199 
and closed by water-tight sliding-doors. Engines, central pad- 
~ dle-wheel, refreshment rooms, &c. between lines of rail. Dia- 
meter of wheel 14 metres. Height of deck 6 metres. Weight 
of vessel 1200 tons; weight of engines (of 500-horse-power) 
+ weight of coal and stores 200, + weight of train of twenty 
carriages 200 tons. ‘Total, 2100 tons. Advantages—great 
speed, no oscillation, Tubes in compartments, and supplied 
with pumping apparatus connected with engine. 
The PRESIDENT indicated a simple method of drawing an 
ellipse which he was in the habit of using himself. 
On the Aurora Borealis.. By Jamus Stuart, M.A. 
Tromty. 
There are several different kinds of Auroras, arches, bands, 
converging lines, general. luminousness of the sky, &e. In some 
instances the convergence of the bands is due to perspective. 
The year of maximum aurora occurs every ten years, and at the 
same time as that of maximum sun spots, and of maximum per- 
turbations of magnetism. Auroras in the northern and southern 
hemispheres are frequently simultaneous. Before an Aurora in 
the northern hemisphere and during the first part of the dis- 
play the magnetic needle is deflected te the west; during the 
Aurora it makes frequent and viclent excursions and then is 
deflected toward the east. In the southern hemisphere it is 
deflected also but in exactly the opposite way. This may be 
accounted for by currents running in the earth from the Poles 
to the Equator. De la Rue supposed these to be caused by 
electricity conveyed upwards at the Equator by evaporation, 
and thence to the Poles by the winds in the upper air, whence 
it was discharged into the earth at the Poles. The difficulty of 
such a thing is the nonconducting nature of the air. If a cloud 
of some interplanetary dust or medium of some kind were to 
come near the earth, the lower parts of this getting mingled with 
