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Bas MARINE of the cylinder and cuts the cylinder in two, except for the bars across the opening. When the piston is at the end of its stroke, this port is entirely open, but as the piston moves on it gradual- ly closes it, doing so completely somewhat before half stroke. As is seen at once, the pump is simplicity itself, It is not an experiment in these boats, as one has been tested at various speeds up to 1,000 revolutions per minute with excellent results. To get this last speed, the screw of the launch on which the test was made was removed, and as the condenser was of the keel type, there was naturally very poor circulation of the cooling water, being merely that due to the current in the river. Yet, even under these disadvantageous circumstances, a vacuum was obtained of 20 inches. 'This is one of the most remarkable feats in connection with air pumps on record. It will be readily understood that the use of a pump driven from the main engine and at this high speed saves a great deal of weight. While the boat is in motion, the cooling water will be cir- culated through the condenser tubes by means of scoops over the injection. and outboard delivery openings, as is the common practice with all torpedo boats, while an auxiliary circulating pump of the centrifugal type is fitted with a capacity sufficient to just condense all the steam the boiler will make when the boat is stopped. | The boiler of each boat will be of the coil or tubulous type and it is probable that different makes will be used in the differ- ent-boats so as to get experience with all those of good makers. The navy department is thoroughly in earnest in the matter of the introduction of coil boilers as soon as their durability has been thoroughly established, and the building of these boats gives an excellent opportunity tor a comparative test. 'The forced draft will be on the closed fire room system and it is prob- able that quite a high air pressure will be used, as the great elas- ticity and thinness of coil boilers enables them to stand any de- gree of forcing without injury. An interesting feature, as shown on the drawing of the engines, which is given on page 6, is the shafting. It hardly amounts to more than a pipe, as the thickness is only three- eighths of an inch. This was done, of course, to secure light- ness, and comes about because it was necessary to make the ex- ternal diameter as much as it is to secure bearing surface for the journals. As this would give a strength considerably in excess of the actual requirements if solid, it has been possible to make a relatively large hole. In large shafting the internal diameter REVIEW. rarely exceeds 50 per cent. of the external, while in this case it is more than 75 per cent. The speed of the Maine's boats is expected to be 18 knots and that of the boats of the Texas 17 knots. The hull and machinery of the former are building at the New York navy yard, while those of the latter are building at the Norfolk yard. i ee ee Seis etait COT peas anh ole ool ye eo j Wh Sy uae a.