- In mathematics, the Riemann hypothesis is the conjecture that the Riemann zeta function has its zeros only at the negative even integers and complex numbers with real part 1/2. Many consider it to be the most important unsolved problem in pure mathematics. It is of great interest in number theory because it implies results about the distribution of prime numbers. It was proposed by Bernhard Riemann (1859), after whom it is named.
- Snoqualmie Falls (waterfallsnorthwest.com)
Snoqualmie Falls is among the largest and most significant waterfalls in the United States. Situated along the Snoqualmie River in the town of Snoqualmie, the falls plunge a into a huge amphitheater carved in ancient volcanic bedrock. Officially Snoqualmie Falls has a height of 268 feet, however lidar data suggests this measurement to be that of the hydroelectric system, rather than the falls itself, and that the waterfall itself is about 10-12 feet shorter. The natural volume of the Snoqualmie River, coupled with the great height of the falls makes it one of the most powerful waterfalls in North America. However, that power was too tempting a prospect for intrepid engineers, and in July of 1899 the Snoqualmie Falls Hydroelectric plant went online - the first hydroelectric facility in the world to be built entirely underground. In 1910 a second powerhouse (this one above ground) was constructed downstream of the falls, which was greatly expanded again in the late 1950s.