401 
wires. A three-inch wire rope ought to have pulleys and 
drums ten or twelve feet in diameter, and the thicker the rope 
is, the larger ought the pulley and drum to be. 
I conceive that an upcast shaft may be more prejudicial to 
metallic ropes than a downcast ; not only on account of the 
sulphurous and other corrosive vapours that are constantly 
ascending it. but because of the unequal temperature to which 
the metal is subjected, the ropes being for the most part hung 
in the hot shaft during the day, and coiled upon the drum in 
the open air during the night. This alternate exposure to 
heat and cold, occasioning alternate expansion and contraction 
of the wires, may probably, in course of time, operate injuri- 
ously on the rope itself. 
The failings of the metallic ropes (more especially of those 
made by Smith) may perhaps be attributed to faults in the 
manufacture, and not in the principle. May not the wires of 
which the rope is composed have been unevenly stretched by 
the maker ? and if so, they have not, when put in operation, 
undergone an equal degree of tension. 
In spite of the varnish and tarry matter which have been 
applied to the wire rope to preserve it from oxidation, the 
metal has nevertheless been considerably corroded in the 
course of a few weeks. This corrosion is more injurious to 
the small wires than it is to the thicker ones, from which I 
should infer that a rope made of thick wires will be more 
lasting than a rope made of small ones. 
An effectual anti-corrosive pigment, for coating the exterior 
of the wires and strands, would be extremely valuable in the 
manufacture of these ropes, and it can scarcely be doubted 
that the resources of chemical science will, ere long, supply 
this desideratum. 
p 2 
