28 REPORT—1843. 
385. But even were some methods of scraping possible, it only temporarily 
removes the evil, leaving its cause untouched ; and that this cause is in such 
rapid operation, at least in some localities, as to be a most serious evil, may 
be illustrated by the following observations :— 
Stevenson, in his account of the Bell Rock Lighthouse, mentions that the 
bottom of the temporary light-ship, after being newly caulked and pitched, 
was found covered over with mussels (Mytili) three and a half inches long, in 
three years and seven months from the time she was moored off the Bell Rock. 
It is stated in the Transactions of the Wernerian Society, vol. ii. p. 243, 
that the spawn of the Cirrhipoda class of fouling animals became developed 
upon a feather, on which it lay before the latter had decayed in sea water, 
and that they will cover a ship’s bottom in a few months. 
These observations applied to wooden vessels, and the prevalent opinion 
seems to be, that iron ships “foul” even more rapidly than these do in similar 
circumstances. 
386. The opinion that iron vessels as well as railway bars receive some 
hidden power of resisting corrosion when in use which they lose at other 
times, has been before alluded to. 
387. The origin of this view with respect to rails is obscure. Wood, in 
his ‘Treatise upon Railways,’ quotes a Report of Mr. G. Stephenson, in 
which the following passage occurs :— 
“One phenomenon in the difference of the tendency to rust between 
wrought iron laid down as rails, and subjected to continual motion by the pass- 
age of the carriages over them, and bars of the same material either standing 
upright, or laid down without being used at all, is very extraordinary. 
“« A railway bar of wrought iron laid carelessly upon the ground alongside 
of one in the railway in use, shows the effect of rusting in a very distinct man- 
ner ; the former will be continually throwing off scales of oxidated iron, while 
the latter is scarcely at all affected.” 
388. This is the first notice J have found of this opinion, which has since 
been repeated in various quarters, but no fact, that I am aware of, has been 
given to support the view which a mere casual inspection of rails so situated 
suggests. 
When rails lying parallel on the same line of way, but one set in and the 
other out of use, are examined, appearances do undoubtedly seem to support 
the opinion. The unused rails are found covered with red rust, often coming 
off in scales parallel to the surface, while those in use present a light brown 
or buffish coat of rust, without any loose scales. I am much disposed how- 
ever to believe that there is no real difference in the amount of corrosion in 
the two cases, and that the difference in appearance arises partly from a de- 
ceptio visus, by the effect of the bright and polished upper face of the used 
rail (kept so by constant traffic) contrasted with the rusty face of the unused 
rail, and partly from the fact, that as fast as rust is formed upon the rail in 
use, it is shaken off by the vibration of passing trainsyand blown away by the 
draft of wind which accompanies their motion, and that the rail is soiled 
and partially blackened by coke and other dust, &c. 
Recently the assumed difference in rate of corrosion has received a new 
version ; it has been stated that rails in use do corrode as well as those out 
of use, provided the traffic pass over them in both, that is in opposite direc- 
tions as on a single line of way, but do not corrode if the traffic be confined 
to one direction. These results have been attributed to some undescribed 
and occult magnetic action. 
389. Whether either or any of these views be correct or not I am unable 
at present to say, but as the subject is not only interesting in a scientific 
