29t) Translation of Rev's Essai/s. 



having put two pounds six ounces of fine English tin into an 

 iron vessel, and heated it strongly on an open tire for six hours, 

 stirring it continually, without having added any thing, he ob- 

 tained two pounds thirteen ounces of a white calx ; which at 

 first occasioned him great surprise, and the desire to ascertain 

 whence these seven ounces of increase were derived. — Now, to 

 augment the difficulty, I say, that we must not only inquire 

 whence these seven ounces are derived, but, moreover, whence 

 that which has replaced the loss of weight, necessarily arising 

 from the enlargement of volume of the tin, by its conversion 

 into calx, and from the vapours and exhalations that have 

 escaped. To this question, then, resting on the foundations I 

 have laid, I answer, and proudly maintain, " That this increase 

 of weight comes from the air, thickened and made heavy, and 

 in some measure rendered adhesive in the vessel by the violent 

 and long-continued heat of the furnace — which air mixes with 

 the calx (its union being assisted by the continual stirring), and 

 attaches itself to its smallest particles — no otherwise than as 

 water, when sand is thrown into it, makes it heavier by moisten- 

 ing it, and adhering to its smallest grains." I imagine there are 

 many persons who would have been startled (ejfarouchces) at the 

 mere statement of this answer, had I given il in the outset, that 

 will now receive it willingly, being, as I may say, tamed (ap- 

 privoisees) and rendered tractable, by the evident truth of the 

 preceding essays. For doubtless they whose minds were pre- 

 occupied with the opinion that air is absolutely light, would 

 have rushed to the encounter, exclaiming. Why do we not ex- 

 tract heat from cold, white from black, light from darkness, if 

 from air, a thing absolutely light, we can extract so much 

 weight ? And they, who might have given credit to the weight 

 of air, would have been unable to persuade themselves, that it 

 could ever increase the weight of a substance balanced in itself. 

 On this account I have been obliged to shew, that air is pos- 

 sessed of weight ; that it is proved by other investigation than 

 that of the balance ; and that even by that instrument, a portion 

 previously altered and thickened, may make its weight mani- 

 fest. This I have done as briefly as possible, without having 



