ectually replace gas for lighting purposes. They both
did the lighting, but they utterly failed to keep the currents of air
steady. I have always remarked draughts whenever I have remained any
length of time in rooms where the electric light is used. On a warm
evening the electric light and candles would undoubtedly have kept the
room cooler than gas, with the same kind of ventilation; I do not think
they would have put an end to cold draughts. This the steam from the gas
does in all fairly built rooms.

It is a well-known fact that dry air parts with its relatively small
amount of specific heat, in an almost incredibly rapid manner, to
anything against which it impinges. Steam, on the contrary, from its
great specific heat, remains in a heated state for a much longer time
than air. It is not so suddenly reduced to a low temperature, and in
parting with its own heat it communicates a considerable amount of
warmth to those bodies with which it comes in contact. Thus the products
of the combustion of gas (which are principally steam) serve a useful
purpose in lighting, by keeping at the ceiling level a certain stratum
of heated vapor, which holds up, as it were, the carbonic acid and
exhalation from the lungs given off by those using the room. The obvious
inference, therefore, is that if we take off these products from the
level of the ceiling, we shall take off at the same time the impure and
vitiated air. On the other hand, if we make use of a system of
artificial lighting, which does not produce any steam, then we shall
have to adopt means to keep the air at the ceiling level warm, in order
to prevent the heated impure air from descending in comparatively rapid
currents, after having parted with its heat to the ceiling. It may very
frequently be observed on chilly days that a number of currents of cold
air seem to travel about our rooms, although there may be no crevices in
the doors and windows sufficient to account for them; and, further, that
these currents of cold air are not noticed when the curtains are drawn
and the gas is lighted. The reason is that there is generally not enough
heat at the ceiling level in a room unlighted with gas to keep these
currents steady. Hence the complaints of chilliness which we constantly
hear when electric lights are used for the illumination of public
buildings. For example, at the annual dinner of the Institution of Civil
Engineers, held at the end of April last in the Conservator