If a room is divided longitudinally into two
parts, by a row of columns, by a glass partition, by screens, by
decorations, or by anything of this kind, it is evident that these
obstructions or decorations cut off from one part of the store a large
portion of the light which would otherwise be uniformly diffused. In
such cases the tables must not be applied to the full width of the
store, but must be applied to the several independent parts thus
Example 9.--A room 20 feet wide, 60 feet long,
13 feet high, having light walls, to be used "For General Merchandise,"
is to be lighted from one end, and having a line of columns through the
center of the store, faces a street 50 feet wide, opposite building 40
feet high. Required the area and kind of prisms.
Solution.--Our problem is the same as No. 1,
with the exception of the row of columns. For a room 10 feet wide, 60
feet long we need 32 square feet of
M prisms, so that in this
case we shall need 64 square feet of
M and J prisms.