416 
DE. T. E. EOBINSON ON THE EEDUCTION OF ANEMOGEAMS. 
maximum in August and a slight minimum in November. The variation is greater 
here than in the horary columns, being for hour 15 = 6 m, 56. The largest W is at 
March 15 h =6 m, 56 ; the least at May 15 h =(H)0. 
The law of S is simpler ; it has one maximum in December and one minimum in 
July; its range, too, is something greater, being in hour 20 = 6 m, 98. The greatest 
magnitude =8 m *285 at December 4 h , its least = 0 m -82, July 19 h . There is a general 
agreement in the change of the two components, with one striking exception, the 
maximum and minimum which W has in March and April. Such a general agree- 
ment might be expected, for any air coming from the south must have a westward 
motion due to the greater velocity of the earth’s rotation in a southern parallel. This 
anomaly, if real, may be caused by the geographical conditions to which I have already 
alluded. To them also maybe referred the fact that at May 15 h W=0, though 
S=2 m, 41, from which a sensible magnitude of the other might be expected. It must, 
however, be observed that some of the changes exhibited in this Table can scarcely be 
regarded as periodical. I have already pointed out that from the very great dis- 
cordance of individual observations it is evident that a much greater number of them 
than is afforded by a period of seven years is required to eliminate the barometric and 
hygrometric influences. Yet these disturbances might be expected to be distributed 
with some uniformity through the day; while the changes from hour to hour are 
sometimes considerable. Thus in February 9 h to 10 h AW=0‘89; 16 h to 17 h AW 
= — 0*90,; March 10 h to ll h AW=-1T5 ; 14 h to 15 h AW=094; April 10 h to ll h 
AS= — 0'71 ; December 10 h to ll h AS=086. These are the largest; and it deserves 
notice that they occur in winter months ; in summer there is much less abruptness 
of change. 
It occurred to me that some of these irregularities might be due to errors in the 
records of velocity ; but this seems quite improbable. Such errors could only arise from 
three possible causes. 
1. Referring to my description of the anemograph in the ‘ Transactions of the Royal 
Irish Academy,’ vol. xxii., it will be obvious that the track of the recording pencil might 
be excentric to the brass disk which carries the paper. It was carefully adjusted when- 
ever the clock was cleaned, but was liable to derangement from rough handling. The 
error which would thus arise was avoided by an easy adjustment, which made the edge 
of the reading alidad coincide with the right line drawn by the pencil when the clock 
was wound up. It will easily appear that the readings so made are true. 
2. The paper may be excentric to the centre of rotation. Let e be its excentricity, 
e that of the pencil, Q the reading of any distance from the winding line, ip the angle 
between that line and the line of the two centres, the correction for 6 
— s(sin\J/ — 1) — (e sin\[/(— — 9)\ 
