We Help You Pass
Our free online study guide really works. You can study for your FAA private pilot ground school exam right now. For more info about the 4VFR.COM project, click here. You can find a daily update log here.
Live ATC Audio Streams
Tune into live air traffic control frequencies from North America. This feature requires Real player. Start listening to ATC now!
Reference Library
Our glossary lists and databases have grown quickly. I am working to create an on-line reference library to tie together all the loose ends. You can check out what is currently available in the library
FAA Practice Exam - New!
Introducing our newly enhanced practice exam. Now with figures!. Take a test a day for a week, and I guarantee you will do better on your exam. Get Started Now!
Show your support for 4VFR.COM - Link us. Bookmark us. Tell your mother about us. Press CTRL-D to bookmark this site now!. Check out one of our proposed T-Shirt Designs.
Feature Article: It's About Time
A sailing ship's speed over a nautical a mile was, historically,
measured by means of a knotted (knots) rope tied to a log. A
sand filled timing glass would be used to measure the time from
leaving the log dead (much as a dead man might appear) in the
water (dead reckoning) and the number of evenly spaced knots
passed along the rope. All of this would be recorded in the logbook.
Since the chronometer was yet to be invented, sailors had no
way to determine longitude except by this dead reckoning. Within
crude limits, speed and compass indications could be used to
determine estimated distance and estimated longitude. Magellan
in 1519 had access to charts, globe, theodolites, quadrants,
compasses, magnetic needles, hourglasses, and timepieces. He
was unable to determine exact longitude.
An 18th Century a chronometer (weighed over 36 pounds) was
first used to get longitude. A chronometer differs from a clock
or watch because it has a temperature adjustment for greater
accuracy. Captain Cook in 1768 had three different clocks for
his voyage. In 1779 he sailed with 4 chronometers and a nautical
almanac which enabled him to determine longitude.
The very first effort to make a calculator was financed by
the British to make the making of the nautical almanac easier.
The effort was stopped when the mechanical calculator was only
a year from being completed. The original design was completed
in 1991 and found to work accurately. Interesting to speculate
where the world would be had it been completed in the 1700s.
The complete story of the chronometers and the
failure of the British to follow up with a 'computer' is in a
small book "Longitude" now available as a pocket book.
30 years ago I knew a pharmacist who spent his evenings at
an all-night pharmacy working out prime numbers on rolls of butcher
paper with a pencil. Did we miss a 300-year head start on computers
by so little?
_______________________________________________________________________
Revolutions per minute - rpm First counted by paddle wheel ship
captains._____________________
Last Modified December 7, ©2019 TAGE.COM
