brandies 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. But a most powerful heat is found in 

 pitch and rosin, and a still greater in sulphur, camphire, naphtha, 

 saltpetre, and salts (after they have discliarged their crude 

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

 (vulgarly called wild fire), and its varieties, which possess 

 such a stubborn heat as scarcely to be extinguished by water. 



22. We consider that the flame which results from some im- 

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

 further inquiry should be made. 



23. 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. 



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

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

 consider 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. 



25. 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. 



26. 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. 



27. 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. 



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

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

 distance often inches, for instance, from the combustible object, 

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



* The coiTect measure of the activity of flame may be obtained by 

 multiplying its natural force into the square of its velocity. On this 

 ilccount the flame of vivid lightning mentioned in No. 23, containa 

 BO much vigour, its velocity being greater than th»> -jrising from other 

 beat. Ed. 



