254 REPORT — 1844. 



or some line parallel to those corresponding to intermediate points, such as 



N.N.W., N.W., &c. 



The force of the wind is recorded by the action of a pressure-plate T, 

 which by the vane V is presented to the direction of the current ; this plate 

 is sustained by two bars moving on friction rollers, and working through the 

 hollow vane staff, as shown in the figure, the pressure of the wind on this 

 plate is b}' these bars communicated to a spring inclosed in a tube t, the 

 whole of which is sheltered by an outer case ; as the spring becomes com- 

 pressed it pulls on a wire-line not seen in the figure, which line, by means of 

 small pullies, is led through the hollow vane staff", and finally brought to pull 

 upon the spring lever v, and thus draw the pencil 2' towards tlie rod : the 

 height to which the pencil becomes raised on the graduated scale b d, fig. 1, 

 represents the pressure of the wind in lbs. on an area of one square foot. 

 The kind of trace left on the register is indicated in fig. 1. 



The amount of rain is recorded in a somewhat similar way by the pencil 3' 

 attached to the spring lever t;'. The rain, when it descends into the receiver 

 R, is conducted into one of the compartments of a gauge ^o^, balanced on an 

 axis and sustained by a second balance,, gn ; as the water collects, this second 

 balance, o^ n, begins to move and so raises the bob h. Now the spring lever u' 

 carrying the pencil 3' is acted on by this bob, and hence the pencil is pushed 

 forward upon the graduated scale a c, fig. 1, according to the quantity 

 of water collected in the gauge; when the quantity becomes equal to ^ of 

 an inch in rain, or to a certain number of cubic inches on a foot square, 

 then the little gauge g oversets, the water is discharged, and an opposite 

 compartment of the gauge is brought under the pipe at g ; the pencil of 

 course now returns to its first position, and begins again to rise on the scale 

 as the rain collects; a trace of this is shown in fig. 1; and it may be easily 

 imagined that the more rapid the fall of rain the sharper will be the angles 

 caused by the trace of the pencil ; on the contrary, if the fall of rain be gra- 

 dual and slow, the elevating or diagonal lines will be drawn out into a con- 

 siderable length, as shown in the figure. 



It is therefore evident that as the register M, fig. 1 , becomes constantly and 

 hourly drawn along under the three pencils 1 ', 2', 3', a continued record or 

 trace of the direction and pressure of the wind, together with the amount of 

 rain, is left on the paper, an illustration of which is given in fig. 1. 



The table on which the register-frame is supported is five feet long and 

 about three feet six inches wide, with a strip cut out of the centre fifteen 

 inches wide to admit the board M, and allow of its being gradually drawn 

 along under the pencils. 



The register-papers are about twenty-two inches long and a foot wide, and 

 are placed daily on the board M. 



Such are the principal features of the instrument which has been set up 

 by the British Association at Plymouth, and also in Scotland and Ireland, for 

 recording observations on the winds. 1 have not thought it requisite to enter 

 upon any lengthened explanation of the several mechanical adaptations, or 

 to complicate the figured description of it by lines representative of all the 

 subordinate parts, as this would have onl)' embarrassed the general account 

 of it without any adequate return. 



The use of this anemometer, such as just described, has been much im- 

 peded by the following circumstances : — First, the action of the pressure- 

 plate is liable to frequent derangement from the violence of the wind, by 

 which the wire-line communicating motion to the pencil below is broken ; 

 it is likewise from other defects in construction frequently uncertain, so that 

 the register of the force is deficient ; the tendency of the vane also to oscil- 



i 



