Translation of Key's Essays. 295 



by the sole aid of nature, very expert in this operation — not that 

 art is unable to increase or diminish the weight of things, di- 

 lating or contracting them. Hammer a piece of cold iron for a 

 considerable time ; you will unite its parts and diminish its bulk, 

 and then it will appear heavier when put into the balance. Like- 

 wise, if you put a ball of feathers, closely tied up, into the 

 scale, it will weigh more than when the feathers are left at their 

 full size. From this I infer, what has been already cursorily 

 touched on, that the balance is so fallacious, that it never indi- 

 cates the true weight of substances, except when two portions 

 of the same substance and figure, as two leaden bullets, are 

 counterpoised against each other. But two ingots, one for in- 

 stance of gold, and the other of iron, which appear by the 

 balance to be equal, are nevertheless not so — for the iron is as 

 much heavier than the gold, according to reason, as the air 

 which it displaces is heavier than that displaced by the gold, 

 which difference I could shew exactly in every thing we weigh, 

 and could reduce the whole to its just weight, if I had made the 

 trial I have suggested above in the 7th essay. 



Essay XVI. 



Formal answer to the question, Why Tin and Lead increase in 

 weight when they are calcined* ? 



I have now made the preparation ; laid as it were the founda- 

 tions of my answer to the Sieur Burn's demand ; namely, that 



* Note hy M. Gobet. 



John Baptist Porta, a Neapolitan gentlemaD, author of several works 

 on Natural History and Agriculture, has recorded the same fact. 



" Plumbum pondcrosius reddere, docet Galenus. Nam comprobans 

 |>luiubuni particeps esse aerese substantite, hoc affert cxperimentum. Om- 

 nium quse novimus, uuicum plumbum, tum mole ipsA., tum pondere an- 

 gctur, si coiidatur iu aedibus subterraueis, ai^rem hal>eutibus turbidum, ila 

 ut quscunique illic ponaiitur, cclcritcr situm colligant. Tum ctiam plum- 

 bea statuarnm vincula, (|uibus earum pedes aunectuutiir, sacpe numero 

 crevissc visum est, et quxdam adeo intumuisse, ut ex lapidibns dcpcnde- 

 rent oryitalli, modo verructe." (Lib. v. cap. 11.) — Magia Naturalis, 

 libriviginti — Hanovioe, 1619. 



Bacon iiay» the same, — (Sylva Sylvarum.) 



