1866.] Our Coal Supply and our Prosperity. 473 
appears at present to be unlimited, and to present new sources year by 
year, will become a most important agent both for lighting and as 
a motive power. “ But,” says Mr. Jevons, “what is petrolewm but 
the essence of coal, distilled from it by terrestrial or artificial heat ?” * 
Here, again, the clever author of the work which has excited so 
much uneasiness is significantly brief, and what little he does say 
is hardly correct. Neither he nor any one else is justified in 
affirming that “its natural supply is far more limited and uncertain 
than coal,” for it is only just discovered, and the supply in America 
and elsewhere appears to be almost unlimited. As to its artificial 
production, he says it can only be had by the distillation of “ some 
kind of coal;” but what kind of coal is used for the purpose? 
Could the shale from which it is at present extracted at home be 
employed for any other purpose? and how much is so produced ? 
These are questions which Mr. Jevons should have considered. 
Moreover, if he recollected that petroleum is the “ essence of 
coal,” and that it is so dear as 15/. per ton, why does he forget 
that the freight from America upon an article worth 15/. per ton, 
as compared with that upon 1/. (which will probably be the price 
of native coal at the American outports before many years), com- 
pletely annihilates the carrying distance between the two continents ? 
And should petroleum come into use for engines, as well as for 
lighting (which recent experiments here and in the States render 
more than probable), the great difficulty in the way of the import- 
ation of our fuel at once disappears, and we shall have good cause 
to rejoice in the fact that an important source of our light and heat 
will be the same as that of our food, and that we shall be less 
dependent upon the resources of our little island. ‘To show our 
readers that we are not merely theorizing, and that it is only a 
question of mechanical application, and consequently of the exercise 
of the inventive faculty, which will place other easily-obtainzble 
substances above coal or coal-gas as illuminating and force-giving 
agencies, we will just transfer to our pages two. or three facts 
from the recent address of Dr. Letheby to the British Association 
of Gas Managers.t First, as to heating power :— 
Whilst Cannel gas raises 1,950 Ibs. water 1° Fah. 
Common gas will raise 2,786 lbs. Be 
Paraffin (petroleum) will raise 3,619 Ibs. me 
Tallow will raise 5,054 lbs. . 
Now, as regards lighting power : 
When a magnesium wire the 100th part of an inch in diameter 
is doubled and twisted, it burns at the rate of 2°4 grains per 
minute, and gives the light of about 69 standard sperm candles ; 
* «Coal Question,’ p. 141.” 
+ ‘Chemical News,’ June 15, June 22, July 6, 1866. 
