illuminating agent, we have to take into consideration the extreme
smallness of the point from which the light radiates in the electric
arc. A light having the power of many thousand candles will expose but
a fraction of the surface for heat radiation which is shown by one
gas-jet, and, as I have endeavored to explain, these rays contain very
much less of the heating principle than those from gas or other
artificial light.

The purity of electric light has another important aspect, which can
scarcely be overestimated--namely, the facility with which all the
most delicate shades of color can be distinguished. I understand from
persons better skilled than myself in such matters that this can be
done almost as readily by electric as by day light, and I have little
doubt that the slight difference in this respect will entirely
disappear when people become somewhat more familiar with the different
conditions--the effect of such shades viewed by electric light being
more like that with comparatively feeble direct sunlight than the
subdued daylight usually prevailing in stores and warehouses.

Again, it has frequently been urged that persons working by electric
light have thus induced inflammation of the eyes. No doubt this is so
with light containing the highly refrangible rays in excess; but it is
difficult to see how such an effect can occur with light composed as
is the light with which the eyes are constructed to operate in perfect
harmony.

As you are aware, there are other methods of obtaining light by
electric energy, and in order to make a fair comparison of one which
has lately attracted a great deal of attention and capital, I will
relate to you the result of observations made during a recent visit to