ASEMO'METKU. 



ANEMOTUKTER. 



M 



over * fixed cylinder, producing thereon trace of variable length, 

 according a* tie wind varies in velocity. The surface of the fixed 

 cylinder in divided into ixtoen or thirty-two equal part* by meuis of 

 Tertieal lino, the space* between which correspond with the point* of 

 the compaw, tad between or upon theee divisions th pencil is moved 

 by mean* of the vane, and the trace that it leaven (hows the 

 ion of the wind. The pencil, however, baa two motion*, one 

 from above, downward* ( 1 0,000 revolution* of the fly cauaing the pencil 

 of an inch), and thi* motion increase* a* the wind blown 

 atrungTy, and by the extent of its depression reguter* the whole 

 mt of wind that ha* been blowing. The other motion depends on 



_ i of the quarter from which the wind blown ; the IH-IH il and its 

 frame are carried round by the vane, so a* to register the rftnr/i'n of 

 the wind. Thus, if the fly revolve in the simple proportion of the 

 velocity of the wiiul, the trace marked by the pencil describe* a space 

 proportional to that which a particle of air would describe in a given 

 direction in a given time, taking into account the strength of the wind 

 and the time for which it blows. The constant vareriny of the wind 

 causes the pencil to describe, not a single line, but an irregular l'i ond 

 path, something like the shading* in the coast of a map. The middle 

 of this line will give the mean direction of tin- wind, while its length 

 will be in proportion to the product of the velocity of the wind and 

 the length of time during which it blows in each direction, which 

 product is called ite Integral force. 



A great objection to the above form of anemometer is the amount 

 of friction involved in the method of converting the rapid motion of 

 the fly into a slow descending motion, and hi the mode by which the 

 pencil is made to move against the fixed cylinder. Osier's anemometer 

 has some advantage* over Whewell's. This instrument trace* the 

 direction of the wind and ite pressure on a given area, together with 

 the amount of rain, on a register sheet divided into twenty-four por- 

 tion*, corresponding with the twenty-four hours of the day. The 

 action of this instrument will be understood by referring to ri;i. 4, 



Fig. 4. 



which represent* the part* adjoining the register-paper. The central 

 |..r'i.,n of thi* paper ha* a aerie* of line* corresponding with the 

 cardinal point* of the compos*, for indicating the dine/inn of the wind. 

 The upper part of the paper ha* a series of linn corresponding with 

 the pretntrc in jxiunds on the nqnare foot, while the lower part of the 

 paper ha* a aerie* of lines corresponding with given quantities of rain. 

 There is also a series of twenty-four vertical lines, corresponding with 

 the twenty-four hours of the day, *o that a new register- |nper, being 

 properly placed on a board, i* carried along upon friction-rollers, by 

 mean* of a clock, behind the three pencil* A, n, c, which may be 

 regarded a* the indexes of the machine. The pencil n, which marks 

 the direction, I* operated on by means of a set of vanes (Jig. 5), turn- 

 ing vertically in a plane at right angle* to that of the pressure-plate ( r, 



fg. B), and driving a cog-wheel, which rolling on a fixed cogged circle, 

 turns the rest of the apparatus round, so a* to present the edge* of 'le- 

 nt-. J. 



sails to the current when it is no longer turned by it either way : 

 under these circumstance*, the pressure-plate is placed at right angles 

 to the vanes, and is acted on with full effect by the wind. As the 

 vane or cap turns in the direction of the wind, a spiral worm on til- 

 shaft near it* lower end raises or lowers the fixed nnt I, fn.ni which 

 springs the arm which carries the pencil B ; this pencil traces a mark 

 on one of the long lines of the reguter when the wind is blowing from 

 one of the cardinal pointe, or between those lines, if it be blowing from 

 intermediate points. The pressure-plate is made to face the wind by 

 means of the vane or cap. It is suspended by means of four springs, 

 which yield to gentle winds, while a stronger spring receives the 'more 

 violent pressure of a high wind. The motion of the plate is trans- 

 mitted to the register-paper by means of a wire connected by the 

 bell-crank J with another wire, which descends through tin- hollow 

 upright shaft, and is kept stretched by a spiral spring. This wire 

 carries the upper pencil c, which of course descends lower in propor- 

 tion as the pressure-plate E is pushed back, and returns to the top ... 

 the paper when the pressure ceases. In this way, the distance to 

 which the pencil is depressed shows, by means of a number of 

 irregular parallel lines, the pressure of the wind in pounds on the area 

 of one square foot, or it* velocity in miles per hour. For registering 

 the rain, the pencil A is attached to a lever A F, ///. 4, whi< h is 

 by the following contrivance : A rain-receiver, D, i* placed on the roof 

 of the house, and the water which pours into it i* conducted into one 

 of the two divisions of a gouge, o H, balanced on an axis and .-u).|...i t, ,1 

 by a second balance : as the water accumulate* in o (for cxamp! 

 second balance begins to descend, and thus raises the upright rod to 

 which the lever r A is attached, when the pencil, being raised with it , 

 makes a mark on the paper, which represent* the quantity of water 

 collected in the gauge. When this quantity in equal to a certain 

 depth of rain or to a certain number of cubic inches on a square foot, 

 the gauge become* upset by the weight of water, the water in thrown 

 out, and the other compartment, B, is brought under th<> pi]..- : th.- 

 effect of which motion is to send the pencil to th. 1 ...itom --t tli- 

 and it only beguu to rise again when more rain is collected. Of . 

 the heavier the rain, the sharper will be the angles formed 

 trace of the paper; whereas, if the rain be gentle, the elevating or 

 diagonal line* will be drawn out to a considerable length ; and lastly, 

 if there be no rain, the pencil will trace a horizontal line, such as in 

 represented in/i/. 4, from vi. to vuij, and from xj to I. 



Thus it will be seen, that as the register-paper is being constantly 

 moved forward* by the action of a clock, the three ]>eucils mark the 

 direction and pressure of the wind, together with the amount of rain. 

 The register-paper may be ruled for twenty-four hours, or for a week, 

 and it may be placed vertically, as at the hange, London, in- 



laid horizontally on a table, M at the Meteorological Observatory at 

 Greenwich, where the reguter, being on a larger scale, i* el 

 every day. Mr. Osier ha* further improved his anemometer in the 

 following manner: A sheet of plain paper, placed in the instrument 

 \inder a registering pencil, is moved forward by rotating hemispherical 

 fans, at the rate of one inch for every two miles of air that pauses ; 

 this same pencil, having a lateral motion given to it by a vane, records 

 the point of the compaa* from which the wind blows; :md .. 

 hammer descending every hour, strikes ite mark on thn margin of the 

 paper to exprw* the time. Thus in a single line are given, 1st, the 

 length of the current; 2nd, the direction of the current; 3rd, the 



