106 REPORT—1849. 
chimneys, accelerate corrosion; still the difference is so remarkable, as to 
induce the suspicion, that there are some forces engaged which more or less 
retard the corrosion of iron when exposed in railway bars, in every condition, 
z,¢. whether travelled over or not. Thus in one year, the losses by corrosion 
on one square foot of surface of the following sorts of iron exposed in the 
City of Dublin, were— grs. avoir. 
2. Common Shropshire bar ...........00+.--+ 151416 
3. Best Staffordshire bar .........000005 05005 “1OLS04 
4, Best Dowlais Welsh bar ........ Weteistoatt <a - 990°:00 
5. Low Moor boiler plate ............02.2.++- 98240 
8. Faggoted scrap bar .............- ooleva tiated 622'80 
We now return to detail the examination made of the rails when just 
removed from the Kingstown Railway, as to their magnetic condition after 
the first exposure thereon, and also after their exposure upon the Dalkey line. 
For this purpose the railway bars were brought into an open piece of level 
ground, remote from any masses of iron or other causes of magnetic disturb- 
ance; and at some considerable distance from where they lay, a triangle and 
purchase-blocks were so arranged, that any one bar could be suspended by 
the middle of its length in a horizontal position; the length of the bar being 
preserved either in the magnetic meridian or at right angles to it, or could 
be tilted up vertically, or in the line of the dip. 
Each bar was first placed horizontally in the magnetic meridian by a line 
parallel therewith, previously marked out on the ground by two distant ob- 
jects. A Kater’s compass of delicate adjustment was now brought to rest, 
and then advanced slowly parallel with the bar towards the end facing the 
magnetic north, and the action of the bar on the needle noted. The compass 
was then brought back to the southern face or end of the bar, and the action 
also noted. The bar was then turned horizontally end for end, and similar 
experiments made ; and lastly, the bar being turned round 90°, and thus being 
at right angles to the magnetic meridian, similar trials were made for each 
end. By this means the induced polarity by terrestrial magnetism was made 
evident, and separated from the idio-polarity, or the magnetism permanently 
proper to the bar. 
Lastly, each bar was examined as to the position of the neutral point or 
points betwixt the poles, by carrying the compass slowly along its length 
while the bar was at right angles to the magnetic meridian, and observing 
when the needle was neither deflected to the east nor to the west, but con- 
tinued to point to the magnetic north station mark, the point opposite to 
which was the neutral one. With a longer needle of greater delicacy, and 
suspended within a glass cylinder from silk fibres, examination was made as 
to the state of polarity of each bar, with reference to the depth of the rail, 
the top edge while in use being always uppermost and the bar horizontal. 
These experiments were made for every bar; it will not be necessary to 
describe the individual results in detail, but give them generally. 
The set No. 1, not travelled over, and exposed to corrosion alone.—W hen 
examined after exposure on the Kingstown line, they showed strong polarity 
by terrestrial induction, but very slight idio-polarity. Some of the bars, 
however, when placed in the magnetic meridian, showed a feeble permanent 
polarity, reverse to that of Fig. 7. 
the earth, 7. e. to induction, a 
and more than one neutral : ‘ 
. s N,S 
point; one bar, for exam- $ M4 NS 
C woo SO - 2 Sets eS 
ple, showed three neutral a te 6  peiaadaa 
points at a, b and ec, and 
hence had eight poles with reference to length. 


