“To produce air by fermentation in sealed glasses. “To separate air from liquors by boiling. “To separate air from liquors by the air-pump. “To produce air by corrosion, especially with spirit of vinegar. “To separate air by animal and sulphureous dissolvants. “To obtain air in an exhausted receiver by burning-glasses and red-hot irons. “To produce air out of gunpowder and other nitrous bodies. “2. To examine the produced aerial substances by their preserving or reviving animals, flame, fire, the light of rotten wood, and of fish. “To examine it by its elasticity, and the duration thereof. “To do the same by its weight, and its elevating the fumes of liquors.” We shall all agree that if Boyle had successfully carried out such experiments, our knowledge of the true nature of air would have come quite a century before it did. Some of these experiments were indeed made by John Mayow, his contemporary, whose work and speculations we shall now proceed to consider. John Mayow was born in the parish of St. Dunstan, London, in 1645. His family was originally Cornish, having come from Bree, in Cornwall. He entered Wadham College, Oxford, at the early age of sixteen, and was shortly afterwards made a probationer-fellow of All Souls’ College. After the usual three years of study, he took his degree in Law; but not being attracted by the legal profession, he turned his attention to medicine, and became a medical practitioner at Bath, where he lived during the fashionable season. When not more than twenty-three years of age, he wrote two essays on Respiration, ascribing the inflation of the lungs to the action of the intercostal muscles. These “Tractatus duo” were published in 1668. Some years later he produced the treatise on which his fame rests; it is entitled “Tractatus quinque medico-physici, quorum primus agit de sal-nitro et spiritu nitro-aëreo; secundus, de respiratione; tertius, de respiratione foetus in utero et ovo; quartus, de motu musculari, et spiritibus animalibus; ultimus, de rhachitide; studio Joh. Mayow, LL.D. & Medici, nec non Coll. Omn. Anim. in Univ. Oxon. Socii. Oxonii e Theatro Sheldoniano, An. Dom. MDCLXXIV.” The work was dedicated to Sir Henry Coventry. It was inserted in an abridged form in the _Philosophical Transactions_ of the Royal Society, some time after its publication, but received only scant recognition, for the fame of Newton and Boyle overshadowed the labours of less well-known investigators. And Mayow did not live to press his discoveries on the attention of his contemporaries, for he died in 1679, five years after the publication of his tracts, in his thirty-fourth year. Little is known of Mayow’s domestic life, save that he married shortly before his death. His scientific work proves that if he had been granted the usual span of life, his extraordinary genius would have furthered the knowledge of the true explanation