6 2 



Proceedings of the Royal Irish Academy. 



to 1910 inclusive. The observations which are made at noon, 4 p.m., 8 p.m., 

 midnight, 4 a.m., and 8 a.m., give the direction to sixteen points, and the 

 intensity on the Beaufort scale. The accuracy of these observations, notwith- 

 standing the official instruction that the lightkeeper " should be prepared to 

 swear to it in a Court of Justice at any time," is unfortunately from the 

 scientific standpoint not very satisfactory. No instruments were used in 

 making the observations ; and of course the personal equation in its fullest 

 sense must have played an important part. This was made evident in many 

 ways in the course of the study of the records ; thus, for example, as regards 

 observations on direction, we find, on summarizing the six daily returns for 

 the month of June extending OA r er seventeen years, the following numbers 

 for the sixteen points of the compass : — 



N. I NNE. I NE. I EXE. I E. I ESE. I SE. I SSE. I S. 



ssw. 



36 



SW. 

 429 



wsw. 



53 



W. 



536 



WNW. I NW. I SSW. I Calm. 

 47 414 59 60 



It will be seen that the main points X, NE, E, SE, S, SW, W, WW were 

 unduly favoured by the observer at the expense of the intermediate directions. 

 A corresponding lack of discrimination was found in the records of the 

 intensity of the wind according to the Beaufort scale. 



This scale, it might here be pointed out, represents, by numbers from 

 to 12, the intensities of winds from a calm to a hurricane. The following 

 table gives the description and velocity of wind corresponding to the Beaufort 

 number as recently 1 decided and accepted by meteorological authorities : — 



Beaufort Number. 



Description of Wind. 



Velocity in miles 

 per hour. 







Calm. 



Less than 1. 



1 



Light air. 



1-3 



2 



Slight breeze. 



4-7 



3 



Gentle breeze. 



8-12 



4 



Moderate breeze. 



13-18 



5 



Fresh breeze. 



19-24 



6 



Strong breeze. 



25-31 



7 



High wind. 



32-38 



8 



Gale. 



39-46 



9 



Strong gale. 



47-54 



10 



Whole gale. 



55-63 



11 



Storm. 



64-75 



12 



Hurricane. 



Above 75. 



See Meteorological Office Handbook for Observers. 



