74 
On Artificial Light . [February, 
A further disadvantage is the quantity of heat generated 
by the use of gas as an illuminant. I will admit that there 
are in our climate very few weeks in the year in which heat, 
per se, can be regarded as a nuisance. But heat, like light, 
may be produced and applied in the wrong place. If we 
consider the tendency of heated air to rise upwards, we shall 
see that the sources of heat should be placed as low as 
possible. In a room lighted with gas this arrangement is 
reversed. Up aloft is, so to speak, a stagnant lake of hot 
air in which the heads of the inmates are plunged, and are 
further heated by radiation from the ceiling and the upper 
parts of the walls. At the bottom the air is cold. I have 
observed a difference of g° F. between the temperatures of 
such a room near the ceiling and near the floor respectively, 
and I have reason to believe that there are cases where a 
much greater difference would be registered. If there is 
any trust to be put in the old maxim, to keep the feet warm 
and the head cool, this is a condition the very reverse of 
salutary, and experience fully confirms the Supposition. 
I know it is contended that, for equal amounts of light, 
the heat generated by oils, tallow, stearine, wax, paraffin, 
&c., is greater than that thrown off by gas. This is true, 
but not to the purpose. The heat coming from lamps and 
candles is developed at a lower point in the room, so that 
there is a less extreme difference between the ceiling-tem- 
perature and the floor-temperature. Again, as I have 
already mentioned with reference to the question of cost 
where oils or tallow are used, a less quantity of light is 
demanded. 
Another defect of gas is so well known that we may feel 
surprise at the little attention which it practically receives. 
Gas is poisonous if inhaled even very largely diluted with 
air ; and such mixtures, further, according to their propor- 
tions, are more or less powerfully explosive. Hence in 
premises lighted with gas there is always a certain margin 
of danger which does not exist where candles or non-volatile 
oils are used to give light. A slight defeCt in the work of 
the plumber or of the manufacturer of gas-fittings, — neither 
of whom is immaculate, — or a casual oversight on the part 
of a child or a servant, may lead to a serious calamity. 
Even if a man can guarantee the utter absence of careless- 
ness within his own doors, or if he eschews gas-lighting 
altogether, he is still at the mercy of accidents as long as it 
is used by his neighbours or by the local authorities. Many 
of my readers will remember the explosion which began in 
Charlotte Street, Fitzroy Square, and which extended — 
