[74]

Table for Linds Wind Gage for Capt FitzRoy H. M. S Beagle.

2

Linds wind Gage =

The Force or pressure of the wind is ascertained by this Instrument in the following manner

- Fill the tub half full of water, and push the scale a little up or down until O of the scale when the Intr. is held perpendicularly below a line with the surface of the water in both legs of the Gage. – Then the turn the amount of the brass tank to the wind, and observe how much the water is depressed on one side, and raised in the other – The sum of the two is the height of a column of water which the wind is capable of sustaining at the time; and everybody which is opposed to that wind, will be pressed upon by a force equal to the weight of a column of water, having its base equal to the surface opposed, and its height equal to the attitude shewn by the gage. Hence the force of the wind upon any body where the surface opposed to it is known may be easily found and a comparison made betwixt the strength of the gale of wind and another – the use of the small connecting tube n b to check the undulation

[sketch]

(turn over

3

The force of the wind and its velocity may be estimated by reference to the following Table calculated partly by the Inventor, and partly by Dr Hutton

Height of water in scales	corresponding Force of wind on a square foot in Lbs avoird	Velocity in miles per hour	common designation of such a wind
1/40th	0, 130	5.7	gentle air
1/20th	0, 260	8	pleasant air
1/10th	0, 521	11.3	fresh breeze
1/2	2. 604	25.4	brisk gale
1	5. 208	36	strong gale
2	10. 416	50.8	heavy gale
3	15. 625	62	storm
4	20. 833	72	great storm
5	26. 041	80.4	hurricane or strong great storm
6	31. 750	88	great hurricane
7	36. 548	95.2	very great hurricane
8	41.667	101.6	}hurricanes which tear up hills &c &c
9	46.9	108
10	52.1	113.6
11	57. 293	119.2
12	62. 5	124

 

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Example of the use of the Instrument

Supposed altitude of column as per Inst 4,6 inches Nen ar havr by the proceeding Table

4 inches = 20.833 Lb

0.5 in = 2.604

0.1 in= 0.521

Sum 4.6 = 23.958 = force on (Foot)2 [squared]

[require] suppose equal 1.5 miles

Nen ar have

miles

1.0 = 5.208

0.5 = 2.604

Sum 1.5 = 7,812 Force

Remark 1/40 may be considered as 0, 025

1/20 --- as 0, 050

1/10 --- as 0, 100

1/2 --- as 0, 500

 

[3v]

It appears by the experiments of the learned Dr Hutton, that a square foot plane surface suppress a resistance from the wind when blowing with a velocity of 20 feet per second = 12 oz Hence taking a cubic foot of rain water at a 1000 ounces or 62.5 Lb the 1/12 part of which will be 5,2 Lbs nearly we have for every inch the surface of the water is raised a force equal to so many times 52 Lbs on a square foot hence 3 inches in gage gives 15.6 lb for the pressure or a Foot2 nearly