A desire to return to the West Indies, where I cruised as an apprentice on board the U.S.S. Hartford in 1903 and 1904, prompted my first thought of celestial navigation.
Anchored in Shamrock Cove, a part of Corpus Christi Bay, about the middle of November, 1930, the conversation of our week-end party turned to planning a 3-week voyage on the seagoing ketch Siesta. As the other three members of the party knew I had served an apprenticeship in the Navy, they concluded I should be the navigator.
Well, right then I had to disappoint them by informing them that my knowledge of navigation would not carry us out of sight of land.
The owner of the Siesta would not be stopped, so it was agreed that night we would secure the necessary equipment and try to master the art without the aid of an instructor. But after a number of home study lessons, we reached the conclusion that it would require a competent instructor if we were to become efficient navigators and everything was put away for the time being.
During the following spring I visited Chicago and attended two demonstrations and lectures at Adler’s Planetarium. It was here I first grasped the principle of nautical astronomy. However, I had no thought of attempting to plan and design an instrument until about three months later.
While waiting for the other members of my family to dress, I had unconsciously made a tube out of the magazine I had been reading. Glancing down, I noticed the light spot on my coat from the electric light and this thought flashed in my mind: The angle of the rolled magazine in my hand is the angle of the light ray as cast on my coat! That was the thought which has turned out to be the idea of finding your position on this earth by the observation of a given celestial body, by means of an instrument which I call a “position finder.”
Right here I would like to say, I have talked to those in charge of two planetariums and many navigators and demonstrated the latest instrument, and they all remarked, “Why didn’t some one think of that idea before? It is so simple.”
The instrument measures at one observation the vertical angle, the azimuth, and the hour angle of a celestial body, indicated by the ray of light from the body, and mechanically solves the astronomical triangle. In all of the demonstrations I have made in this country and in Europe, the results as to accuracy and the speed with which it is done have always surprised those witnessing the demonstration. It is my opinion that the comfortable position the observer assumes while making observations, sitting down and focusing his eyes on one spot, is the reason for the accuracy obtained with this instrument.
The instrument in reality reproduces the movements of the universe and might be considered a miniature celestial sphere; it consists principally of a horizon plane, declination, latitude and altitude arcs, and hour angle circle. The horizon plane carries the altitude arc, azimuth circle, and a level bubble. All arcs are graduated in degrees and carry a tangent micrometer screw reading to minutes.
In the center of the horizon plane is a 1/8-in. diameter circle which is the geometrical center of the instrument and corresponds to the observer’s position on the earth when making an observation on a celestial body. The graduated azimuth circle rotates inside of the horizon circle which, when the instrument is properly set, gives the azimuth of any heavenly body sighted.
The declination arc is graduated in degrees and pivoted at the north and south poles of the instrument frame; thus, when the declination of the observed body is set on the declination arc, the motion of the body across the heavens can be followed by rotating this arc. By reading the hour angle circle, which indicates the angular position, from the meridian the exact longitude can be determined. The exact latitude of the place of observation may be read directly from the graduated arc when proper settings are made. At noon, when the sun is on the meridian, the plane of the declination arc and the plane of the latitude arc are the same. The latitude arc is mounted on the horizon circle in a plane perpendicular to it. When the instrument is properly sighted, the observed altitude of any body can be read directly.
Uses for the “Position Finder”
- Solves mechanically all spherical triangles.— Inasmuch as any desired spherical triangle can be set up on the instrument, the solution of the unknown elements can be obtained mechanically.
- Locates true north.—To find true north it is necessary to know the latitude of the place and the declination of the body. With the declination and latitude set on the proper arcs, rotate the declination arc and turn the instrument in azimuth until the spot of light falls on the center mark. When this condition obtains, the pole of the declination arc points true north.
- Corrects compass for both deviation and magnetic declination.—When the direction to true north is determined as described above, the error of the compass can be determined at once.
- The procedure used in solution of great circle problems.
- Computation of great circle initial course and distance.
- Set the latitude of the point of departure on the latitude arc.
- Set the latitude of the destination on the declination arc.
- Set the longitude difference on the hour angle arc.
- Align the collimators.
