Ventilation : a text-book to the practice of the art of ventilating buildings with a supplementary chapter upon air testing / by William Paton Buchan.

  • Buchan, William Paton.
Date:
1891
Catalogue details

Licence: Public Domain Mark

Credit: Ventilation : a text-book to the practice of the art of ventilating buildings with a supplementary chapter upon air testing / by William Paton Buchan. Source: Wellcome Collection.

    28/298 (page 16)
    From to 6 ft. a second ordinary speed of current up a chimney, or about 3 or 4 miles an hour. In good ventilation the change of air should take place without being perceptible. the Sanitary Institute at Worcester in 1889, on Winds, with some Remarks on their Sanitary Effects. Inter alia Dr. Tripe said :— '' The relations between wind velocities and pressure were until lately in a chaotic state of confusion, but, thanks to Mr. Dines and his late father, we now have some definite information on the subject. They erected a whirling machine, driven at various rates by a steam engine. The machine consisted of a long bar, supported by stays, carrying plates of different shapes and sizes, and, for the purpose of comparison, a uniform velocity of 20*86 miles per hour was finally adopted. The result showed that with a velocity of 21 miles per hour the pressure exerted upon a plane area of a fairly compact form is about \ \ lbs. per square foot. As the wind pressure up to a velocity of 70 miles per hour has been found to vary in these experiments as the square of the velocity, the pressure with any intermediate velocity can be readily calculated. If we take the pressure of 1 lb. per square foot as a basis, it is found that a velocity of 17 miles per hour gives this pressure. This varies, however, to a certain but small extent, accord- ing to the size and shape of the plate. As Beaufort's scale is used not only by seamen, but by most meteorological observers, to express the velocity of the wind, I give the table adopted by the Meteorological Office, and used in the com- parison of weather with storm signals, and by captains at sea: — Force. Approximate Beaufort's Velocity. Scale. Miles per hour. 0. Calm 0—5 1. Light air, or just sufficient to give steerage way . 6—10 !Or that in which a well- / conditioned man-of-war, \ I—2 knots 11—15 with all sail set, and clear < 3—4 16—20 full, would go in smooth 15—6 21—25 water from V 5. Fresh . . /Royals, &c. . . 26—30 6. Strong . . • ] Qr ^at jn ( Single-reefed topsails I Th Ti Vi I an(^ topgallant sails . 31—36 7. Moderate gale f wm£n .® ) Double-reefed topsail > couid J.ust { jib, &c. . 37—44 8. Fresh „ ( ^^^u i Triple-reefed topsails, 9. Strong ,, ! an(* ^7 [ Close-reefed topsails \ and courses . . 53—60 10. Whole gale, or that with which she could scarcely bear close-reefed maintopsail and reefed foresails 61—69 11. Storm, or that which would reduce her to storm staysails 70—80 12. Hurricane, or that which no canvas could withstand 80 miles and upwards