150 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1918. 



The first consideration is whether we have a sufficiency of wind- 

 power presented to us by Nature in these islands. It is the firm 

 conviction of the land dweller that nothing is more uncertain or in- 

 constant that the wind; and even the yachtsman would agree with 

 him that there are times of provoking calm and seasons of needless 

 activity. But neither the pedestrian nor the yachtsman is an ade- 

 quate authority. Calm as it may seem on land or on the surface of 

 the water, there is almost always a movement of the upper air. The 

 records of the too short-lived observatory on Ben Nevis disclosed 

 many occasions on which the observers had to struggle, roped to- 

 gether, against an 80-knot breeze at a time when scarcely a ripple 

 disturbed the surface of Loch Linnhe below. The records of Amer- ' 

 ican observatories confirm the conclusion that wind speed uniformly 

 increases with the elevation at which it is recorded. 



Even near the ground a condition of absolute calm is rarer than 

 would be anticipated. The longest continuous records that we 

 have are those of Greenwich Observatory, and they show an average 

 of 15 days calm in a year. But the Greenwich anemometer is not 

 favorably placed, being unduly sheltered from the south and south- 

 west, and it is quite certain that if it were 50 feet higher its record 

 of calm would be diminished. It seems probable that at a height 

 of 100 feet from the ground the existence of absolute calm is an 

 event of extreme rarity, and that if we could place a wind motor at 

 a height of 1,000 feet above the surrounding land we could rely on 

 its working for nineteen-twentieths of the time. 



The records of the meteorological office furnish us with actual 

 experience of the wind movement at different observing stations for 

 several years past. Some of these stations are, it is true, badly 

 placed, and their instruments are not so favorably situated as a 

 windmill would be ; but they are for that reason a safe guide to the 

 minimum of expectation. The following facts emerge clearly from 

 the records. Our prevalent winds are southwesterly, or a few points 

 on each side ; these occur on 188 days in each year. It is therefore 

 obvious that the area in which the best windpower is developed lies 

 on or near our western coasts. On the other hand, the easterly 

 breezes which are felt most strongly on the eastern coasts do not lose 

 quite so much of their force in passing over the midlands as do the 

 southwesterly winds, which are partially intercepted by the higher 

 ground of our western counties. There are, therefore, three zones 

 of decreasing wind strength, the western coasts being the highest, 

 next, the eastern coasts, and last, the midlands. Taking the average 

 of seven observatories near the western and southern coasts, it ap- 

 pears that a wind velocity of 4 miles an hour and upward is ex- 

 perienced during 7,450 hours out of the 8,760 hours in a year, and 

 the wind velocity most frequently recorded is from 15 to 17 miles 



