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used which is quite simple and portable. Wingen's photometer has been used for several years in London
schools. It consists of a metal box, 8 in. by 6.5 in. by 4 in., within which, near one end, is placed a
benzine lamp, the wick of which can be raised or lowered at pleasure. Outside the box is a small shelf
covered with a white card upon which falls the rays of light to be examined. Inside the box is a similar
white card lighted by the benzine lamp. The two white cards are viewed simultaneously at the bottom
of a tube glazed with red glass, whilst the wick of the benzine lamp is adjusted till the cards appear
equally brilliant. The value of the illumination is read off by looking through a small slit in the side
of the box, a mark on the glass covering this slit is taken as a " backsight," the top of the flame as a
" foresight," and the figure on the scale fixed on the side of the box beyond the flame, in a line with the
" back " and " fore " sights gives the value of the illumination in " metre-candles." That is a light
equal to that which would be given by so many standard candles at a distance of one metre from the
spot, where the examination is being made. This instrument was carefully examined by Mr.
Harman and tested by himself and by the expert in charge of one of the L.C.C. gas testing stations,
against the standard pentane lamp used there. It was found to be correct for the purposes required, and
the calibration, which extends from 10 to 50 metre candles, was further extended down to 1 metre candle.
Minimum Desk Illumination. The possibility of distinguishing one object from another
by sight depends primarily on the illumination of the objects. A finger mark on a sheet of white paper
is easily recognisable in good daylight, but not easy of recognition by candle light. The same principle
holds good for distinguishing print on paper. The possibility of distinguishing any given object depends
upon the familiarity of the examiner with the object examined. A normal sighted person of middle age
will distinguish characters on paper in a poor light with greater readiness than a small child, because
the characters are more familiar to the adult, and so much more easily recognised. Conversely a child
requires a better light to learn to read than does an adult to whom reading is second nature. From a
large number of experiments the least illumination permissible on the school desk of a child has been
found to be equal to 10 m.c. This may seem a large amount of light if ten wax candles fixed in a
chandelier and their effect in a room is considered, but it is not large when compared with ordinary
daylight in a fairly lighted room. To-day is cloudy, the sky dull, and there is not a ray of sunshine,
but the light on the paper is equal to 60 m.c., and the desk is fourteen feet from the window, and even
at a distance of twenty-four feet the illumination is equal to 30 m.c. So that 10 m.c. is a modest demand
for the minimum illumination on each desk in a schoolroom.
Variety of Illuminants. Gas and electricity were the only illuminants used in this
enquiry, and then only as used in rooms of moderate dimensions. Most of the Council schools are
lighted by gas, burned directly as an illuminant at the jets of fishtail or batswing burners, or used as a
source of heat to render Welsbach mantles incandescent. The use of naked gas jets is still the rule
especially in the non-provided schools, but the Welsbach fittings are supplanting them rapidly with
excellent results. The value of naked gas jets as a direct illuminant as compared with the superior
value of the use of the same or a less quantity of gas with the Welsbach mantle cannot better be shown
than by giving the result of the comparative examination of one room fitted with these two varieties of
burners.
A convenient infant classroom hung with four points of gas was fitted first with the most approved
form of naked gas burner, Bray's No. 4 with No. 6 regulator, that is a good pattern well-made fishtail
burner of No. 4 size with another No. 6 size slipped over it. The effect of this double burner is to reduce
excessive gas pressure or " flaring " and give a steady flat flame of high illuminating power. The
desk lighting was then examined. Then these burners were replaced by Welsbach " C" burners and
mantles with " Calypso " shades. Although the gas consamed with the Welsbach burners was no
greater, perhaps less than that burned by the fishtail burners, the desk illumination was increased nearly
threefold over the whole room. With the naked gas jets the minimal desk illumination was obtained
over only a very small part of the room. The desk area A, B, C, D of the room is 179 square feet and
the patch of fair illumination 26 square feet, and this only when no obstruction such as the bodies and
hands of the children come between the lights and the desks.
On the other hand, with the Welsbach the illumination never falls below 10 m.c.,whilst in most
parts of the room there is an ample margin for the interference which bodies or hands will make with