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When it's finished, what its designer hopes will qualify as the world's tallest barometer will begin measuring the atmospheric pressure in the glass atrium of Portland State University's Engineering Building.
Tom Bennett, an instrument technician at PSU's Maseeh College of Engineering & Computer Science, came up with the idea two years ago.
"When the Science II building was remodeled, they took out all the glass pipes that were used in the chemistry lab," Bennett said. "The 2-inch diameter, 10-foot long pipes were just sitting and available. I asked myself, 'What can you do with long pieces of thick glass pipe?'"
The answer was, let's make a barometer. A really tall one.
There was plenty of space in the Engineering Building's soaring atrium, and the barometer went up last week alongside the 102-foot Dryden Drop Tower, which is used to teach students about "gravity, displacement, velocity, acceleration, and aerodynamic drag as well as a wide range of gravity-masked phenomena."
A glass tube filled with mercury was long the standard, but because of mercury's toxic properties most of today's barometers are digital; they can also use water.
When Bolle and wife moved to Australia in 1999, the barometer went with them. It was eventually moved to a visitor center in the town Denmark, Australia, in 1999. A dispute led Bolle to dismantle the barometer in 2011.
Although it was impressive and worked, Bennett saw a problem: Bolle measured the total frame height of his barometer, not just the height of the fluid column, which is a tad under 33 feet. Bennett knew he could build a bigger, better barometer.
In short (or if you prefer tall), the Maseeh College Barometer's fluid column is 40.6 feet tall and the frame is 46.5 feet tall, which would easily make it the tallest barometer on the planet.
Bennett has a bone to pick with Bolle's design, as well.
"He ignored the technique used by the first water barometer made in 1820 in England by the physicist John Frederic Daniell, who used a few inches of mineral oil floating on the water to prevent water evaporation," he said. "Since the Bert Bolle barometer just uses water, the water evaporates when the vacuum pump is turned on and this results in pump problems."
After receiving city permits to build it, the barometer's aluminum triangular truss that supports the pipe went up last week, and the glass pipe sections were slipped inside and completed last Tuesday. Testing on the glass pipe connections was done Friday, and Bennett hopes to add the oil Monday. A green LED light will illuminate the column of oil and the reservoir at the base.
"The special thing about it is that it's so big and can measure minute pressure differences," said PSU engineering professor Franz Rad. "One of the things we emphasize is not only for students to do measurements in the lab, but how to design experiments. The whole idea was that students would be involved in designing the tower, installing the bolts and lateral bracing – it was a real hands-on experiment."
Bennett said three grad students – Austin Hudson, Hank Chiu, and Zdenek Zumr – were, no pun intended, instrumental in getting the barometer from the drawing board to the atrium.
And just how sensitive will that tallest barometer in the world be?
"I'm kind of expecting that when someone opens the door here that we'll see a little blip because of the pressure change forcing air in or out of the building," Bennett said.