My introduction to a tesseract
was during an episode of Carl Sagan's "Cosmos" series in the 1980s, where he was demonstrating how beings of dimension N would perceive
items of dimension N+1. The tesseract, Sagan explained,
is a 3-dimensional projection of 4-dimension hypercube. Watch the embedded video for more information.

The Tesseract website, which has nothing to do with a hypercube
as far as I can tell, deals in some very cool antique scientific instruments. I learned of it from an article in
Astronomy magazine where an editor recommended it when
researching the potential value of a collectible telescope. Run by Drs. David and Yola Coffeen, Tesseract has a huge inventory
of items representing, among others, Astronomy
, Microscopy,
Navigation,
Drafting,
Demonstration & Experimentation,
and Calculation.

"We are always interested in buying single items or collections. In addition to buying and selling early instruments,
we can perform formal appraisals of your single instruments or whole collections, whether to determine fair market value
for donation, for insurance, for loss, etc. We were recently engaged to appraise a major medical collection of several hundred
items being donated to an American museum, and to appraise a major European collection of early scientific instruments,
being insured for a loan exhibition."

The first item that caught my attention were the "Napier" Rods, in the
Calculation list. Having heard of them
but having no idea how they worked, I turned to Wikipedia.
Invented by Scottish scientist John Napier, they
are a mathematical multiplication aid that have markings such that the two numbers for which the product is sought are constructed
by laying the corresponding 'rods' side-by-side, and then the answer is obtained by adding the numbers residing in common
diagonal paths. It sounds complicated bu it really quite simple in practice. As with using a slide rule, the user needs
to keep track of decimal points during calculation. You can take possession of this fine artifact for a mere $9,500. The
Calculation category also includes many varieties of slide rules (not just for mathematics), sectors, scales, and other
types of calculators.

The Demonstration & Experimentation category has some of the coolest-looking contraptions and gizmos.
Many you have probably seen in the background of paintings of famous scientists, mathematicians, astronomers, et al. Shown
to the right is a set of early 19th century official French standard weights that are fractions of a kilogram, for $3,800.
On the left is a "Gyroscope Compendium" set of gadgets used to demonstrate physics principles. If you own one, it might
be worth $4,500 according to the Tesseract folks.

An interesting "Gear of Planets" is found in the
Astronomy list. Although its exact date
of construction is unknown, it obviously dates after Copernicus came up with the heliocentric planetary system (1543), but before
Pluto was discovered by Clyde Tombaugh (1930) - although
since Pluto was demoted to not-a-real-planet status by the International Astronomical Union in 2006, its omission from the
contraption might mean it was actually made after 2006 (just kidding). Since the circular gear for each planet is driven
by a common long spur gear, the orbital periods are synchronously proportional to the radii of each circle (circumference
= 2π • radius). I didn't take time to measure
and estimate the accuracy of the model. It can be a conversation piece for your display case for $950.

Tip: One of the best ways to view a website's collection of images without having to click through a lot of individual
pages is to do a Google image
search using the site:etesseract.com format in the search box.

Posted on April 28, 2016

A huge collection of my 'Factoids' can be accessed from my 'Kirt's Cogitations'
table of contents.

Topical Smorgasbord, another manifestation of Factoids,
are be found on these pages: