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55
cient reflection can only be obtained from a Welsbach burner when the opal sides of the shade subtend
an angle of about 90 deg. The opal upper portion of the "Reflex," 2¾ in. vertical is shaped on this
plan and, consequently, the shadow beneath the burner is less than with any of the other shades. The
lower part of the shade, 2¾ in. perpendicular, is of clear glass so that two-thirds or more of the incandescent
mantle is directly exposed to the teacher's eyes ; the effect being intolerably dazzling. For this reason
the " Reflex " is quite unfitted for the classroom. This effect is easily remedied by extending the sides
of the " Reflex " with a simple paper shade figured as the 90 deg. shade globe.
The relative values of these shades from the point of efficient lighting can be shewn by the figures
from the following experiment in which the metre candle value of the illumination was measured on
the desks immediately below the
burner and then at intervals of a yard along the horizontal desk tops, which were five feet vertically
below the burner. All the shades were examined in this way. The results found for the " Squat,"
" Calypso," and " New No. 3 " were alike, and 1 m.c. less than the " Reflex," below the burner: they
are therefore omitted from the table. The experiments were made consecutively with the same burner
and mantle.

The improvement on the unreflected light by the use of the " Reflex " shade is great, but the
results to be obtained by increasing the depth of the shade are most striking. The gain is obtained by
reflecting the rays that would otherwise be dissipated upon the upper part of the walls of the room, and
the teacher's eyes are screened from the dazzling of the naked mantle by the depth of the shade. The
general wall illumination of the room does not suffer; it is quite as good as when the " Squat " is used,