even if this building is so far either to the right or left from the
point directly opposite as one-half the width of the street. It frequently
happens that the window lenses can be tilted, as in the figure, in the plane
of the plate so that the window plates can be used in place of canopies.
It would be impossible without unduly increasing the size of this book to
give sufficient information upon this subject to enable persons not
skilled in Lucical Engineering to determine when this can be done to
advantage, and what to insert. It is always safe to use canopies in these
places, and this is what is recommended. However, if there is any reason
why canopies cannot be used, before giving up the proposition entirely, it
is best to call an engineer skilled in the subject.
TABLE OF LUXFER PRISM AREAS EXPLAINED.
Before using the table of Prism Areas it is
necessary to find the ZENITH-TANGENT, pages
187-188, and
the PRESCRIPTION, pages
189-197, as explained above, pages
81-83.
The tables on pages
198-235 show the areas of
prism plates required to light interiors under various conditions. Any
two pages which are in view when the book is open treat all variations
of a room of one width. Four classes of illumination have been set down.
The first is for occupants who need a very brilliant light such as
bookkeepers, dealers in dry goods, clothing, etc. This illumination has
been designated "For Desk Work." A second illumination has been provided
for those who need a very good light, such as occupants dealing is
jewelry, men's furnishings, shoes, books, millinery, etc. This has been
designated "For Fine Merchandise." A third illumination has been provided
for those requiring a good light for ordinary purposes, such as occupants
dealing in hardware, rubber goods, groceries, furniture, etc. This has
been designated "For General Merchandise." A fourth illumination has been
set down for those requiring still less light, and has been designated
"For Storage." Having turned to the pages corresponding to the room
width and having selected the table
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