ON A SELF-RECORDING ANEMOMETER, 307 
equal to fifty miles of wind. On the same fitting, and moving with it, is the 
wheel z, working into its fellow 7, which is fixed on and gives motion to the 
axis of tle screw-pencil cylinder A: these wheels are kept in gear by the 
radial arms 0,0. The pitch of screw for the velocity-pencil is equal to a 
seale of fifty miles upon the paper on the cylinder C. By this method I get 
a very open scale within a small space. 
Any change in the direction of the wind is communicated to the mitre 
wheels ¢, c, fig. 2, Pl. XX., fixed to the shaft K, onthe other end of which is 
the wheelZ; from this, by two others, m, m',a corresponding motion is given 
to the wheel x, fixed on the axis of the screw-pencil cylinder B. I found it 
better to introduce the small wheels m, m, running on studs in the shifting arm 
P, for the direction-pencil, as the motion is variable. The pitch of the screw is 
equal to a scale of the cardinal points of the compass upon the paper. 
While these pencils are being acted upon by the wind, the clock gives a 
uniform motion of 3 in. per hour to the cylinder C, upon which the paper is 
. fastened,—in connexion with which I beg to say that, as the clock must be 
wound up daily, and as the time occupied in changing the paper is not 
more than two or three minutes, [ think it better to do so than to have a 
continuous roll of paper lasting many days, which certainly is not so conve- 
nient for reference as the daily record of 12 inches by 8 inches. 
By using the spiral form of pencil, I overcome the trouble attending the 
old method, viz. the pencil shifting off the scale. To ensure registration, it is 
usual to have three scales upon the paper, and set the pencil on the centre ; 
but even then, should the wind shift twice round in one direction, it ceases to 
indicate: by my method it must at all times register upon the one scale. 
Fig. 5, Pl. XX., is a copy of a sheet from the Kew Observatory, in which the 
advantage is evident. 
In conclusion, I would suggest that as the pencils are kept upon the paper 
by their own gravity, requiring no attention and being as long as the trace 
they make, they will last a long time. The space required for the instrument 
not being morethan18 inches x 8 inches, I should recommenditsbeing placed 
upon a bracket as close to the roof of the building as convenient, similar to 
the anemometer at Kew, it being very advantageous to keep the shaft as short 
as possible. 
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