Originally Posted by KevinJS

Richard PMed me the answer. That is exactly what it does. Any idea what it is called?

Sent from my iPad 4 HD mini

How about a map wheel.

Sort of, but there is a specific name.

What do you use to take measurements such as speed, or mileage? That will give the last 5 letters of the name - the class of instrument.

Sent from my iPad 1 using iPF - Greetings

Originally Posted by Richard Brown

Sort of, but there is a specific name.

What do you use to take measurements such as speed, or mileage? That will give the last 5 letters of the name - the class of instrument.

Sent from my iPad 1 using iPF - Greetings

You do realize that the original challenge didn't ask for the exact name of the instrument,don't you.

Richard Brown said:

"OK, I was hoping to answer a challenge before posting. The challenges have proved well. Very challenging!

Here's mine.

What is this part of?

What is it used for?

As a bonus, but not an essential question, how is it used?







The original image is definitely out of copyright.

Sent from my iPad 1 using iPF - Greetings"

Fair enough, Scifan. You have the challenge now. The instrument is called an opisometer.

Sent from my iPad 1 using iPF - Greetings

Need to reattach the pic scifan. I can't read it.
AA

Originally Posted by Richard Brown

Fair enough, Scifan. You have the challenge now. The instrument is called an opisometer.

Sent from my iPad 1 using iPF - Greetings

I've looked and I discovered that the terms map wheel,map meter and opisometer are used interchangeably for the same device.

Here's one for everyone.
What are we looking at?What was it used for?Who is credited with the invention of the first of these devices?



What is the cone shaped piece in the second photo and what is it's purpose?

Here's another photo.

It looks like the mechanism for an early marine chronometer. These chronometers had to be certified, for accuracy, and were used for naval navigation. Knowing the exact time is crucial for determining longitude in when navigating using a sextant in celestial navigation. It was the invention, a lifetime of work, by John Harrison that allowed an era of exploration and navigation to begin.

I'm less sure of the first, since I haven't found any good sources. The cone shaped pice is called the 'schnecke' in German, which translates to 'snail'. I've no idea if that is what it's actually called in English.

In the diagram I saw there is a chain that wraps around the snail and the geared drum (shown in the last picture). Both the gear and the snail are a continuous spiral (thus the snail) rather than distinct rings. My guess is that it is used to compensate for variable strength (torque) of the spring as it unwinds.

File:L-Cronometer.png - Wikipedia, the free encyclopedia


Note: I'm out of the house for a bit, maybe an hour. Be back soon to see if I need to post a challenge.

You've solved the mystery.The photos are of an antique Marine Chronometer.
The chronometer in the pictures is about 120 years old,but virtually identical Chronometers are still made today,mainly for the collectors market.
The "cone" shaped piece is called the Fusee.
Here are more pictures.
An excellent resource to read is "The Marine Chronometer" by Rupert Gould,who restored the Harrison Chronometers,H-1 to H-4.
There is an excellent TV miniseries about the problem of finding longitude at sea.It's called"longitude".














The hands are made of gold and the end stones of the balance wheel are diamond.
Your turn to post the next challenge.