io6 



NA TURE 



[May 31, 1906 



foliagcd sea-cliffs"; and that the peregrine falcons 

 still occupy the ancient eyries in which they were 

 protected for 300 years, although now their names 

 are. strangely enough, not among those scheduled in 

 the Wild Birds Protection Act. On the other hand, 

 they will note with regret the extinction of the rock- 

 dove and of the .shearwater (which derives its name 

 from the island), which were once so abundant among 

 its cliffs. 



This volume, if not perhaps quite up to the standard 

 of some others of the series, is a conscientious and 

 careful contribution to the natural history of Man. 

 It is beautifully illustrated by two maps,' as to the 

 excellence of which no more need be said than that 

 they are by Bartholomew, of Edinburgh, and by 

 fifty full-page blocks of Man.x scenery (rnost of them 

 of favourite nesting-places of different species), a 

 specimen of which, by the publisher's courtesy, is 

 here reproduced. F. 



THE BEAUFORT SCALE.^ 

 A BOUT a hundred years ago. Admiral Beaufort, 

 -'^ having felt the want of some scheme bv which 

 the winds could be classified according to their force, 

 devised a plan which has been in uninterrupted use 

 ever since. In the absence of mechanical anemometers 

 he had to trust to personal experience and the observed 

 effects of wind on the objects moved by it. As a sailor, 

 he naturally selected ships as the' objects moved. 

 Calling a calm zero, and representing a hurricane, or 

 a wind in which no ship could carry any canvas, 

 by 12, he endeavoured to assign the intermediate 

 numbers to winds the force of which could be 

 gauged by the amount of sail that a well-con- 

 ditioned ship of specified rig could carry. In the 

 lapse of time sailing ships altered their rigging or 

 disappeared altogether, with the result that the 

 gallant Admiral's nomenclature became obsolete or 

 unmeaning. Anemometers depending upon the appli- 

 cation of some mechanical principle came into general 

 use, and from the fact that these instruments gave 

 a continual record, right or wrong, their register 

 tended to supersede a plan, which relied simpTy on 

 tradition and probably varied in individual observers. 

 But it has always been felt that there existed some 

 relation between the records of the anemometer and the 

 Beaufort Scale, and various authorities have attempted 

 from time to time to bring the two into accord, or to 

 supply the means of expressing any given number in 

 the Beaufort Scale as velocity reckoned in miles per 

 hour. These well-meaning attempts have not enjoyed 

 the unquestioned confidence of meteorologists, nor have 

 they ensured uniformity in practice. Of late the 

 Meteorological Office has instituted a rigorous inquiry 

 into the estimates of wind force as made in the Beau- 

 fort plan and as recorded by anemometers, and have 

 now issued their report. 



A preliminary question presents itself to which it is 

 difficult to give a completely satisfactory answer. Is 

 the Beaufort Scale worth preserving? or, in other 

 words, relying as the scale does on personal experi- 

 ence, is it capable of being reproduced with sufficient 

 accuracy to ensure the maintenance of constancv in 

 all circumstances and in all localities? This question 

 must have presented itself to the Meteorological Office 

 and been answered in the affirmative. The decision 

 taken is probably justified. In many positions at sea 



1 "Report of the Director of the Meteorological Office upon an Inquiry 

 into the Relation between the Estimates of Wind-Force according to 

 Admiral Beaufort's Scale and the Velocities recorded bv Anemometers 

 belonging to the Office; with a Report by G. C.Simpson, M.Sc.and Notes 

 by Sir G. H. Darwin, W. H. Dines, and Commander Hepworth." (Printed 

 for His Majesty's Stationery Office. London, 1906.) 



It is not possible to use mechanical anemometers. In 

 lawsuits and Board of Trade inquiries the vocabulary 

 of the Beaufort Scale is in frequent use, and nautical 

 assessors have to attach a definite meaning to it. On 

 the other hand, are we sure that the automatic regis- 

 tration by anemometers has been correctly interpreted? 

 Dr W. N. Shaw himself raises the question whether 

 the hourly velocity is a suitable element for com- 

 parison. It is probably the best that can be done, but 

 it may be that we are trying to compare a scale of 

 doubtful utility with a record that is onlv imperfectly 

 understood. 



The anemometers in use in this country are of two 

 kinds, that known as the Robinson, which gives us 

 with accuracy the number of times that a system of 

 hemispherical cups rotates in any specified interval, 

 when mounted in a particular manner. The error, 

 or possible error, in the use of this apparatus enters 

 when we pass from the velocity of the cups to that of 

 the wind. For years it was assumed that the wind 

 velocity was three times that of the cups, a round 

 number which of itself suggested that it was a rough 

 approximation. The factor 2-1 or 2-2 is now proposed 

 as more appropriate. But there is this further diffi- 

 culty : that while the velocity of the wind in an hour is 

 not constant, the method of registration smooths out 

 the irregularities, so that the \-ariations in the velocities 

 become indistinguishable in the record. The other 

 form of anemometer, known as the Dines Pressure 

 Tube, shows the variation in the wind velocity by 

 recording a succession of oscillations of considerable 

 magnitude. The trace is such as results from a pen 

 moving vertically with comparative rapiditv over 

 paper moving more slowly horizontally. To determine 

 the mean velocity from this trace is a matter of some 

 uncertainty. The eye naturally selects a line which 

 may be taken as representing the mean velocity during 

 the interval under examination. But the number of 

 miles per hour indicated by the position of this line 

 can only be known from experimental inquiry. These 

 experiments have been conducted bv Mr. Dines in an 

 exhaustive manner, but the results must nevertheless 

 be considered as empirical. It is upon these ex- 

 periments that the constant for the Robinson anemo- 

 meter has been changed. Finally, therefore, the 

 problem resolves itself into reading the results derived 

 from the experiments of Mr. Dines into the phenomena 

 observed by sailors and others in deciding on the 

 numbers used in the Beaufort S'cale. 



But assuming that the hourly wind velocity is 

 correctly known at any moment, it would seem a 

 tolerably simple matter to assign to each of the Beau- 

 fort numbers the corresponding wind velocity. We 

 have simply to take the mean value of the velocities 

 for all winds estimated as being of a given Beaufort 

 number to get a scale equivalent in miles per hour. 

 This has been done more than once, and a table of 

 such equivalents has been issued under the sanction 

 of the Board of Trade. Such a simple solution, how- 

 ever, by no means disposes of all the difficulties. Prof. 

 Koppen pointed out that a different scale of equivalents 

 was obtained, when the mean value of all the velocities 

 assigned by estimate as of a given Beaufort number 

 was taken, from that which resulted from taking the 

 mean of the Beaufort numbers corresponding to given 

 velocities. The first method of treatment may be 

 described as that of Curtis, the second as that of 

 Koppen. To explain the cause of the difference 

 betwen the two methods was the problem submitted 

 to Mr. G. C. Simpson, and very ably he has dealt 

 with it. Unfortunately we cannot follow him in his 

 details ; we can onlv point out some of his results. The 

 following table shows the relation between the Beau- 



NO. T909, VOL. 74] 



