Twining’s inventions in the United States in 1853 and 1862 of the compression machine, followed by Pictet of France, and a number of improvements elsewhere have bid fair to displace the absorption method. In dispensing with absorption these machines proceed on the now well-established theory that air and many other gases become heated when compressed; that this heat can then be drawn away, and that when the gas is allowed to re-expand it will absorb a large amount of heat from any solid or fluid with which it is brought in contact, and so freeze it. Accordingly such machines are so constructed that by the operation of a piston, or pistons, in a cylinder, and actuated by steam or other motive power, the air or gas is compressed to the desired temperature, the heat led off and the cold vapour conducted through pipes and around chambers where water is placed and where it is frozen. By the best machines from five hundred to one thousand pounds of ice an hour are produced. The art of refrigeration and of modern transportation have brought the fruits of the tropics in great abundance to the doors of the dwellers of the north, and from the shores of the Pacific to the Atlantic and across the Atlantic to Europe. A train of refrigerator cars in California laden with delicious assorted fruits, and provided with fan blowers driven by the car axles to force the air through ice chambers, from whence it is distributed by perforated pipes through the fruit chambers, and wherein the temperature is maintained at about 40° Fah., can be landed in New York four days after starting on its journey of 3,000 miles, with the fruits in perfect condition. But the public is still excited and wondering over the new king of refrigeration--_liquid air_. As has been stated, the compression of air to produce cold is a modern discovery applied to practical uses, and prominent among the inventors and discoverers in this line have been Prof. Dewar and Charles E. Tripler. Air may be compressed and heat generated in the process withdrawn until the temperature of the air is reduced to 312° below zero, at which point the air is visible and to a certain extent assumes a peculiar material form, in which form it can be confined in suitable vessels and used as a refrigerant and as a motor of great power when permitted to re-expand. It is said that it was not so long ago when Prof. Dewar produced the first ounce of liquid air at a cost of $3,000, but that now Mr. Tripler claims that he can produce it by his apparatus for five cents a gallon.