106 NOVUM OUGANUM. 



posed, but a more correct one might be derived from con 

 fined air. It is necessary, however, that the air should be 

 enclosed in a vessel of such materials as would not imbue 

 it with heat or cold of themselves, nor easily admit the in 

 fluence of the external atmosphere. The experiment should 

 be made therefore with an earthen jar, covered with folds 

 of leather to protect it from the external air, and the air 

 should be kept three or four days in this vessel well closed. 

 On opening the jar, the degree of heat may be ascertained 

 either by the hand or a graduated glass tube. 



Nineteenth negative to the thirteenth affirmative. 



There is a similar doubt as to whether the warmth of 

 wool, skins, feathers, and the like, is derived from a slight 

 inherent heat, since they are animal excretions, or from 

 their being of a certain fat and oily nature that accords with 

 heat, or merely from the confinement and separation of air 

 which we spoke of in the preceding paragraph. 5 * For all 

 air appears to possess a certain degree of warmth when 

 separated from the external atmosphere. Let an experi 

 ment be made therefore with fibrous substances of linen, 

 and not of wool, feathers, or silk, which are animal excre 

 tions. For it is to be observed that all powders (where air 

 is manifestly enclosed) are less cold than the substances 

 when whole, just as we imagine froth (which contains air) 

 to be less cold than the liquid itself. 



Twentieth negative to the fourteenth affirmative. 



We have here no exactly negative instance, for we are 

 not acquainted with any body tangible or spirituous which 

 does not admit of heat when exposed to the fire. There is 

 however this difference that some admit it more rapidly, as 

 air, oil, and water, others more slowly, as stone and metals.f 

 This, however, belongs to the table of degrees. 



Twenty-first negative to the fifteenth affirmative. 



No negative is here subjoined, except the remark that 

 sparks are not kindled by flint and steel, or any other hard 

 substance, unless some small particles of the stone or metal 

 are struck off, and that the air never forms them by friction 

 as is commonly supposed ; besides, the sparks from the 

 weight of the ignited substance, have a tendency to descend 

 rather than to rise, and when extinguished become a sort 

 of dark ash. 



* This last is found to be the real reason air not being a good conductor, and 

 therefore not allowing the escape of heat. The confined air is disengaged when 

 these substances are placed under an exhausted receiver. 



t This is erroneous. Air in fact is one of the worst, and metals are the best 

 conductors of heat. 



