Great improvements were also made in the hoisting apparatus and cages used to extract ore and transport the miners to their work. As the depth of the diggings increased, the hemp ropes used to haul ore to the surface became impractical, as their self-weight became a significant fraction of their tensile strength (breaking weight). After hemp rope, iron chains began to become more common. However, fracture was quick, at around half a millisecond. In 1829 Wilhelm Albert had studied and reported on the failure of the iron chains and began creating a twisted metal cabling known as Albert Rope. In 1864 Andrew Smith Hallidie manufactured wire rope and was heavily involved in building early cable bridges and ropeway conveyors; his wire rope went on to be used in San Francisco's famous cable cars, and was also added to the cable drums in the hoist houses on the Comstock Lode. Another innovation, were spring loaded cages. The only way in and out of a shaft mine, was in the cage, cabled to the hoist.