Notice regarding Railways. 391 
which it is procured by decomposition ; whereas, in the case of 
oil-gas, it is well known that its illuminating power is rather di- 
minished, than augmented, by its change of condition ; the light 
which it emits, in the gaseous state, being somewhat less than 
that of the oil itself, when it is consumed in an Argand lamp, 
according to the ordinary mode. Lastly, the residue of the 
coal, after the latter has been used for the purpose of producing 
gas, is still valuable as an article of fuel ; while that of the oil is 
good for nothing, but to clog with an useless product the vessels 
in which the decomposition is effected. 
Aiit. XXII . — Notice regarding Malleable Iron Railways. 
No subject, in Mechanical Philosophy, is at present more 
interesting than that of Railways, and we had expected to have 
been able, in the present Number, to lay before our readers a 
short view of their construction and operation, and of the gene- 
ral principles and comparative advantages of this mode of con- 
veyance over that of Canal Navigation, so far as they can be de- 
duced from the facts and observations already known, as well as 
to point out where additional information and experiment is yet 
wanting, to complete the theory of this important branch of me- 
chanics. We must now, however, defer this to another oppor- 
tunity. Meantime, we recommend to the attention of our read- 
ers the perusal of the printed correspondence, on the merits of 
malleable iron and cast-iron rails, published by Mr Birkinshaw, 
at Newcastle. The patent malleable iron-rails are thus described 
in the article Railways, in the Supplement to the Encyclopaedia 
Britannica. 
An improvement has lately been made in the construction of 
the malleable iron-rails, which promises to be of essential utili- 
ty. It consists in the use of bars, not rectangular, but of a 
wedge form, or swelled out on the upper-edge. In the -rectan- 
gular bar, there is evidently a v/aste of metal on the under sur- 
face, which, not requiring to be of the same thickness as where 
the waggon-wheel is to roll, may be evidently reduced with ad- 
vantage, if it can be done easily. The bar may then be made 
deeper and broader at the top than before, so as with the samo 
c c ^ 
