It has not yet been done; but the following telegrams, received on the 9th and 16th of April, 1883, from Cracow, by the Paris Academy of Sciences, show that chemists have come very near doing it. “Oxygen completely liquefied; the liquid colorless like carbonic acid.” “Nitrogen liquefied by explosion; liquid colorless.” Thus the two elements that make up atmospheric air have actually been liquefied, the successful operator being a Pole, Wroblewski, who had worked in the laboratory of the French chemist, Cailletet, learnt his processes, copied his apparatus, and then, while Cailletet, who owns a great iron-foundry down in Burgundy, was looking after his furnaces, went off to Poland, and quietly finished what his master had for years been trying after. Hence heart-burnings, of which more anon, when we have followed the chase up to the point where Cailletet took it up. I use this hunting metaphor, for the liquefaction of gases has been for modern chemists a continual chase, as exciting as the search for the philosopher’s stone was to the old alchemists. Less than two hundred and fifty years ago, no one knew anything about gas of any kind. Pascal was among the first who guessed that air was “matter” like other things, and therefore pressed on the earth’s surface with a weight proportioned to its height. Torricelli had made a similar guess two years before, in 1645. But Pascal proved that these guesses were true by carrying a barometer to the top of the Puy de Dôme near Clermont. Three years after, Otto von Guerecke invented the air-pump, and showed at Magdeburg his grand experiment—eight horses pulling each way, unable to detach the two hemispheres of a big globe out of which the air had been pumped. Then Mariotte in France, and Boyle in England, formulated the “Law,” which the French call Mariotte’s, the English Boyle’s, that gases are compressible, and that their bulk diminishes in proportion to the pressure. But electricity with its wonders threw pneumatics into the background; and, till Faraday, nothing was done in the way of verifying Boyle’s Law except by Van Marum, a Haarlem chemist, who, happening to try whether the Law applied to gaseous ammonia, was astonished to find that under a pressure of six atmospheres that gas was suddenly changed into a colorless liquid. On Van Marum’s experiment Lavoisier based his famous generalisation that all bodies will take any of the three forms, solid, fluid, gaseous, according to the temperature to which they are subjected—i.e., that the densest rock is only a solidified vapor, and the lightest gas only a vaporised solid. Nothing came of it, however, till that wonderful bookbinder’s apprentice, Faraday, happened to read Mrs. Marcet’s Conversations while he was stitching it for binding, and thereby had his mind opened; and, managing to hear some of Sir H. Davy’s lectures, wrote such a good digest of them, accompanied by such a touching letter—”Do free me from a trade that I hate, and let