: ON RAILWAY BAR CORROSION. 93 
Hence the average gross weight of each train is=29°8 tons, or nearly 30 
tons. 
And the remarkable fact appears, that the wseless load per train is to the 
useful as 25°44 : 4°36, or as 5°83 : 1, or nearly as 6:1; and that the abra- 
sion or destruction of rail relatively to the useless and useful load are in the 
same ratio. “ 
Qnd. We deduce from this, that the absolute corrosion of a length of rail 
out of use to that of the same rail in use, or exposed to traffic, is in round 
numbers about, as 15°30 to 6°26, or that the difference in favour of the latter 
is 9°04; but it will be best to postpone a minute comparison of the rate of 
corrosion until we have the results of the further experiments also before us. 
While these experiments were in progress, it seemed very desirable to me 
to obtain a set of experiments made co-ordinately with the above, but upon 
a single line of railway where the traffic would be in both directions, viz. 
backward and forward over the same set of rails; as from views suggested 
by Mr. Nasmyth, it was possible this might be an important element in the 
question. Mr. Nasmyth’s views, which are briefly alluded to in my Third 
Report on the Corrosion of Iron, will be found more particularly detailed by 
himself in the following interesting letter to me, which I have his permission 
to publish :-— 
“ Bridgewater Foundry, Patricroft, 
May 19, 1842. 
“ My pear Sir,—On my return from the continent I had the pleasure to 
receive your valued letter respecting the rusting and non-rusting of railway 
rails. I have not had any opportunity to obtain the exact comparative rate 
of oxidation under the two conditions, but so strikingly different is the oxida- 
tion of the one, as compared with the other, that a very slight glance will 
satisfy any one that they are under very marked and different influences, in- 
asmuch as, in the case of the Liverpool and Manchester, the rails of which 
have been laid and exposed to all the changes of wet and dry for upwards of 
five years, there is no more appearance of rust than merely a light-brown 
coating of mud-coloured water, more the result of the splashing of rain; 
while in the case of the London and Blackwall Railway, in which the car- 
riages travel alternately east and west on the same rail, the rusting is proceeding 
at that rate, that although they have not been laid two years, cakes of rust are 
falling from the sides of the rail, and the ground for 12 inches on each side 
of the rail is yellow with rust. This may be said to be mere ocular demon- 
stration, but to any one willing to be convinced, it is most satisfactory proof. 
I should be most glad to have my observations and theory on the subject 
brought to the most severe test; but to do this would not be very easy, as 
¥ . ef us . . . . 
5 to time and similar circumstances, all but the one in question, viz. the one 
way travelling versus the both ways alternately ; for to be a true experiment, 
we should have both bars of the same iron in the same place, only one 
travelled on in one direction, the other in both, and an equal amount of 
travel on each. The experiment required in that form might be tried by 
mechanical contrivance, bwt then we know not as yet what is due to the cor- 
rection with so vast a length of rail as in the case of railroad; but in the 
absence of any very delicate and ‘scientific-like’ results I am fain to con- 
| _ tent myself with the most striking difference, which is observed, or may be 
observed, by any one whose attention is directed to the subject. I may also 
mention, that on the Liverpool and Manchester line, all the sidings, as they 
are called, i.e. those parts of the rail which serve for backing trains into 
when it is desired to permit others to pass them on the same line,—that all 

