vation does not give a location, but only a line passing through the position of the observer. Such lines are called 'Sumner lines.' If the latitude or longitude of the point of observation is known or its direction or distance from some known point, the position of a Sumner line may be determined.

"In the present case we have both the direction and the estimated distance from Amsterdam Island to give the position on the Sumner lines resulting from the sextant observations of the altitude of the

sun.

DIRECTION OF FLIGHT KNOWN WITH
GREAT PRECISION

"The resulting positions obtained by using the direction may differ from those obtained by using the estimated distance. This is to be expected. The distances depend upon estimates of speed, and estimates of speed depend upon the altitude of the plane obtained with an aneroid barometer.

"The barometer readings of altitude depend on the assumption that the sea-level atmospheric pressure remains constant over the whole route of the flight, something which in ordinary latitudes rarely happens between points so widely separated. We do not know if these conditions are better in the Polar Regions. It is our belief, therefore, that estimates of speed may be subject to large errors.

"But the direction of flight from Amsterdam Island could be known with a comparatively high degree of precision, as it depended only on the skillful use of two optical instruments, the drift indicator and the sun-compass, both capable of giving the direction within one degree. When these instruments were used almost continuously, as they were, it seems probable that the route flown followed closely the route planned, the deviations to the right tending to balance the deviations to the left.

"Attention is called to the fact that the Sumner line determined at 4 hours 56 minutes, coinciding so nearly in direction with the direction of flight, gives a splendid determination of longitude and check on his steering at a point about midway of the flight, just as the one determined at the Pole and intersecting the course at an angle of about 56 degrees gives a good

condition for the determination of latitude.

"The amount which the plane may be actually off the Sumner line is not affected by inaccuracies of steering, such as enter into the holding the compass course, or determining and correcting for drift, but are wholly due to errors in the observed elevation of the sun. These elevations were determined with a sextant, in which the bubble supplies the horizon of reference, an instrument developed by Commander Byrd and in the use of which he was most skillful.

"An estimate of the error attending such an observation may be obtained by fitting the dead reckoning to the Sumner lines and by a consideration of the capacity of the sextant. From this evidence, it is believed that five miles, plus or minus, represents a reasonable estimate of the limits of this error, which is not accumulative, but is the same for all Sumner lines thus determined.

"It may be noted, also, that in comparing positions determined at 8 hours 18 minutes, 8 hours 38 minutes, and 8 hours 59 minutes, it becomes necessary to assume errors of only two minutes in the observed altitudes to bring them into full accord with the average speed between the determined positions. This would indicate that 5 minutes is a very reasonable limit to assign to the uncertainty of an observed altitude.

ARRIVAL AT POLE THREE MINUTES PAST NINE IN THE MORNING

"At 8 hours 58 minutes 55 seconds an observation of the altitude of the sun gave a latitude of 89° 55.3′ on the meridian of flight. This point is 4.7 miles from the Pole. Continuing his flight on the same course and at the speed of 74 miles per hour, which he had averaged since 8 hours 18 minutes, would bring Commander Byrd close to the Pole in 3 minutes 49 seconds, making the probable time of his arrival at the Pole 9 hours 3 minutes, Greenwich civil time.

"At the time Commander Byrd was close to the Pole he estimated the moment of his arrival there at 9 hours 2 minutes. Our calculations differ from his estimate less than one minute, during which time he would have flown about one mile.

From this it appears that he chose the right place to maneuver.

"Flying his plane to the right long enough to take two sextant observations, he turned around and took two more observations. These four observations confirmed his dead-reckoning position of the Pole. He then attempted to fly his plane in a circle several miles in diameter, with his Pole position as a center.

EXPLORER'S FIELD OF VIEW OVER POLE A

CIRCLE 120 MILES IN DIAMETER

"Flying at and about the Pole at an altitude of 3,000 feet, Commander Byrd's field of view was a circle more than 120 miles in diameter. The exact point of the North Pole was close to the center of this circle, and in his near foreground and during more than two hours of his flight was within his ken.

