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THE CITY OF BAKER, OREGON (LOWER PICTURE)
Baker is situated at an altitude of 3500 feet and promised to afford to the observers of the United States Naval Observatory an excellent opportunity to study the eclipse, with an abundance of clear sky in June; as it turned out, however, cloudy weather nearly prevented the work of the expedition. The city is on the main line of the Union Pacific system to Portland, a fact taken into consideration in the selection of the site on account of the necessary transportation of numerous instruments
which had boasted a railroad for only four years, but where civilization had existed for more than 2200 years as was shown by an old Roman fort still in a good state of preservation. A visit from the New World to this old and worn-out kingdom was not without its fascination.
The eclipse of the year 1918 took place on June 8. The shadow of the moon first touched the earth's surface on the Pacific Ocean, far south of Japan. Due to the revolution of the moon about the earth, and to the rotation of the earth on its axis, the moon's shadow crossed the Pacific Ocean at a speed well over a thousand miles an hour. It was well after noon before the shadow reached the American continent, and the eclipse began in the state of Washington. Here the width. of the shadow was only sixty miles so that only those fortunate enough to be within this narrow track were able to see the eclipse in its totality. The eclipse passed southeasterly through Washington, Oregon, Idaho, Wyoming, and Colorado in succession. In Colorado the shadow had dwindled to forty miles in width. After passing through some of the central states, the shadow left the United States at Florida and left the earth's surface in the Atlantic, off the coast of the Bahama Islands.
The eclipse was seen almost exclusively from the United States, and so it will be known as the American Eclipse of 1918. As more than half the civilized world was in the grip of the tremendous war, it was necessary for the American astronomers in the year 1916 and early in 1917 to make their plans to see to it that this eclipse should be well observed. Before our own country had become involved in the war, Congress had been asked for and had made a special appropriation to defray the expense of equipment and travel for the party from the United States Naval Observatory.
The exact location of an eclipse site
is of the greatest importance, since the utmost care must be exercised to choose one where the chances of clear skies will be as great as possible. Think of the disappointment of finding only cloudy. skies on the all-important day! Even one small, dense cloud hanging over the sun during totality would render useless all the active months of preparation, would make of no avail the delicate apparatus carefully adjusted after arduous toil, and make of no account the carefully prepared plans for scientific work. The majority of the members of the Naval Observatory party to Sumatra in 1901 had no results to show for their long trip which consumed about six months. Not only must a location be chosen where good weather is promised, but the location. should be convenient to a railroad, and at or near a town so that the observers may be properly housed and fed without the necessity of forming a camp with extra arrangements for cooking, etc. In addition, most classes of eclipse work require a location as near as possible to the central line of the moon's shadow.
In order to help the astronomers make as intelligent a choice of an eclipse site as possible, the Naval Observatory, in 1917, had prepared a large scale map of the United States showing among other things, railroad lines, contour lines, and the location of towns, within the eclipse track. The city of Baker, in eastern Oregon, seemed to be the ideal spot for the government party, since the weather of early June promised an absence of rain, with an abundance of clear skies. This city, of about ten thousand inhabitants, is on the main line of the Union Pacific system to Portland, and at an altitude of about 3500 feet.
In order to set up and adjust the apparatus, five of the party left the East about April 20. The party consisted of Mr. J. C. Hammond, Astronomer of the Naval Observatory, in charge of the
THE TOTAL SOLAR ECLIPSE OF 1918
expedition, Mr. W. A. Conrad and Mr. C. C. Wylie, assistants at the Naval Observatory, and Dr. L. G. Hoxton and Dr. S. A. Mitchell, of the University of Virginia. After locating ourselves at the Antlers Hotel, we viewed the city in order to find the best site for the eclipse location. Through the kindness of the Chief Engineer of the Union. Pacific system, who provided us with excellent photographs and topographic maps, we were not long in deciding upon the Fair Grounds on the edge of the city as the most convenient spot. This was fairly near to the hotel where we lived, the grounds were surrounded by a high board fence which would serve to keep out the idly curious, and the buildings in the grounds were adequate to house our valuable apparatus until put in place. We were in Baker exactly six weeks before eclipse day, and the time was none too long. The apparatus was sent forward by through freight, and although we greatly feared delays, it arrived safely the second day after our own arrival. To assist in the work of erecting the apparatus, the superintendent of the Naval Observatory had requested the services of five sailors from the United States Naval Station at Bremerton, Washington, who were in charge of a chief petty officer. The sailors were carpenters and machinists who assisted the astronomers in splendid style so that ten days before the eclipse, when the rest of the party began to arrive, the apparatus was all erected and partly adjusted, and there remained only the perfecting of the adjustments in order to be ready for the all-important day of the eclipse.
