The key advantage of the four-rail system is that neither running rail carries any current. This scheme was introduced because of the problems of return currents, intended to be carried by the earthed (grounded) running rail, flowing through the iron tunnel linings instead. This can cause electrolytic damage and even arcing if the tunnel segments are not electrically bonded together. The problem was exacerbated because the return current also had a tendency to flow through nearby iron pipes forming the water and gas mains. Some of these, particularly Victorian mains that predated London's underground railways, were not constructed to carry currents and had no adequate electrical bonding between pipe segments. The four-rail system solves the problem. Although the supply has an artificially created earth point, this connection is derived by using resistors which ensures that stray earth currents are kept to manageable levels. Power-only rails can be mounted on strongly insulating ceramic chairs to minimise current leak, but this is not possible for running rails which have to be seated on stronger metal chairs to carry the weight of trains. However, elastomeric rubber pads placed between the rails and chairs can now solve part of the problem by insulating the running rails from the current return should there be a leakage through the running rails.
How did return current effect water and gas in iron pipes?
water and gas mains

Notably, the most broadly influential innovation of 20th-century American tort law was the rule of strict liability for defective products, which originated with judicial glosses on the law of warranty. In 1963, Roger J. Traynor of the Supreme Court of California threw away legal fictions based on warranties and imposed strict liability for defective products as a matter of public policy in the landmark case of Greenman v. Yuba Power Products. The American Law Institute subsequently adopted a slightly different version of the Greenman rule in Section 402A of the Restatement (Second) of Torts, which was published in 1964 and was very influential throughout the United States. Outside the U.S., the rule was adopted by the European Economic Community in the Product Liability Directive of July 1985 by Australia in July 1992 and by Japan in June 1994.
Who was at the forefront of the fight to change the laws on defective products?
Roger J. Traynor

The world's largest deposit of natural bitumen, known as the Athabasca oil sands is located in the McMurray Formation of Northern Alberta. This formation is from the early Cretaceous, and is composed of numerous lenses of oil-bearing sand with up to 20% oil. Isotopic studies attribute the oil deposits to be about 110 million years old. Two smaller but still very large formations occur in the Peace River oil sands and the Cold Lake oil sands, to the west and southeast of the Athabasca oil sands, respectively. Of the Alberta bitumen deposits, only parts of the Athabasca oil sands are shallow enough to be suitable for surface mining. The other 80% has to be produced by oil wells using enhanced oil recovery techniques like steam-assisted gravity drainage.
Where are the Athabasca oil sands located?
Northern Alberta