244 REPORT — 1844. 



ment of the air both in velocity and direction, together with other periodical 

 movements of no less importance to the present state of meteorology. 



With this view 1 have laid down in the annexed tables the general results 

 of this anemometer for certain great periods of time. In Tables I. II. III. 

 will be found the respective quantities of wind to sixteen points of the compass 

 for the successive months of the years 1841, 1842, and 1843, together with 

 the total amount for each year. 



In Table IV. will be found the mean quantity of each wind for the three 

 years, as deduced from the sums of Tables I. II. III. 



In Table V.are given the effective winds reduced to eight points of the com- 

 pass, by subtracting the lesser amount of wind from the greater for opposite 

 directions, so that by the prevalence of certain winds over others, eight 

 points of the compass vanish. 



In Table VI. will be found the mean results of the three years, also re- 

 duced to eight points of the compass in a similar way. 



Table VII. contains the mean quantity of wind for each of the four sea- 

 sons, as deduced from the mean results of Tables I. II, and III. March, 

 April and May are here considered as months of spring; June, July and 

 August summer months; September, October, November, months of Au- 

 tumn ; and December, January, February, winter months. 



Table VIII. shows the reduction to eight points as before. 



Table IX. comprises the two months' observations for the year 1844, at 

 which time they were discontinued. 



These Tables enable us to deduce, by the method just explained, the mean 

 direction and velocity of the wind for certain periods of time, as shown by 

 this instrument, and which is effected in Plates XXXV. and XXXVI. 



In Plate XXXV. figs. 6, 7, 8, will be found the eight effective winds of the 

 years 1841, 1842, and 1843, laid off for each year as a polygon of forces, and 

 in fig. 9 the mean results of these years are laid off in a similar way. 



In constructing these figures the winds have been taken in the order of 

 following points of the compass, the forces being deduced from Table V. 

 The effective winds in this order for the three years, together with the mean, 

 are given in Table X. 



It will be seen by these figures that comparative values of the wind in ve- 

 locity and direction have been arrived at ; and that an instrument, if sufficiently 

 perfect in its mechanical details on this principle, would be of great import- 

 ance to meteorology. 



The result of 1841 (fig. 6) gives a mean direction N. 15° east, the relative 

 magnitude of the resultant on the scale of measure being 4180. 



The result of 1842 (fig. 7) gives a mean direction N. 12° west, the relative 

 magnitude of the resultant being 3800. 



The result of 1843 (fig. 8) has a mean direction N. 2° east, the magnitude 

 of the resultant being 2810. 



The mean result (fig. 8) has a mean direction N. 1° east, the magnitude of 

 the resultant being 3.500. 



Although these difierent resultants represent the relative spaces which a 

 particle of air would have passed over in each of these years in the given 

 directions, if acted on by a single force equivalent to all the others, yet they 

 do not give us any information of the actual velocity of the wind in these 

 different years. Now it is most desirable, if possible, to discover this, since 

 for the future progress of anemometry it is not only relative but absolute 

 values we require. 



The method by which I proposed to arrive at this has been already 

 pointed out in the Reports of the Association for 1842, and although to a 



