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a system of twelve lines leads at once to the remaining 15 lines; — 
viz. we have a line ¢,,, the intersection of the planes which 
contain the pairs of lines (q@,, b,) and (a,, b,) respectively. 
The model is formed of plaster, and is contained within a 
cube, the edge of which is=18-2 inches; the lines a, b, ¢ are 
coloured blue, yellow, and red respectively; the lines a,, 0,, 6, 
being at right angles to each other, in such wise that taking 
the origin at the centre of the cube, the axes parallel to the 
edges thereof, and the unit of length = 1°6 inches, the equations 
of these three lines are 
y=0, z=-1. 
The model is a solid figure bounded by portions of the faces 
of the cube, and by a portion of the cubic surface, being a 
surface with three apertures, the collocation of which is not 
easily explained. 
(2) On the Tides in a rotating Globe covered by a Sea 
of constant depth at all points in the same latitude, 
and attracted by a Moon always in the plane of the 
equator, supposed either fixed or moving with uni- 
form angular velocity; considered with reference to 
the tides as they are in nature, and the retardation 
of the earth’s angular motion. 
(3) Also, On the motion of imperfect fluid in a hollow 
sphere rotating about its centre under the action of 
impressed eaternal periodic forces, considered with 
reference to the phenomena of Precession and Nu- 
tation. By Mr Rours. 
In the first of these papers it was shewn that by assuming the 
Moon to be in the equator always, her effect would be greater 
