BOOK II.] APIIOHTSM& 457 



But natural and experimental history is so varied and diffuse, 

 that it confounds and distracts the understanding unless it be 

 fixed and exhibited in due order. We must, therefore, form 

 tables and co-ordinations of instances, upon such a plan, and in 

 such order, that the understanding may be enabled to act upon 

 them. 



Even when this is done, the understanding, left to itself and 

 to its own operation, is incompetent and unlit to construct its 

 axioms without direction and support. Our third ministration, 

 therefore, must be true and legitimate induction, the very key of 

 interpretation. &quot;We must begin, however, at the end, and go 

 back again to the others. 



XI. The investigation of forms proceeds thus : a nature being 

 given, we must first present to the understanding all the known 

 instances which agree in the same nature, although the subject 

 matter be considerably diversified. And this collection must be 

 made as a mere history, and without any premature reflection, or 

 too great degree of refinement. For instance ; take the investi 

 gation, of the form of heat. 



Instances agreeing in the Form oj Heat. 



1. The rays of the sun, particularly in summer, and at noon. 



2. The same reflected and condensed, as between mountains, 

 or along walls, and particularly in burning mirrors. 



3. Ignited meteors. 



4. Burning lightning. 



5. Eruptions of flames from the cavities of mountains, &c. 



6. Flame of every kind. 



7. Ignited solids. 



8. Natural warm baths. 



9. Warm or heated liquids. 



10. Warm vapours and smoke ; and the air itself, which 

 admits a most powerful and violent heat if confined, as in rever 

 berating furnaces. 



11. Damp hot weather, arising from the constitution of the 

 air, without any reference to the time of the year. 



12. Confined and subterraneous air in some caverns, parti 

 cularly in winter. 



13. All shaggy substances, as wool, the skins of animals, anl 

 tho plumage of birds, contain some heat. 



14. All bodies, both solid and liquid, dense and rare (as the 

 air itself), placed near fire for any time. 



15. Sparks arising from the violent percussion of flint and 

 steel. 



10. All bodies rubbed violently, as stone, wood, cloth, &c., sc 

 that rudders, and axles of wheels, sometimes catch fire, and the 

 West Indians obtain fire by attrition. 



17 Green and moist vegetable matter confined aJ rubbed 



