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Meteorological and Astronomical Notices, March 1851. By 

 Professor PiAZZi Smyth. Communicated by the Author. 



1. Determination of the true Strength and Direction of the Wind. — 

 In Osier's anemometer, which is so very generally employed wherever 

 a self-registering instrument is required, the strength and direction of 

 the wind are recorded by means which mark on the paper the indi- 

 vidual force of every little breath ; and as most strong gales consist of, 

 as it were, a multitude of small gusts, blowing some this way and 

 some that, the register of such a storm, in place of being represented 

 by a well-defined curved line, by which the law of increase and de- 

 crease of the wind could be satisfactorily made out, is shewn rather 

 by a broad band of oscillating pencil-marks, extending often over the 

 greater part of the scale, in some minute terms of which it is required 

 to ascertain the degree of the wind. In such a case, therefore, little 

 precision can be expected in the deductions ; and, what is more, there 

 is almost as much left to individual judgment in drawing a line 

 through the mass of the pencil-markings, as if there had not been 

 any instrumental method employed at all. 



Now, there are few practical purposes for which we require to know 

 exactly the nature of every little individual gust. If, for instance, 

 a farmer wished to ascertain the degree of resistance which his hay- 

 stack should be capable of opposing, so as not to be overturned in a 

 violent gale ; then the minute results of the hard metallic surface of 

 the pressure-plate of Osler'*s anemometer would not give him a true 

 idea of the impact of the wind on the centre of gravity of the stack, 

 when that wind has to strike, first of all, the loose feathery side of 

 the straw, and then to be transmitted to the middle of the mass 

 through such a large quantity of elastic material. 



Again, if the effect of the wind on the gr^^at Exhibition building 

 were sought, although the surface there is of the same nature as 

 that of the anemometer plate, still the enormous extent of the build- 

 ing would have a powerful effect in equalizing the separate gusts ; 

 and, as a whole, it would only be affected by the mean of them. In 

 the case of a ship, too, we require not only the effect of the wind 

 over a large surface, but during a considerable space of time, and 

 therefore the mean, not the particular, strength : and in meteoro- 

 logical questions, it is of more importance to ascertain the general 

 movement of translation of the air than any individual features of 

 very small portions of it. 



But while some instruments of the cumulative kind for giving the 

 mean effects of the strength of the wind, as with Whewell's anemo- 

 meter, have come into use, there was not only more difficulty in 

 applying such a principle to the direction of the wind, but a fear 

 was expressed that, if it were accomplished, we might lose the records 

 of some of those important shiftings of the wind through an angle of 

 180°, which occur when the centre of a hurricane passes over the 

 VOL. L. NO. C. — APRIL 1851. Z 



