424, Prof. Hennessy on the Vertical Currents 
were intended to be merely provisional, I did not make them at 
specific fixed hours, but at such times as presented disturbances in 
the atmosphere, or which afforded sufficient leisure for continued 
attention. A journal was kept, from which I make the following 
extracts. Before doing so, it is proper to remark that by the term 
“vertical currents” in these extracts, as well as in the title of this 
paper, I do not mean currents actually perpendicular to the 
horizon, but rather oblique currents with an upward or down- 
ward tendency. 
“ June 28, 7 a.m.—Air perfectly still, flanges horizontal, head 
of vane towards the east. 7.30 a.m.—Breeze with slight 
vertical currents until after 8. The currents were upward from 
the ground. The flanges were often perfectly horizontal, and 
their mean angle of inclination was small. About 10 a.m., a few 
fine scattered clouds (cirro-cumuli) were observed to move in a 
direction contrary to the wind as cbserved near the earth. 
“From 8 p.m. to 3.45.—Wind extremely gentle from E.S.E. 
Upward current, angle of inclination estimated at about 5°. 
The upward currents often continued for several minutes to- 
gether. The angle was sometimes almost imperceptible. The 
sky became gradually overcast towards evening. 
“June 30,10 a.m.—Sky completely overcast, strong wind from 
E.S.E., rapid oscillations of the dise during the greater part of 
the day. About 6 P.m., the wind blew in violent gusts from the 
east, and the dise showed alternations of upward and downward 
currents with occasional short intervals. These observations 
led me to conclude that rapid currents of air cannot generally 
advance with the same steadiness as currents of water; the greater 
mobility and elasticity of the former fluid probably allow its 
movements to easily acquire a species of undulation. Thus we may 
account for the motions of the branches of trees, which generally 
swing backwards and forwards, showing rapid variations in the in- 
tensity of the wind. During breezes composed of a succession of 
strong sudden gusts, it was difficult to estimate the inclination 
of the flanges, as each fresh impulse drove the flange beyond the 
angle due to the pressure, and before it had been sufficiently long 
oscillating about its true position to allow a correct observation, a 
fresh gust would perhaps drive it in a different direction. 
“July 1,9 a.m.—Wind N.E., strong breeze with vertical cur- 
rents. The position of the flanges was sometimes steady for 
many minutes, with a very small inclination; upward currents 
appeared to predominate in duration. 
“July 2, before 9 a.m.—Air still and warm, head of vane di- 
rected to S.E. After 9 a gentle breeze from E. and E.S.E., 
with an upward tendency. The disc remained steady at a small 
angle, sometimes for two minutes together. Towards noon the 
