TRANSACTIONS OF THE SECTIONS, 37 
posed currents. Observations were made every minute, and sometimes every half 
minute, during short intervals, about the middle of the month of May, on days when 
the sky was clear, and during which there was consequently a great deal of solar 
radiation. The following are the principal results observed: the mercury in each 
thermometer rose and fell alternately during intervals varying from about half a 
minute up to six minutes. The extent of the oscillations was sometimes very con- 
siderable in thermometers freely exposed to the air; the mercury sometimes rising 
or falling nearly three degrees in three minutes. In general the thermometers 
exhibited fluctuations of temperature, the intensity of which diminished the more 
they were protected from the influence of circulating currents in the air. The great- 
est fluctuations were presented by thermometers with blackened bulbs exposed in the 
sun. This arose from the circumstance that the blackened bulbs, by acquiring a 
high temperature, became themselves disturbing agents in the calorific conditions of 
the surrounding air. Evidence of similar phenomena appears to be presented by 
the curves of temperature obtained by the aid of photographical registration at the 
Radcliffe Observatory in Oxford. The application of photography to the continuous 
registration of atmospherical conditions, has been carried out in that Observatory 
with so much care, and has been attended with such remarkable success, as to have 
already allowed its able director to deduce results of considerable interest in meteor- 
ology. Among these are results, which observations made merely at stated hours 
would probably never have disclosed*. Attention has been called by Mr. Johnson 
to a remarkable serration in the temperature curves during the day. This serration 
is found only when there is a considerable amount of solar radiation; it disappears 
during sunless and cloudy weather. While it is explained by referring it to the in- 
fluence of the solar heat upon the ground, and the consequent circulation of small 
atmospheric currents, it affords a very satisfactory confirmation of the trustworthi- 
ness of the photographical method of registration. 
The following Table presents a specimen of the observations made on May 11 
with two thermometers, one of which (a) had its bulb plunged 0:25 inch below the 
open mouth of a bell-glass, and the other (0) was freely suspended in the air. 
May 1l. 
Time. (a). Diff. | Fluctuation. || (4). Diff. | Fluctuation. 
hm ° ° 4a HO ° ° 
252 | 662 | +0°8 62°6 | +1°2 
253 | 67:0 | +0-2 } +16 || 63:3 | +0°7 } +2°4 
254 | 67:2 | +0°6 645 | 40:5 
S65 | 67-8. | —o:1 —o1 || 650 | —o-2 —0°2 
256 | 67-7 | +0°3 64:3 | +0:2 
257 | 680 | +01 ; 65:0 | +0°5 | , 
258 | 68:4 0-0 +05 | 65-5 | +071 & ate 
259 | 684 | +01 65:6 | +0-4 
30 | 685 | —0'5 -—o5 || 660 | —o-6 —0'6 
3 1 | 68:0 | +0°2 +02 || 654 | +01 +0°1 
32 | 68-2 00 65:5 | —O1 } ms 
3.3 68°2 —0°9 } 249% 65°4 —0°6 qa 
Ba) 67-3. |, —O-1 64:3 | +0-2 +0°2 
35 | 67-2 65:0 
On plunging the bulb of (a) more deeply, the amplitude of its fluctuations pro- 
gressively diminished, and they ceased almost entirely when the bulb was 14 inches 
below the edge of the bell-glass. 
* See Report of the British Association for 1855, Trans. Sect. p. 40. See also Intro- 
duction to the Meteorological Observations made at the Radcliffe Observatory in the year 
1857, p. xxxiv. 