- 90° minus the altitude arc reading is the distance in degrees and minutes (multiply the degrees by 60 and add the minutes for distance in nautical miles).
- The reading of the azimuth circle is the initial course in degrees east or west from the elevated pole.
- Computation of great circle initial course and distance.
Example: Given, point of departure, Lat. 35°-00' N., Long. 145°-00' E. Destination, Lat. 48°-00' N., Long. 130°-00' W. Required: initial course and distance. Solution: Set 35°-00' on the Lat. arc. Set 48°-00' on the dec. arc (same name). Set 85°-00' (145° E.-130° W.) on H.A. arc. Align the cross wires. Read 28°-26' on the altitude scale, 49° on the azimuth scale.
Answer: 90° —28°-26' = 61°-44' = 3,704 miles. Initial course 49°.
- Computation of intermediate points on great circle course.
- Keep latitude arc set at latitude of point of departure and horizon circle set at initial course.
- Set 90° minus distance to required point on the altitude arc.
- Align collimators by moving hour angle and declination settings.
- Read latitude of intermediate point on declination arc and longitude difference on hour angle arc.
Required: 600 mile point on course (1). Procedure: Set 80° (90° —10°) on the altitude arc and align the collimators. Read 41°-14' on the declination arc, 10°-5' on the hour angle arc.
Answer: Lat. 41°-14' N., Long. 134°-54' E. To determine course at intermediate points set each up as point of departure with original destination. - Gives angle of artillery from true north.—The position finder being small and light can be carried as regular equipment by any artillery unit. Having located true north as previously described, an auxiliary telescope can be clamped to the altitude arc. With any desired angle of fire laid off on the azimuth circle, the gun can be pointed by aligning its sights through the auxiliary telescope.
- Takes the altitude and obtains the altitude intercept. A sample problem (hypothetical).—On April 1, 1937, a large twin-engine naval patrol airplane is en route from Miami, Florida, to Port of Spain, Trinidad. The airplane has been flying on top of a rain storm for some time and the navigator wishes to know the location of the ship. He prepares to make a sun observation at about 9:25 a.m., L.C.T. Based upon the length of time they have been in the air, the speed of the airplane, and the course they have been steering, the navigator estimates the position of the craft to be Lat. 20°-00' N., and Long. 72°-30' W.
He takes the position finder and swings the declination arc over to the side to simplify the use of the position finder as a sextant. The navigator rests the instrument on his lap so that the sun shining through the cabin window shines upon it. He then brings the two leveling bubbles to the center of the tubes, paying more attention to the bubble which is in the plane of the altitude arc. % moving the altitude telescope along the altitude arc, he brings the spot of sunlight on to the cross which marks the geometric center of the position finder. At the instant when the sun spot ls on the cross mark and the bubbles are in the center of the tubes, the navigator looks at his watch. The time is exactly 9:30 a.m., L.C.T., and the altitude is 51°-46'. He writes these values in his notebook and then prepares to compute his Position by the line of position method.
The estimated longitude indicates that he is in the 75th meridian time zone which is 5 hours removed from the Greenwich meridian.
Hence, he add as shown to find the G.C.T.
Local civil time = 9h-30m
Time difference = 5h-00m
G.C.T. = 14h-30m
Looking in the Nautical Almanac on page 13 of the “Sun Tables” for April 1, 1937, and a G.C.T. of 14h-30m he finds that the sun’s declination is 4-31' north of the equator and that the G.H.A. is 36°-30'. To find the G.H.A. he makes a very simple interpolation. When he subtracts the L.H.A. (36°-30') from the estimated longitude (72°-30') he finds the L.H.A. to be 36°-00'. Having these values, he proceeds to use the Position finder to compute his line of position.
With the position finder cradled in his lap, the navigator operates the instrument in the follow- mg manner:
- He sets the declination (4°-31') on the declination arc.
- He sets the estimated latitude (20°-00' N.) on the latitude protractor.
- He sets the L.H.A. (36°-00') on the hour angle protractor.
- He turns the azimuth circle and at the same time moves the altitude telescope along its arc until it is in alignment with the declination telescope.
- When the alignment is exact, he reads the value of the altitude to be 51°-41' and he reads the azimuth to be 109°. The altitude thus found is known as the calculated altitude.