"Soon after leaving the Pole, the sextant which Commander Byrd was using slid off the chart table, breaking the horizon glass. This made it necessary to navigate the return trip wholly by dead reckoning.

"In accomplishing this, two incidents should be specially noted. At the moment when the sun would be crossing the 15th meridian, along which he had laid his course, he had the plane steadied, pointing directly toward the sun, and observed at the same instant that the shadow on the sun-compass was down the middle of the hand, thus verifying his position as being on that meridian. This had an even more satisfactory verification when, at about 14 hours 30 minutes, G. C. T., he sighted land dead ahead and soon identified Grey Point (Grey Hook), Spitsbergen, just west of the 15th meridian.

"It is unfortunate that no sextant ob

servations could be made on the return trip; but the successful landfall at Grey Hook demonstrates Commander Byrd's skill in navigating along a predetermined course, and in our opinion is one of the strongest evidences that he was equally successful in his flight northward.

"The feat of flying a plane 600 miles from land and returning directly to the point aimed for is a remarkable exhibition of skillful navigation and shows beyond a reasonable doubt that he knew where he was at all times during the flight.

"It is the opinion of your committee that at very close to 9 hours 3 minutes, Greenwich civil time, May 9, 1926, Lieutenant Commander Richard Evelyn Byrd was at the North Pole, in so far as an observer in an airplane, using the most accurate instruments and methods available for determining his position, could ascertain.

"Respectfully submitted,

"HUGH C. MITCHELL.
"ALBERT H. BUMSTEAD.
"HENRY G. AVERS."

COPIES OF DATA FILED WITH OTHER
SOCIETIES

After the Secretary of the Navy had received the Report of the Special Committee of the National Geographic Society, corroborating in every particular Commander Byrd's data which established his right to the distinction of being the first man to reach the North Pole by aërial navigation, the explorer transmitted certified copies of his data and photographic reproductions of his charts, together with true copies of the Report of the Special Committee, to a number of the leading geographical societies of the world for their archives.

HENRY WHITE, Vice-President

O. P. AUSTIN, Secretary GEO. W. HUTCHISON, Associate Secretary EDWIN P. GROSVENOR, General Counsel

TO carry out the purposes for which it was founded thirty-eight years ago, the National Geographic Society publishes this Magazine. All receipts are invested in the Magazine itself or expended directly to promote geographic knowledge.

ARTICLES and photographs are desired. For material which the Magazine can use, generous remuneration is made. Contributions should be accompanied by an addressed return envelope and postage.

IMMEDIATELY after the terrific eruption of the world's largest crater, Mt. Katmai, in Alaska, a National Geographic Society expedition was sent to make observations of this remarkable phenomenon. Four expeditions have followed and the extraordinary scientific data resulting given to the world. In this vicinity an eighth wonder of the world was discovered and explored-"The Valley of Ten Thousand Smokes," a vast area of steaming, spouting fissures. As a result of The Society's discoveries this area has been created a National Monument by proclamation of the President of the United States. AT an expense of over $50,000 The Society sent a notable series of expeditions into Peru to investigate the traces of the Inca race. Their

discoveries form a large share of our knowledge of a civilization waning when Pizarro first set foot in Peru. THE Society also had the honor of subscribing a substantial sum to the expedition of Admiral Peary, who discovered the North Pole. NOT long ago The Society granted $25,000, and in addition $75,000 was given by individual members to the Government when the congressional appropriation for the purpose was insufficient, and the finest of the giant sequoia trees of California were thereby saved for the American people.

THE Society is conducting extensive explorations and excavations in northwestern New Mexico, which was one of the most densely populated areas in North America before Columbus came, a region where prehistoric peoples lived in vast com munal dwellings and whose customs, ceremonies, and name have been engulfed in an oblivion.

THE Society also is maintaining expeditions in the unknown area adjacent to the San Juan River in southeastern Utah, and in Yunnan, Kweichow, and Kansu, China-all regions virgin to scientific study.