90 ; REPORT—1849. 
Total surface in contact with the wheels=1°5 in. x 36=54: sq. in. per lineal 
yard of rail. 
Total surface in contact with filling pieces beneath, and hence partially 
protected from corrosion, is==1*7 in. xX 36=61'2 sq. in. per lineal yard. 
Besides this there is the surface covered by the chairs and wedges, which 
partially but very slightly prevent corrosion, water finding its way between 
in wet weather very readily. There is one chair at every three feet, which 
covers about twenty-four square inches, including the wood wedge. The 
meeting-chairs at every fifteen feet cover twice this. 
The top surfaces of the rails which are run upon appear to corrode 
searcely at all, owing to the fine polish preserved by the rolling of the wheels ; 
if it be assumed that neither this top surface corrodes nor the bottom surface 
covered with the filling slip, then 
The total surface per yard lineal exposed to corrosion is=414 sq. ins.— — 
(54-+61:2)=298'8 sq. ins. and the uncorroded surface=(54+61°2) _ 
=115'2 sq. ins.=2:08 sq. ft., or the corroded is to the non-corroded 
surface per yard, as 298°8 : 115°2, or as 2°59: 1; 
omitting any account of the surfaces covered by chairs, which are common 
to all the three sets, and do not prevent the corrosion materially beneath. 
But if the top or running surface of the rail be supposed to corrode equally — 3 
with the sides, then 
The total surface per yard exposed to corrosion is=414 sq. ins.—61°2 
=352'8 sq. ins., and the corroded is to the uncorroded surface per 
yard as 352°8 :61°2, or as 5°76: 1. 
The set No. 1, not travelled over, corrodes on the top as well as sides, and ; 
hence exposes to corrosion per lineal yard, 414—61°2=352°'8 sq. ins. 
The weighings of the three sets of railway bars took place for the first ex- 
periment on 24th of March 1841: they were previously marked, as mentioned — 
above, (°), (**), ("**), with a centre punch near one end on the side of the — 
bar, and each bar of each set numbered from | to 6. 
The weighings of the coal-tarred set were of course made before the ap- — 
plication of the varnish, in applying which care was taken not to heat the bars 
so as to scale them or to abrade, or in any way alter their weights. 
The weighings were made under my own eye, by David James, an intel- 
ligent workman, with a beam about six feet long, sensible when loaded with 
one rail to about 2 ounces avoirdupois, or ;1,;th of the load in one scale, or _ 
stscth of the whole load. Four accurately adjusted half-hundred weights of — 
cast-iron, varnished over, prepared from the brass standard were used, and — 

retained for use again on subsequent removal of the rails, and the other 
weights were accurate brass standard avoirdupois weights of my laboratory. 
Each rail was weighed separately, and the weights were checked by myself. 
The following table gives the data and numerical results of the first series 
of experiments. 
All three sets, No. 1, No. 2 and No. 3, were laid down, and the traffic of — 
the second day of July 1841 was the first that went over them. 
They were all taken up again and reweighed on the 30th of April 1842, 
being exposed to corrosion and traffic for an interval of 303 days. 

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