Back on this date in 1935, Congress authorized the Social Security Act and appropriated slightly less than $25 million for its first year of operation. (来源：英语学习门户 http://www.EnglishCN.com)

Seventy-one years later, the Social Security appropriation is in the billions, not millions, and the government program is still alive, if not necessarily well. Its position as the so-called "third rail" of politics has survived yet another challenge. Today we look at both the literal and the figurative third rails.

The literal third rail refers to the metal rail through which electric current is led to the motors of an electric vehicle, such as a subway car. Touching this third rail is dangerous, if not lethal. That sense of danger was borrowed into the allusive sense of third rail, used for a charged political issue that threatens to prove deadly to anyone trying to touch it.

The literal third rail first appeared in print in 1888. The earliest figurative application of third rail to the issue of Social Security we could find dates back to 1981, credited to House Speaker Tip O'Neill, a liberal Democrat who advised Republicans not to touch that issue.

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