# Compascope(d)

 Noon LMST

Background
Description
Operation
Photos
Manual
Patents

Related
References
Compascope

## Background

I've been looking for one of these for a number of decades.  It's part of my interest in the relationship of position and time, i.e. Navigation and my interest in Sundials.  These were used on Jeeps in the North African desert during W.W.II.  It probably was used in other places where a magnetic compass does not work, for example near the magnetic poles of the Earth.  Note that a magnetic compass does not work well on vehicles made of ferrous metal such as ships, jeeps, tanks, etc.  A Gyroscopic compass is an expensive solution.

In the "History of [the] U.S. Army Topographic Laboratories (1920 to 1973)" the sun compass is mentioned (pg 73) as project number 8-34-05-004 Compass, Sun, Universal.
also on pdf pg 175 (d) Universal Sun Compass good for all latitudes, not just 0 to +/- 45 deg.  Prototypes made by Brunson Inst Co.  Has square from factor, i.e. not the SC-1.

## Description

The theory of operation is that you know the date and local mean time and approximate location on Earth.  This device then knows the azimuth to the Sun and so works as a compass.  Note that the bearings are relative to true North, not magnetic bearings.

The heart of this instrument is based on the Analemmatic sundial (Wiki)  where a central plumb post casts a shadow and that line intersects the hour markings.  But here it's the intersection of the hour line and the latitude line that's important since this is a universal dial, meaning it can be used anywhere on the Earth including both the Northern and Southern hemispheres.  Unlike the common Analemmatic sundial this one has the correction for the Equation of Time (Wiki) built into the Date Bar.

## Operation

### Time Input

One of the inputs needed is the Local Mean Solar Time.  Mean Time is what we use everyday.

Solar time differs from mean time by the Equation of Time (Wiki).  This is shown as a graph on some Sundials and has a value between about +15 minutes and -15 minutes depending on the date.

Local time differs from standard time by an amount that depends on how far your longitude is from the longitude of the meridian for your time zone.  It also depends on whether or not Daylight Savings Time (Wiki) is being observed.
There's an Android app on the Google Play Store called Solar Time that makes the above corrections.

 When LMST is 12:00:00 (Noon) the Sun is exactly South. Note the corrections being made: phone Time:             3:47:35 Equation of Time:          2:19 Longitude Correction:   -:12:39 Daylight Saving:        -:60:00 LMST:                   3:47:35 PS I have cropped out the ad at the bottom of the screen on the free version of Solar Time. PPS The phone Lon: -123.1640186 is different from my actual Lon:-123.164023x   The difference amounts to less than 2 feet, so the very big city name error is a problem with their map lookup. The corrections are fixed for each date, so for the outdoor test they are: EoT: +2:28 Long Corr: -12:39 DST: -60:00 Will take photo at Noon LMST. The Sun Compass is just sitting on a concrete paving stone and not at all stable.  So the bubble level is not solidly centered.  More accurate results if well anchored.

During W.W.II the vehicle driver would have a watch that was reasonably accurate and probably set to Zulu or GMT time.

## Photos

 Fig 1 The box was probably made using green wood.  Over the last 75 years the wood has dried out and shrunk causing the split in the top cover. Fig 2 Fig 3 Fig 4 Fig 5 Preparation for Noon LMST The iron in Sun Compass was pulling magnetic compass. Fig 6 photo @ Noon LMST Note 26 April set on date scale. Whole unit turned and leveled so North at LMST. Fig 7 photo @ 1:00 PM LMST I have marked in white 1:00 LMST & 39+ deg N. I'm a little above 39N  Note date close to 26 Apr. Fig 8 photo @ 2:00 LMST Fig 9 photo @ 3:00 LMST Fig 10 Top to bottom: Protractor Plate on Gimbal mounting with bubble level vial Solar Plate Date Bar Fig 11 Solar Plate LMST hours around edge North Latitude at top, South Latitude at bottom Fig 12 Date Bar with Equation of Time Fig 13 Shadow bar can be pre-positioned at the intersection of LMST and latitude

## Patents

X9428 Solar Compass, W.A. Burt, 25 Feb. 1836 - after patent office fire, so only drawing.  Also see: reconstruction. -

2441636 Sun compass, Joseph M S Kaufman, Krasnow Shelley, 1943-07-06 - Kaufman also invented the Type MC-1 Pocket Card Compass with electromagnetic-dampening
 Fig 3, 82: Glass capsule containing radioactive luminous material

2366228 Optical instrument, Abrams Talbert, Milford B Moore, William S Karr, 1942-12-30 - viewer for stereo aerial photographs
2573130 Electrical timer, Milford B Moore, Ellsworth D Willis, Robert L Ginther, 1944-10-27 - Intervalometer (Wiki) for aerial cameras or bomb release
2868924 Time base mechanism, John E Hewitt, Louis F Schmidt, David G Gardner, Abrams Instr Corp, 1956-06-26 - intervalometer
2944169 Motor and governor supporting assembly, Louis F Schmidt, Abrams Instr Corp, 1956-07-05 - Louis F Schmidt: small light weight motor governor combination for aircraft
4018532 Sun direction detection system, Fletcher James, Louis F. Schmidt, George D. Pace, Jr., 1975-09-24 - Louis F Schmidt worked on this and other NASA sensors

4899451
Solar compass and time indicator device, Jean-Pierre Dandurand, 1988-04-11 -
Solar compass, Felix G. Steele, 1994-06-03 -
Direction indicator, Barry S. Waltho, 1992-09-10 -

### Goerz sun compass

Fig 17 in The Sundial Goes to War shows this device that has some similarity to aircraft gun sights (Mk 18, Mk 20).

J. M. Boykow, the inventor of the Goez sun compass has a number of patents.

1703386 Bomb Sight, Johann Boykow, Firm Of Optische Anstalt C P G, Filed: 1921-08-23, Pub: 1929-02-26

This was intended to be a bomb sight for horizontal bombing, but precision horizontal bombing with iron (dumb) bombs has never worked and I think never will.

2039878 Apparatus for finding the course along any definite great circle, Johann Maria Boykow, 1936-05-05 - Goerz sun compass

# Compascope

There were a few identical instruction sheets for the Compascope in the Abrams Sun Compass box.  So I got one.
Maybe there's some reason for that?

The short tube is a flashlight that uses a 222 lamp and AA battery.
When looking through the sight you see the compass rose at the bottom of the image.  This is accomplished by using a mirror (Fig 3).  This is commonly done is hand held levels.
There are no lenses, i.e. there is air all the way through the top part of the tube, also common in hand levels.

 Fig 1 Fig 2 Fig 3  You can see the mirror and the tip of the 222 flashlight lamp.

1214150 Aerotransit - similar device.

## Related

Astro-Compass MkII
Chinese Compass & Sundial
Gyroscopes
North - Finding it
Optics
Sundials

## References

The Sundial Goes to War Malcolm Barnfield - article from the British Sundial Society - An excellent overview of many Sun Compasses!
Sundial mailing list
A Key to the Solar Compass, and Surveyor's Companion by W.A. Burt, 1881, 225 pgs - free on line
Abrams Sun Compass -
Compass Museum -
Cole Universal Sun Compass - on line applet that prints Sun Compass card for your Latitude. Not working for me.
Cole Sun Compass - small photos and info
Royal Museums Greenwich - Cole Universal Sun compass MK 3 -