In 1845 the late Professor Faraday delivered a lecture on the solidification of gases at the Royal Institution, and demonstrated his facts by experiments as interesting as they were successful. Under his skilful manipulation a tube filled with olefiant gas, quite invisible, was seen to become partially filled with a colourless liquid, which was the gas in a condensed form. Two conditions were shewn to be essential to the result‒extreme pressure, and extreme cold. The pressure was obtained by strong mechanical appliances, and the cold by means of solidified carbonic acid, which looked like lumps of snow. In this way the lecturer made clear to a general audience the process by which a number of gases had been brought into a liquid or solid form; and he stated that he had ‘hoped to make oxygen the subject of the evening’s experiment, but from some undetected cause it had baffled his attempts at solidification.’ Nevertheless, he looked forward to the time when not only oxygen, but azote and hydrogen would be solidified, and he agreed with Dumas, of the Institute of France, that hydrogen would shew itself in the form of a metal. Faraday’s anticipation is now realised in one particular, for oxygen has been liquefied. This achievement is due to the enlightened and persevering efforts of Mr Pictet, an able physicist of Geneva. Working with apparatus capable of resisting a pressure of eight hundred atmospheres, and a temperature sixty-five degrees below zero (centigrade), he succeeded in converting oxygen (invisible) into a visible liquid which spouted from the tube in which it had been inclosed for experiment. It is a feat which involves important consequences for science. It is a further confirmation of the mechanical theory of heat, according to which all gases are vapours capable of passing through the three states‒solid, liquid, and gaseous. Geneva winds up the year with a fine scientific triumph. Will Albemarle Street supplement it by liquefying or solidifying azote and hydrogen? Just as these lines are going to press we hear a rumour that it has been done by a Frenchman at Paris.