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ON THE PROGRESS IN ANEMOMETRICAL RESEARCHES, 97 
mal lines falls in summer in the ocean, and in winter on the continents. In 
the same manner the occurrence of two isolated closed spaces in Hindostan 
converts the trade into a monsoon, while in summer northerly breezes (the 
Etesian winds), which have their point of attraction in Africa, blow over the 
Mediterranean. Hence the sub-tropical zone is wanting in Asia, while the 
smallness of the alteration in the position of the isothermal lines, 12° to 20° 
Reaumur, or 59° to 77° Fahrenheit, in the Atlantic, fixes it to a definite place. 
Hence also the distribution of temperature in the thermic wind-rose is of an 
opposite kind according as the place is situated on the eastern or the western 
side of a continent. 
In conclusion, the results here communicated will, I trust, appear to justify 
the expression of a wish, that when meteorological observations are pub- 
lished, their value may not be lessened, ashas so often been the case heretofore, 
by publishing only the means of the seasons and of the year; but that the 
monthly means will be also published. 
On the Progress of the Investigation on the Influence of Carbonic Acid 
on the Growth of Ferns. By Dr. DAUBENY. 
Dr. Dauseny reported that the ferns were now growing in a large excess 
of carbonic acid, the amount of which had been ascertained daily during the 
last month. He however suggested some modifications in the form of the 
apparatus, the object being to secure the gas from leakage more perfectly 
than had hitherto been done. 
Notice of further Progress in Anemometrical Researches. 
By Joun Puiuuips, F.R.S. 
REFERRING to the report on this subject, presented to the Southampton 
Meeting of the Association and printed in the Transactions, the author reca- 
pitulated the steps of the investigation by which he had been conducted to 
propose the evaporation of water as a measure of the velocity of air-move- 
ment. In the former researches, the conclusion which may be drawn a@ 
priori from Dr. Apjohn’s formula for the relation of the temperature of the 
dew-point to that of an evaporating surface, was verified ; and the rate of 
cooling of a wet bulb in the open air was found to be, eeteris paribus, simply 
proportional to ¢—¢' (¢ being the temperature of the air, ¢' that of an evapo- 
rating surface). The air-movement was found to affect the rate of cooling, 
nearly in proportion to the square root of the velocity; and thus by simply 
observing the rate of cooling of a wet bulb exposed to a current of air, and 
also the value of ¢—?', the velocity of the air current becomes easily calcu- 
lable. But this instrument is only an Anemoscope, of extreme delicacy and 
various applicability indeed, but incapable of being converted to a self-re- 
gistering Anemometer. 
It appeared to the author probable: that the rate of evaporation followed 
nearly or exactly the same law as the rate of cooling, the same reasoning in 
fact applying to each case. ‘This was tested by experiment in a great variety 
of ways, with instruments of extremely various forms, and with velocities of 
air-movement from 400 yards to 27,000 yards in the hour. The velocities 
of the wind were measured by a very lightly-poised machine anemometer of 
Dr. Robinson’s construction, but without any wheel-work, the revolutions 
being counted by the observer. 
_Inh the course of these experiments some apparently anomalous circum- 
stances in the rate of evaporation occurred to the author, but these he hopes 
to be able to interpret by further careful research, and finally to present in 
the compass of a few cubic inches an anemometer specially suited to measure 
and record the low velocities of wind, and furnish a useful complement to 
the larger machines already esteemed to be so important in meteorology. 
1848. H 
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