Some data given by Wolff on mills of the American type gave for the same quantity W =0-0004511' . From some of the data of experiments by Griffiths on mills of the American type used in pumping, the effective work in pumping when the mill was working in the best conditions amounted to from O-ooosu' to 0-000321' ft. Jb per sec. per sq. ft. In 1903 trials of wind-pumping engines were carried out at Park Royal by the Royal Agricultural Society (Journ. Roy. Agric. Soc. Ixiv. 174). The mills were run for two months altogether, pumping against a head of 200 ft. The final results on six of the best mills are given in Table II. A valuable paper by J. A . Griffiths (Proc. Inst. Civ. Eng. cxix. 321) contains details of a number of windmills of American type used for pumping and the results of a scries of trials. Table III. contains an abstract of the results of his observations on six types of windmills used for pumping:^eastern doorway of the Erechtheum, which formed part of the original building of 430 B.C., have lately been found; they were rectangular windows with moulded and enriched architrave, resting on a sill and crowned with the cymatium moulding. Of later date, at Ephesus, remains of similar windows have been discovered. Of Roman windows many examples have been found, those of the Tabularium being the oldest known. A coin of Tiberius representing the temple of Concord shows features in the side wings which might be windows, but as statues are shown in them they are possibly only niches. Over the door of the Pantheon is an open bronze grating, which is thought to be the prototype of the windows which lighted the large halls of the Thermae, as it was absolutely necessary that these should be closed so as to retain the heat, the openings in the gratings being filled with glass. In some cases window openings were closed with thin slabs of marble, of which there are examples still existing in the churches of S. Martino and the Quattro Santi Incoronati at Rome. Similar slabs exist in the upper storey of the amphitheatre at Pola; it still remains, however, an open question Table III. I. II. III. IV. V. VI. Diameter of wheel, feet Sail area, square feet Weather angle, outer ends „ „ inner ends Pitch of vanes, outer ends, feet „ „ inner ends, feet ..... Height of lift, feet Velocity of wind at maximum efficiency, miles per hour

Ratio of velocity of tips of vanes to velocity of wind Revolutions of mill, per minute Actual horse-power

In 100 average hours in a calm locality — Quantity of water lifted, gallons per hour In 100 average hours in a windy locality — Quantity of water lifted, gallons per hour 25 223 392 18" 47 38° 20 23-8 20-6 100 29-2 "•5 104 <43° 33-7 131 61-2 4-3 •93 50 0-018 495 816 70 77 6-8 0-098 306 629 5-8 -92 13-0 001 1 153 287 6-5 -82 13-3 0-025 13s 271 l6-o 201 36° 36-5 13-7 39-0 60 •65 7-5 0-024 259 525 14-2 K30" 25-7 8-2 66-3 7-0 91 12-6 0-065 267 540 lo- 81 2i 2i 17- 6- 38- 20 o 115 237 o 4 7 5 87 5 028 9-8 80 5o» 14° 22-4 7-2 307 6-0 •73 12-5 0012 145 270 I. Toowoomba; conical sail wheel with reefing vane. III. Perkins; solid wheel, automatic rudder. IV. and V. Altho automatic rudder.

Table IV. gives the horse-power which may be expected, according to Wolff, for an average of 8 hours per day for wheels of the American type. Diameter of