Third, _The lack of attention to gain or loss of weight_. It was in past times not recognised that nothing could be created and nothing destroyed. In popular language, a candle is destroyed when it is burned, nothing visible being produced from it. The products, we now know, are gaseous and invisible, and possessed of greater weight than the unburnt candle; but for want of careful experiment, it was formerly concluded that the candle, when burnt, was annihilated. The formation of a cloud in a cloudless sky; the growth of vegetables in earth, from which, apparently, they did not derive their substance; and the reputed growth of metalliferous lodes in mines--these were all adduced as proofs of the creative power of Nature. With such ideas, therefore, the necessity of controlling the gain or loss of material during experiment, by determining gain or loss of weight, did not appear imperative; and hence but few quantitative experiments were made, and little importance was attached to these few. It had, for example, long been noticed that certain metals gained weight when burned and converted into a “calx,” or, as we should now say, a metallic oxide, but such gain in weight was not regarded as of any consequence. When considered in relation to the supposed loss of “phlogiston” suffered by a metal on being converted into a calx, it was explained by the hypothesis that phlogiston possessed “levity”--the antithesis of gravity--and that the calx weighed more than the metal, owing to its having lost a principle which was repelled instead of being attracted by the earth. Among the most remarkable early attempts to elucidate the true nature of air, we meet with one by the Hon. Robert Boyle, who published about the middle of the seventeenth century his _Memoirs for a General History of the Air_. Boyle was one of the most distinguished scientific men of his own, or indeed of any, age, and in his spirit of calm philosophical inquiry he was far in advance of his contemporaries. He was born in the early part of the year 1626, in Ireland, whither his father, Richard Boyle, had emigrated at the age of twenty-two. Boyle’s mother, daughter of Sir Geoffrey Fenton, principal Secretary of State for Ireland, died while he was still a child. Yet she must have lived in the recollection of her son Robert, for he wrote: “To be such parents’ son, and not their eldest, was a happiness that our Philarethes (himself) would mention with great expressions of gratitude; his birth so suiting his inclinations and designs, that had he been permitted an election, his choice would scarce have altered God’s discernment.”