70 TECHNOLOGY. 
upon the top of the wheel, over-shot wheels. In breast wheels the water strikes 
the wheel upon a level with its axis. 
Formerly water-wheels were built of wood; more recently, however, cast- 
iron has been used, not only for the disks which support the buckets, but 
also for the buckets themselves, the whole being put together by serews 
upon the spot where it is to be put up. 
An important part of the water-wheel is the bucket, an idea of the form 
and position of which may be gathered from pl. 15, fig.1. It will readily 
be seen that one desideratum with over-shot wheels is to keep the buckets 
filled with water until they reach the lowest point of their revolution ; this 
in practice it is impossible absolutely to accomplish. At first, the buckets 
were placed in the prolongation of the diameter of the wheel (jig. 3), but in 
this position their power to retain the water ceased when the bucket became 
horizontal. Then the buckets were inclined, as seen in gf, jig. 6; but this 
arrangement was liable to the objection that the capacity of the buckets 
was much diminished, while the wheel itself was made very heavy. Sub- 
sequently the buckets were formed with two inclinations, as seen at Mo F, 
jig. 6, which insured the advantages without the disadvantages of the 
inclined bucket. 
Under-shot wheels, as already remarked, are those in which the water 
acts only by impulsion or concussion. There are many varieties of the same. 
Pl. 15, jig. 5, is a form often used in small but rapid streams. Where a 
stronger wheel and larger bucket is required, the wheel seen in jigs. 3 and 
4 is used; in this case, it will be seen that the buckets do not project beyond 
the sides of the wheel as in the former case. 
Pl. 15, figs. 1 and 2, are a side and front view of an iron over-shot wheel ; 
E is the flume which conveys the water to the wheel; 7 is the gate which 
regulates the flow of the water, and is worked by the screw ¢; c is the 
bevel-wheel which transmits the power to the machinery. gs. 3 and 4 
are vertical sections and plan of iron breast-wheel; a is the gate, raised and 
lowered by the pinion @, worked by crank; c is the cog-wheel which drives 
the machinery. In jig. 5 the gate © is raised by the pinion 6, and guided 
by the roller c¢. igs. 7 to 18 show the details of an under-shot wheel of 
approved modern construction, the principal parts of which are of cast-iron ; 
Jig. 7 is a side-view, showing the driving circles and the wheel which transmits 
the power; fig. 8 is a vertical section of one half of the whole; fig. 9 is a plan 
showing the apparatus for raising the gate and the driving-wheel L; jig. 10 
is a vertical section through the axis; jig. 11 a portion of the annular disks 
which support the ends of the buckets, showing the grooves which receive 
the same; jig. 12 shows the construction of the buckets on a large scale ; 
Jig. 13, section through one of the buckets; jig. 14 is a section of the apron 
or gate, furnished with shelves forming shutes at different heights, that the 
water may be delivered horizontally upon the wheel, whatever may be the 
height of the water in the flume ; fig. 15, pillow boxes of main shaft; jig. 16, 
the same seen from above; jig. 17, the box forthe shaft which raises the apron; 
jig. 18, front-view of the same. The same letters indicate corresponding 
parts in all the drawings. 4 is the hollow iron shaft, running in boxes, B, upon 
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