The diagrams are reduced from the originals, taken from the compression cylinder when running at the speed of 125 revolutions per minute, and also from the expansion cylinder, the first when the cooling water was entering the coolers at 86 deg. Fah., and the latter when this temperature was reduced to 65 deg. Fah. In all cases the compressed air is cooled down to within from 3 deg. to 5 deg. of the initial temperature of the cooling water, thus showing the great efficiency of the cooling apparatus. The machine has been run experimentally at Dartford, under conditions perhaps more trying than can possibly occur, even in the tropics, the air entering the compression cylinder being artificially heated up to 85 deg. and being supersaturated at that temperature by a jet of steam laid on for the purpose. In this case no more snow was formed than when dealing with aircontaining a very much less proportion of moisture. The vapor was condensed previous to final expansion and abstracted as water in the drying apparatus. The machine was exhibited at work in connection with a cold chamber which was kept at a temperature of about 10 deg. Fah., besides which several hundredweight of ice were made in the few days during which the experiments lasted. This machine is in all respects an improvement on the machine which we have already illustrated. In that machine Messrs. Hall were trammeled by being compelled to work to the plans of others. In the present case the machine has been designed by Mr. Lightfoot, and appears to leave little to be desired. It is a new thing that a cold air machine may be run at any speed from 32 to 120 revolutions per minute. In its action it is perfectly steady, and the cold air chamber is kept entirely clear of snow. The dimensions of the machine are also eminently favorable to its use on board ship.-_The Engineer_. [Illustration: DRY AIR REFRIGERATING MACHINE] * * * * * THOMAS'S IMPROVED STEAM WHEEL. The rotary or steam wheel, the invention of J.E. Thomas, of Carlinville, Ill., shown in the annexed figure, consists of a wheel with an iron rim inclosed within a casing or jacket from which nothing protrudes except the axle which carries the driving pulley, and the grooved distributing disk. Within this jacket, which need not necessarily be steam-tight, there is a movable piece, K, which, pressing against the rim, renders steam-tight the channel in which the pistons move when driven by the steam. At the extremities of this channel there are plates which are kept pressed against the wheel by means of spiral springs, thus rendering the channel perfectly tight.