240 Mr Joseph J. Murphy on Revolving Storms. 
general motion of the lower strata of the atmosphere in the 
middle latitudes. These changes have not been satisfac- 
torily accounted for. Perhaps they are due to the fact that 
in tropical latitudes the general direction of the upper and 
lower air-currents is usually very different, while in higher 
latitudes it is usually nearly identical; in the former the 
cyclone, extending from the lower into the upper current, 
is as it were compressed between them: when it gets into 
the latter, being no longer thus compressed, it expands by 
its own centrifugal force, loses force by expansion, and 
drifts in the general motion of the air. Its motion, how- 
ever, is more Pole-ward than this, and is perhaps a resultant 
of the general motion of the air, and a remaining westward 
tendency of the cyclone, due to the cause already explained. 
Description of a Plant-house at Rockville, Blackrock, near 
Dublin. By Mr James Brew ey.* 
My fern-house is a triple-span roof standing north and 
south, 60 feet wide—7z.e., three spans of 20 feet each; the 
length is 48 feet; the height of the sides to the spring of 
the roof is 13 feet 6 inches—of this, 7 feet is a wall; in — 
the lower part are ventilators near the ground, which are 
opened and shut from the outside; the rest of the sides is 
glazed with fine ribbed glass. I think it is called Hartley’s 
rough plating. The centre span is supported by three 
pulars, 12 feet apart from centre to centre. These pillars 
are rough brown slate, square, about 3 feet each way. The 
stones are laid horizontally, with ample spaces between, 
from the mortar being picked out for plants. From pillar 
to pillar are Gothic arches of the same material, covered 
with ferns, lycopods, &c. Thus there are two rows of four 
arches each. Hach side has in addition a row of eight 
arches of 6 feet each, planted in the same manner, each roof 
rises about 7 feet; so the highest part of the house is 21 
feet. The north end is a wall, against which is a mass of 
* Communicated by Mr N. B. Ward to the British Association Meeting at 
Newcastle-on -‘Tyne, August 1863. 