The navigator compares the observed altitude (corrected for refraction) with the computed altitude. The difference:
51°-46’ altitude - 1’ refraction = 51°-45’ corrected observed altitude
51°-45’ observed - 51°41’ calculated = 4’ intercept
Four minutes (4') is known as the intercept and indicates that the true position of the naval plane is 4 nautical miles away from the estimated position. This intercept is plotted along the azimuth line and a line of position drawn at right angles to the azimuth line. When this line of position is intersected with the plotted course line a close check on the position of the airplane is assured.
By taking frequent observations the navigator guides the pilot and the flight is completed in the shortest possible time and without getting off the course. While this narration takes considerable time to tell, the actual operations described are accomplished in a space of about 2 minutes.
The reports of the National Advisory Committee for Aeronautics, Nos. 131 and 198, gave some valuable information as to what results were obtained with nautical instruments then in use by different nations. It also furnished an idea of what was really wanted for the finding of one’s position more rapidly and more accurately than by means of any instrument then in use.
The instrument may be used as a star finder and save the navigator much time in identifying stars.
With the development of the larger airplane for above weather flying, celestial navigation will become absolutely necessary and, no doubt, will be one of the requirements for a pilot to secure his license. In time of war radiocompass and beam flying would be out and celestial navigation would be the only means left.
The optical system of measuring the position of a given celestial body is radically different from any existing method in use at this time. It is the first time that the optical system has been incorporated with a mechanical device for solving the astronomical triangle.
In all bubble sextants or octants the problem is to get two objects together with the result that the observer, in reality, is aiming the sun at a fast moving bubble in a circular field. In the position finder, using the assumed latitude and longitude method and setting same on the instrument, you center the celestial body’s image on the geometric center of the instrument (which we will call the bull’s- eye) and when your eye tells you are on this bull’s-eye you press the trigger and record your intercept. In a way it is similar to bringing the sun’s image to the natural horizon. In almost all cases only one eye is used when a sextant or octant is used, and two eyes can see more than one.
The resume of navigation methods published in the Naval Institute Proceedings, September, 1934, set out 29 methods by as many authors of solving the astronomical triangle for getting a line of position, which shows most navigators have devoted their thought to simplifying the mathematical procedure. I do not know how to work any of these problems as I do not know trigonometry. The only celestial navigation I know is what I learned through the instrument.
The creating and developing of this instrument after being away from the Navy for 29 years was responsible for renewing an acquaintanceship with many officers with whom I served and who are now captains and rear admirals. It also afforded a means for a trip to Europe where I was very successful in interesting foreign instrument manufacturers in buying license rights.
A few months ago, another method of using the instrument occurred to me which, I think, when properly engineered and designed, will give a pilot or navigator a fix more quickly than by any other method in use today. It was submitted to the Hydrographic Office and Naval Academy Navigation Department and has received their approval in principle. I will leave it to the reader to use his imagination to follow my description of the new method as best he can without having the instrument before him.
The instrument allows the observer to set the telescope on the declination arc on the position of the celestial body to be observed for a given time and his assumed latitude and longitude on this earth. To carry out this thought we might substitute a steel ball in a plastic glass (unbreakable) longitudinal tube, having a curvature of 1° to the inch, divided into 2-minute graduations, with 1° on each side of the center of the azimuth plate and in line with the altitude arc. On top of the plate, to the left of this recording tube, install a stop watch which is connected with the thumb trigger to the right of recording tube. The pressing of this thumb trigger when the sun or moon’s image is centered in the f-in. circle in the middle of the azimuth plate stops the watch’s second hand, furnishes his time of observation, and the ball indicates his intercept in minutes (which are nautical miles) and whether he is away or towards his assumed position. The azimuth reading on the instrument can then be plotted on the chart and the observer has his fix with reference to the position he assumed on the chart and on the instrument (Sumner Line).
I have worked out a form which fits in a container on the azimuth plate and allows the observer to do his work more quickly and without the use of some one to take time when he makes an observation.
It is my ambition to develop this instrument to a point where a novice can do accurate piloting on board ship or in a plane without the aid of others and at a speed that will allow him to know when he has encountered a drift and correct his course accordingly.