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30 In operation the leading edge and ad- vancing surface of each blade when ro- tating enters new water to advance the propeller and ship to which it is attached, but because of the absence of this foci and of eddies usually produced by other curved surfaces having foci there is no interference or tendency on the part of one wave (of water) to interfere with another wave. Hence the resistance in front of the blade is reduced to a com- paratively small amount while the pres- THE Marine REVIEW sure behind the propeller is not mate- rially reduced. - ; The blades are preferably so located about the hub that their bases will be at an angle of between 20° and 30° with its axis. As each blade spreads itself preferably from the hub to its extremity the leading edge or entering corners of : the blade is in a plane nearly parallel with the axis of rotation so that it cuts the new water with practically no resistance. This result is, in the opinion of the inventor, due to the peculiar prop- erty which the convex surface, in this case also conchoidal, has of behaving jp the same manner as the concave, anq conchoidal surface, as regards interfer. ence. The inventor, Edmund D. Spear, of Boston, Mass., believes the propeller would be equally efficient in air, and though aware that propellers have been constructed, the blades of which haye cross sections representing reversed of inflected curves, does not claim a pro- peller having blades with merely that construction. The Progress of River Improvements in the Vicin- By the final completion of a number of- works long under construction, the artificial navigation of rivers at Pittsburg has been extended farther during the past year than in any pre- vious season in the history of their improvement in this locality. The Pittsburg Engineer district, at pres- ent in charge of Major H. C. New- comer, corps of engineers, United States army, comprises the Allegheny and Monongahela rivers, and the Ohio river from its. source to the Ohio- Pennsylvania state line, and their trib- utaries. Belonging to the govern- ment for the purposes of navigation there are now completed and in op- eration on the rivers in this district 24 dams with 28 locks, the lower four locks on the Monongahela river be- ing double. Of the dams 15. are lo- cated on the Monongahela, three on the Allegheny and six on the Ohio river. The Monongahela dams are all of the fixed or stationary type, al- though dams 2 and 3, recently rebuilt, have adjustable crests 3 ft. high of Chittenden drums. These are built of steel and are capable under certain water conditions of being raised by hydraulic or pneumatic forces over full length of dam in a few seconds. The Allegheny river has two fixed' and one movable dams, and the six Ohio river dams are all movable,-- of the Chanoine type with bear-trap regulating weirs. Within a year all of the locks and dams under construction or recon- struction in this district, except No. 5 on the Monongahela river, at *United States assistant engineer in charge of movable dams in the Pittsburg engineer dis- trict, ity of Pittsburg. BY J. W. ARRAS.* Brownsville, have been completed and placed in commission. These re- cent additions to the local navigation comprise dams 3, 4 and 5, Ohio river, extending slackwater man's, near the foot of Neville island, about 16 miles to Freedom, Pa., and Nos. 2 and 3, Allegheny river, adding approximately 18 miles to its naviga- tion above Sharpsburg. New No, 3, Monongahela river, at Elizabeth, also was completed and the old structure, about a mile above, largely removed. By means of these extensions there has been provided a continuous nav- igation, varying from 6 to 9 ft. depth at Jowér. sills- of locks from. Fair- mont, W. Va., on the Monongahela river, to Merrill, Pa., three miles be- low Beaver,,on the Ohio, a distance of 160 miles, and extending up the Allegheny river about 25 miles to Natrona. This accomplishment of 185 miles of artificial waterway has covered a period of about 70 years, although much of the greater part of it has been acquired or effected in the past 12 years. Early in 1840 the first two locks and dams were putin operation on the Monongahela river, No. 1 within 114 miles of its mouth, and No. 2 at Port Perry, above Tuttle creek. These were followed in 1844 by Dams 3 and 4, extending slack- water to Brownsville, a distance of 57 miles above Pittsburg. These im- provements were established by the Monongahela' Navigation Co, °a cor- poration of the state of Pennsylvania, which subsequently also added locks and dams 5, 6 and 7, extending slack- water to the West Virginia state line, approximately 93 miles above the from Merri-: mouth of the river. In the meantime the United States had undertaken the construction of dams 8 and 9, con- tinuing the canalization of the stream to Morgantown, W. Va., which ser- vice was finally completed in 1889, Then for a season improvements on the Monongahela river ceased, and it was not until 1896 that further appro- priations were made for the con- struction of additional works. On that occasion the government under- took as a single project the extension of slackwater from Morgantown to Fairmont, W. Va., comprising six locks and dams. These were complet- ed and placed in operation in 1903, yielding 130 miles of continuous, per- manent navigable water of a least, depth of from 6 to 8 ft. in the vari- ous pools on that stream. In 197 after prolonged agitation all along the rivers from Pittsburg to the Gulf of the question of. freeing the. lower Monongahela of tolls, the United States purchased the Navigation com- pany's plant, comprising the seven lowermost docks and dams, at a cost of $3,761,615.46. Enjoying for the first time entire freedom from toll charges the commerce of. this river, under the influence of the prosperous times which immediately followed in- creased very rapidly, creating a de- mand for extended lockage facilities, particularly in the five lowermost pools. About the same time also the continuous hard usage of the already badly dilapidated navigation company structures began to affect their sta- bility materially, so much indeed that it became necessary immediately t0 make provision for the reconstruction at least of those in worst condition,