320 NOTICES OF THE MEETINGS [May 20, 
illuminating effect obtained from animal and mineral bodies is pri- 
marily derived from the vegetable kingdom; every plant being an 
apparatus for the absorption and concentration of light and heat 
from the solar rays, and for the retention of these forces during its 
passage through the subsequent stages in the formation of vege- 
table fuel. 
Until the commencement of the present century artificial light 
was derived almost exclusively from the animal kingdom; but the 
great economy attending its immediate production from our vast 
stores of vegetable fuel is becoming more and more apparent, and 
is in fact so generally admitted, as to render more than a mere 
allusion to it and a glance at the following Table, unnecessary. 
TapLE — shewing the comparative cost of light from various 
sources each equal to 20 sperm candles burning 120 grains per 
hour each, for 10 hours. 
d. 
Wax - : - - 22 
Spermaceti - . - 8 
Tallow - - - 8 
Sperm Oil (Carcel’s Lamp) - 
London Gases, B, C, D, E* - 
Manchester Gas - - 
London Gas, A. - - 
cCoOornan”? 
— 
oO 
We will therefore confine our attention principally to the light 
produced from vegetable fuel, in considering the economical and 
sanatory bearings of artificial light. 
The production of artificial light depends upon the fact, that at cer- 
tain high temperatures all matter becomes luminous. The higher the 
temperature the greater is the intensity of the light emitted. The 
heat required to render matter luminous in its three states of 
aggregation differs greatly. Thus, solids are sometimes luminous 
at comparatively low temperatures, as phosphorus and phosphoric 
acids. (A jet of flame produced by the formation of these substances 
was exhibited, and its temperature shewn to be quite inadequate to 
the ignition or even scorching of the finest cambric or gun cotton.) 
Usually, however, solids require a temperature of 600° or 700° F. to 
render them luminous in the dark, and must be heated to 1000° 
F. before their luminosity becomes visible in daylight. Liquids 
require about the same temperature. But to render gases luminous, 
they must be exposed to an immensely higher temperature ; even the 
intense heat generated by the oxy-hydrogen blowpipe scarcely suffices 
to render the aqueous vapour produced visibly luminous, although 
* London Gases, A, B, C, D, E—These are the gases furnished to consu- 
mers by five of the principal London Companies. For obvious reasons the 
names of the Companies are not mentioned. 
