early days would be clogged by leaves or anchor ice in spite of the best of screens; until the head-gates were closed, the shop was stopped, 500 men prevented from working and the wheel was cleaned out. Such wheels cannot be sold now. In order to put a new step into the wheel, planks must be dropped into the tailrace, or back-gates closed, the pit must be pumped out by steam power or hand until the step could be reached. Now the wheel is placed about ten feet above the tail-water, where every part is accessible. The old gears are gone and the power is carried by a straight belt from the shaft of the water-wheel to the work. Everything moves faster than fifty years ago. Shafting, machinery, railroad cars, steam engines, all have rapid speed. The American type of water wheel is capable of a high speed, and thereby well fitted to the times.

A history of American water-wheels would not be complete without mentioning the American type of jet wheels. These have been developed here more than in foreign countries. Their peculiarity is that the water is discharged into them through a nozzle like that of the hose of a hydrant. They are better adapted to high falls than the pressure or ordinary turbine because they can be made larger in diameter, and also because, when of the same diameter and operating under the same fall, they travel at only one-half the speed of the ordinary pressure turbine. Under a fall of 100 feet the average small pressure turbine will make 1,500 revolutions per minute, while the jet wheel, like the above cut, will make only 300. Hence the small pressure turbine soon wears out and loses its efficiency, while the jet wheel retains it. When both are new and in good order the jet wheel has a higher efficiency than the small turbine. The latter would rarely hold an efficiency of 70 per cent in the testing flume. It would be less economical of water than the overshot, although the turbine of medium or large size is usually more economical of water. The jet wheel of proper construction is capable of a high efficiency. Many of them have given an efficiency of more than 85 per cent; several of them have given more than 90 per cent. But the experience of the writer in testing them is that they do not maintain that high efficiency. Different sizes show different results and do not repeat as well as the pressure turbine. A rusty nozzle, buckets with blunt cutting edges, setting the nozzle at a wrong angle, and other errors, will easily reduce their efficiency 10 per cent. But, even then, they are more economical than the small turbine.

The principle of these wheels is different from that of the pressure turbine. The water runs through the nozzle in theory with the velocity due to the entire fall, and in practice with about 98 per cent of that velocity. The wheel should run by theory with one-half the velocity due to the fall, but in practice it gives its best percentage of efficiency when running about 42 per cent of the velocity due to the fall. The water should be thrown back

by the wheel with a velocity equal to the difference between the two velocities, which in theory is one-half the velocity due to the fall. Then, if the wheel moves forward with one-half the velocity due to the fall and the water is thrown backwards from the wheel with one-half the velocity due to the fall, the two will equalize each other and the absolute velocity of the water will be nothing, and all the force of the water will have been used in giving power to the wheel. The water enters the wheel without pressure and the reaction is obtained from momentum alone.

In the ordinary type of turbines which have been previously described, half of the fall is used in carrying the water through the stationary chutes or guides and half in carrying it through the wheel. The wheel travels with the velocity due to half the fall. The water enters the wheel at the same velocity without shock or disturbance. Both are traveling at the same velocity. In the runner the water operates under the pressure of half of the fall. The pressure of the last half of the fall drives the wheel by its reaction. The velocity due to half the fall is seven-tenths that due to the whole fall and 40 per cent. more than one-half that due to the entire fall. In practice the periphery of the pressure turbine travels with about 78 per cent. of the velocity due to the fall, and the jet wheel travels with 42 per cent. the velocity due to the fall. Hence the pressure turbine has nearly twice the velocity of the jet wheel of the same diameter operating under the same fall. For heads of over fifty feet, where less than 100 horse-power is required, the jet wheel runs slower and is better than the pressure turbine. The pressure turbine must be fed regularly on its whole perimeter or it will lose its efficiency, since the pressure of the water in the bucket is the source of the entire power. But the water is not acting under pressure in the jet wheel and it can be fed on the entire perimeter or on any part of The jet wheel must always run in air and no draft tube can be used with it.

it.

The credit for the success of this American type of the jet wheel belongs to the Pelton Water-wheel Co. of San Francisco, Cal. Mr. Pelton saw the great need of a water-wheel suitable to the high falls and limited quantity of water of many locations on the Pacific coast. This was specially true of smelting and mining plants. The amount of power required was small. The little turbines which had previously been used ran too fast; their bearings would heat and wear out. They were not durable and they clogged easily. Pelton was a mechanic of limited education but a genius. He knew nothing of brake and weir tests when he originated his wheel, but he knew how to build a water-wheel which satisfied the wants of his customers. He was first engaged as a mill-wright to design some water-wheels for high falls. They were found to be superior to any others for this work. Capitalists became interested and helped him. The enterprise was well managed and large numbers were sold and gave good

satisfaction. Wheels of the same character are now built by other firms.

DISCUSSION.

Mr. Feldman: I would like to make a few remarks in regard to the Fourneyron type of turbine. It was introduced in this country by Mr. Boydon, of Massachusetts, who made some improvements in its design. The wheel is of the radial outwardflow type.

Being a reaction turbine it works efficiently only when the buckets are full of water. During the regulation of its speed, the supply of water is being decreased, then the buckets would not be full of water and the efficiency of the wheel thus diminished. To overcome this difficulty the turbines are built several stories high. The turbines used by the Niagara Falls Power Co. are twin wheels, three stories high, of the Fourneyron type, designed by two Swiss engineers.

President Noble: Can you give us some idea of the tests by which that wheel was supposed to be proved superior?

Mr. Feldman: The Niagara Falls turbines are developing.5000 effective horse power each.

Tests have shown that their efficiency is about 7.5 per cent.

XXX.

"MECHANICAL PLANTS OF LARGE BUILDINGS.

By DANKMAR ADLER, Mem. W. S. E.

Read March 16, 1898.

It is only within a very few years that the general public has begun to realize the extent and the importance of the machinery plants, without which our large business buildings of every type could not be occupied or used. Business men could not bring themselves to believe that the engineering equipment necessary for promoting the comfort and health of the permanent and transient occupants of a large business building could equal, much less exceed, in importance, magnitude or difficulty the mechanical plant of an ordinary factory. In those days the trusted engineering expert was for each business man interested in a steam plant his own "engineer," so called because he periodically opened and closed the throttle of an engine, which he oiled and cleaned and looked after generally, when not occupied with the shoveling of coal or the removal of clinker and ash. But as each of these so-called "engineers" rarely had more than his own observations and experiences to fall back upon, and as the collated records of the world's work and the comparisons, researches and conclusions based thereon were to him a sealed book, his mental horrizon was painfully narrow. If such men were enterprising and progressive, they were apt to favor the use of expedients before tried by others and found impracticable, or if, as was more generally the case, they were obstinately and honestly conservative, they opposed innovations upon the practice known to themselves with a doggedness of purpose which generally carried conviction to the minds of their employer. As a consequence the heat and power plants of the business buildings erected in the sixties, seventies and early eighties, were exceedingly crude and wasteful. Sixty pounds was the maximum steam pressure used. It was always safe to assume that either boiler or stack, or both, were too small. Exhaust steam was always blown into the air, barrels of water of condensation were run into sewers. Pipes were irregu larly, ignorantly and arbitrarily proportioned, and there was scarcely a time during the period of operation of steam-heating apparatus when the ear was not assailed by sounds reminding an old soldier of the transition from lively skirmish to actual battle. It was a blessed era for contractors. Their specifications and their planning became the final refuge of the coal shoveling engineer. The contractor was bound to have his own way, for he claimed that otherwise he could not be held responsible for results. And then after the contractor had had full swing and, as