SCIENTIFIC SUMMARY. 
195 
shells, above which was blown sand, which was washed down by the rain 
over the clay, and deposited in ledges formed by the projecting beds of shale, 
while the siliceous particles of which the sand was composed were cemented 
together, partly by carbonate of lime held in solution by the rain water, and 
derived from the shells occurring in the sand and in the clay, and partly 
from a ferruginous cementing material contained in the latter. A hard 
sandstone was being formed, not unlike one of much older date, in some 
places enclosing one or two recent shells, thus making the resemblance more 
complete. 
A new Cycadean fruit has been described by Mr. W. Carruthers, who has 
given it the name of Beania, in honour of Mr. Bean, the successful explorer 
of the fossiliferous beds of the Yorkshire Oolites. Mr. Carruthers’ attention 
was drawn to the specimen (in the Bean collection) in the British Museum 
by Mr. Henry Woodward. It is from Phillip s “ Upper Shale ” at Scar- 
borough. It is not associated with any Cycadean remains on the small slab 
on which it occurs, so that there is no indication to which of the several 
leaf species it belongs. A small fragment, however, of Acrostichites Wil- 
liamsonis occurs on the slab. — Vide Geological Magazine, March. 
MECHANICAL SCIENCE. 
Concrete Arch , — A remarkable experiment in the use of concrete has 
been made on the Metropolitan District Railway. Over one of the cuttings 
an arch of concrete has been constructed, of 75 feet span, 7^ feet rise, and 
12 feet width, resting on concrete skewbacks. The thickness of the arch at 
the crown is 31 feet and the thrust on a section through the crown due to 
the weight of the structure alone is 7 tons 17 cwt. per square foot. When 
complete, rails were laid over the arch and a train of seven trucks, weighing 
49 tons, with a wheel base of 57 feet, was run over the bridge. Ballast 
weighing 170 tons was then spread over the arch and the train again re- 
peatedly run over the bridge. The maximum average thrust at the crown 
during the experiments reached the high value of 15 tons 2 cwt. per square 
foot. The arch showed no signs of failure or distress. The concrete con- 
sisted of gravel and Portland cement in the proportion of 6 to 1, and was 
laid in mass on close boarding set upon the centering. 
Centrifugal Governor . — Sir W. Thomson has designed a centrifugal 
governor, in which the increase of centrifugal force due to increase of speed 
produces the regulating action without change of radius. The centrifugal 
force is made the normal pressure for a frictional arrangement simply and 
directly resisting the rotary motion. In an instrument exhibited at the In- 
stitute of Engineers in Scotland, the weight of the revolving masses and the 
power of the springs by which they are controlled was so adjusted as to 
require an increase of one foot-pound per second in the driving power for an 
increase of one per cent, in the speed above the desired amount. 
Suez Canal. — Mr. Fowler, C.E., has recently published in the Times a 
careful report on the present condition and prospects of the Suez Canal, 
which is very favourable as to its success from an engineering point of view 
