13 
Ordinary Meeting, October 31st, 1882. 
H. E. Roscoe, Ph.D., LL.D., F.R.S., &c., President, in 
the Chair. 
“ Belted Skew Pulleys,” by Archibald Sandeman, M. A. 
With that plane at right angles to the axis of a pulley 
which halves the face named the Plane of the Pulley, 
and with the locus of the centre of the cross section of 
a belt named the Midline of the Belt; the only thing 
needed for either of two pulleys to drive the other by 
means of a closed belt looping them in tightly together 
(art. 184 of Willis’s Mechanism) is 
That the Midline of the belt leave each pulley in 
the plane of the other. 
The planes of the pulleys may be taken vertical and 
therefore the axes horizontal. By so doing the belt is no^ 
drawn away by its own weight, and the axes are the more 
easily set up and steadied. 
If the axes be parallel to one another the planes of the 
pulleys must be one and the same. Else the belt’s midline 
would leave either pulley, not in, but on one side of, the 
other, and therefore run off this other toward that side. Thus 
with condirectionate or contradirectionate axes the midline 
of the belt lies wholly in the one plane of the pulleys. This 
is the simplest and commonest case of a pair of pulleys with 
open or crossed belt. 
Call two straight lines Skew when they are not in one 
plane. And call two pulleys Skew when their axes are 
skew. 
Proceedings— Lit. & Phil. Soc.— Vol, XXII,— No. 2.— Session 1882-3. 
