Pelroteum : its Sources and UseSt. 
3?7 
as good a light, and are sensibly cheaper than gas, having besides 
the advantage of being capable of arrangement without reference to 
the situation of the gas mains. The oil lamps, however, though 
very good and efficient, are by no means perfect, for they are apt to 
go out occasionally, especially in stormy weather. This I attribute 
partly to the somewhat defective make, quality having been sacrificed 
to cheapness ; but there is undoubtedly room for invention, or at 
least considerable improvement, in the construction of out-door lamps 
intended for burning heavy mineral oils. 
In lighthouses petroleum has now become the standard illumi- 
nant. Cautiously and step by step, as became the introduction of a 
substance in some of its forms not free from danger, it has gained 
ground ; and it has now established itself as next in value to 
electricity, as a perfectly safe, trustworthy, and economical illumi- 
nant. The lamps are all constructed on the principle of Argand, 
and have concentric wicks rising to as many as ten in number, the 
oil being maintained at a constant level between 2 and 3 inches 
below the flame. So perfectly adapted to the oil are the structure 
and material of the wick, and the adjusting mechanism, that a lamp 
will burn some 500 hours comsecutively without trimming. The 
unassisted candle-power of these lamps ranges from 20 to 2,215. 
As a source of power, petroleum is rapidly gaining ground, 
especially where motors of moderate size are needed. The records 
of the Royal Agricultural Society show that, for many years past, 
efforts have been made to produce petroleum engines, but never, 
until quite recently, with any practical success ; chiefly, I think, 
because oils of low flashing point, or petroleum spirit, were used. 
The dangerous nature of these would alone have condemned any 
engine, however efficient for general use ; save, indeed, in the form 
advocated by Mr. Yarrow, in which petroleum spirit acts only as 
the working substance or agent for the conversion of heat into work, 
and is therefore not expended, except by way of leakage, so that the 
difficulty of supply does not arise. It was not till the Show at 
Nottingham * * in 1888 that Messrs. Priestman brought out their 
engine working with heavy oil having a high flashing temperature. 
That engine was tested by Lord Kelvin and by myself independently, 
and gave an efficiency of one brake horse-power to l‘731b. of oil. 
At the next year’s Show (Windsor, 1889) the consumption fell to 
1‘42 lb. ; at the next (Plymouth, 1890) to 1 ’243 lb. ; and Professor 
Unwin this year reports ^ that a brake horse-power has been ob- 
tained by the combustion of 0 946 lb. It is proved by experience 
that these engines do not need any special attendants : neither 
boiler nor chimney is required ; the fuel is much more cleanly ; and 
the engine can be got to work in a few minutes. It is certain, there- 
fore, that they will increase greatly in favour with the public, 
and will prove formidable competitors to gas engines. Naturally 
also, Messrs. Priestman’s success has stimulated the inventive spirit. 
' Journal of the Royal Agricultural Society, Vol. XXV., s. s., 1889. 
* Vroccciings of the Institution of Civil Engineers, Vol. CIX., 1892. 
