104 



GENERAL OBSEEVATIONS ON THE WINDS. 



0. 



1. 



2. 

 3. 

 4. 



^ Beaufort Notation. 



Velocity.* 



Calm 0-- 3 Miles per Hour, 



Light Air 8 



Light Breeze 13 



Gentle Breeze 18 



Moderate Breeze 23 



5. Fresh Breeze 28 



6. Strong Breeze 34 



7. Moderate Gale 40 



8. Fresh Gale 48 



9. Strong Gale 56 



10. Whole Gale 65 



11. Storm .... 



12. Hurricane 



75 

 90 



Just sufficient to give steerage way. 

 ^With which a well-con- >^ 



ditioned saUing Ship of 1 ^^ 3 knots. 

 War with aU sail set I 3 ^^ ^ ^^^^^^ 

 would go in smooth 

 water and " clean full," 

 from 



L 



5 to 6 knots. 



< 



To which she could just 



carry in chase, " full 



and by":— 

 J. Royals, &c. 

 Single-reefed topsails & 



topgallant sails. 

 Double-reefed topsails, 



jib, &c. 

 Treble-reefed topsails, 



&c. 

 Close-reefed topsails and 



courses. 

 With which she could 



scarcely bear close- 

 reefed maintopsail and 



reefed foresail. 

 Which would reduce her to storm stay-sails. 

 Which no canvas could withstand. 



For Ships Riooed 



WITH Double 



Topsails. 



6. Topgallant sails. 



7. Topsails, jib, &c. 



8. Reefed upper top- 

 sails and courses. 



9. Lower topsails and 

 courses. 



10. Lower main topsail 

 and reefed foresail. 



(15.) The wind over the land is found to be generally of much less force 

 and velocity than at sea, so that the Beaufort Notation was found incon- 

 venient for land purposes : Mr. Glaisher, therefore, proposed another 

 Notation for this use, which was adopted at Greenwich, Liverpool, and 

 indeed at most of the principal Observatories. It divides the Force into 

 the numbers 1 to 6, which have been proportioned to the Beaufort Scale, 

 as follows : — 



Glaisher Notation. 



1. Moderate (Beaufort Scale 1 — 2) 



2. Fresh ( „ 3—4) 



3. Strong ( „ 5—6) 



4. Heavy (Beaufort Scale 7 — 8) 



5. Violent ( „ 9—10) 



6. Tremendous ( „ 11 — 12) 



' (16.) From numerous observations made during the voyage of H.M.S. 

 Challenger, it was found that the Mean Hourly Velocity of the wind over 

 the ocean was 17^ miles, and on land only 12^ miles. 



(17.) The actual Force and Velocity of the Wind were calculated by Sir 

 W. Snow Harris, with an improvement of Lind's Anemometer, by which 

 he found air moving 20 feet in a second presses on 1 square foot with a 

 force of about 13 oz. avoirdupois, or at 50 feet per second it would support 

 a column of water 1 inch high, the pressure force increasing very nearly 

 with the squai-e of the velocity. With these data the Table on the follow- 

 ing page has been calculated : — 



* The Velocity of the Wind, given in Miles per Hour, is taken from the work entitled 

 "Aids to the Study and Forecasts of the Weather," by W. Clement Ley, M.A., published 

 by the Meteorological Council. 



