A
screwdriver is a
tool that uses the priniciples of
simple machines (in this case, the
Wheel and Axle) to enable one to apply enough
torque to a
screw to enable you to rotate it despite significant
friction.
The Phillips screwdriver was invented by Henry Phillips, in Portland, Oregon in the early 1930s. He was looking for a screw that could be turned with more torque than a flat-head screw without slipping, while still being turnable with automated equipment. His solution was to used a cross-slotted head instead of the single slot of usual screws. He patented his invention on 1 July 1936, and was assigned patent number 2,046,343 for the screw head and 2,046,838 for the screwdriver. Researchers wanting more information may also want to look at US Patents 2,046,837 and 2,046,840 for other information.
His design was not well accepted at first. A competing design, the Robertson Screwdriver, used a square socket that could be fastened faster and tighter. But the auto industry preferred the Phillips design precisely because of these shortcomings -- The automated screwdrivers on factory lines popped out of the screw's recesses more easily, thus preventing over-torquing. Cadillac was the first to began using these screws in 1936.
By 1949, the Philips Screwdriver had become so common, that Henry was stripped of his patent. Henry himself died in 1958 at the age of 68.
The Philips screwdriver is enough of a story to earn an chapter in Witold Rybczynski's "One Good Turn: A Natural History of the Screwdriver and the Screw" You can also find a reference in Laura Lee's "The Name's Familiar", though the dates in her writeup are horribly wrong. Finally, the dates are more reasonable in About.com's writeup on the phillips screwdriver, entitled "Fasteners from Hell?". As always, the Delphion patent database is also very useful.
Thanks to Gritchka, who made me chase down the truth about the dates and times. My quick research said that the screwdriver was patented in 1938, then stripped in 1919. Furthermore, Henry Phillips apparently died in both 1958 and 1988 at the age of 68. Kinda scary how typos can become facts!