An idea of the scope and difficulty of the work to be attempted may perhaps be best visualized by the realization that it took five astronomers and half a dozen sailors six weeks to have things ready for the final adjustments.
But what, people ask, is to be learned at the time of an eclipse? Why these expeditions which at times go so far
afield, these elaborate preparations which must run the risk of accomplishing nothing on account of the clouds? Surely there must be something of great importance to be learned in order to warrant such an expenditure of energy and money. Perhaps the best way to answer these questions would be to take up in detail the scientific program of the party of the United States Naval Observatory which was carried out at Baker, giving a brief account of the apparatus necessary and the problem attacked.
The first problem for a government expedition to attempt must necessarily be the determination of the precise times of contact of the limbs of the sun
and moon. The American Ephemeris and Nautical Almanac is published each year in Washington at the Naval Observatory. This book gives the exact place of the sun, moon, planets, and stars; for each and every day at noon, in the case of the sun, for each and every hour for the moon, and at longer intervals for the planets and stars. The positions are tabulated three or four years in advance, and the positions determined are constantly checked up by observations. On account of the fact that the moon is such a near neighbor, its motion is very complicated. It is very necessary to make the computed positions agree with those calculated. One of the best ways of finding the exact position of the moon is to note the times of contact of its limbs with those of the sun at the time of an eclipse. At the eclipse of 1905, the programs of observation were somewhat disarranged by the fact that total eclipse took place ten seconds earlier than the calculated time. In 1918, it was expected that the eclipse in Baker would begin about twelve seconds earlier than the time as computed from the American Ephemeris. To compute the phases of the eclipse one must know with accuracy the exact latitude and longitude of the eclipse location. This part of the
eclipse work in Baker was under the direction of Mr. J. C. Hammond of the Naval Observatory, and in the observations he was assisted by Mr. Wylie, by Mr. Conrad, and, to a lesser degree, by Chief Petty Officer Patrick Welsch. The latitude and longitude were determined by observations on stars on a dozen or more nights during the weeks of preparation for the eclipse. Since longitude is measured by the difference in time between any two places, it was necessary to determine the exact time at Baker, and at the same instant find the exact time at Washington. Since the longitude at Washington with respect to Greenwich is known, this would give the longitude of Baker with respect to Greenwich. In order to determine the difference in time between Washington and Baker, it was necessary to connect the two places with a direct telegraph line. On switching on the current, the beats of the clock could be heard by the relay in Baker, and a record of these could be made by means of the chronograph. Similarly, the beats of the chronometer used in Baker could be recorded in Washington. In this manner signals were exchanged between the two places on four different nights, with the result that the exact location of the eclipse site on the surface of the earth is known within an error that does not exceed fifty feet.
There is a popular belief to the effect that since a telescope is used to magnify objects, and to show them in greater detail, then of necessity a very large telescope must greatly enhance the beauties of all objects in the sky and make the corona even more beautiful than it appears to the naked eye. This, however, is not the case. This splendid feature of the eclipse owes its charm to its delicate shadings of pearly light, stretching at times to two, three, or more diameters of the sun from its surface. But increase of magnifying power usually means decrease in the
size of the area visible at one time, so that while a great telescope shows a small portion of the corona highly magnified and in great detail, the beauty of the spectacle as a whole is lost. As a matter of fact, the most satisfactory view of the corona is obtained with the naked eye, though a good pair of field glasses may aid in showing some of the features in better detail. The telescope used by Mr. Hammond on June 8 for observing the times of contacts was not a large telescope, but one of the moderate size of five inches in aperture.
During the weeks of preparation, an opportunity was afforded the citizens of Baker to view the moon and some of the planets and brighter stars through this instrument, and many availed themselves of the chance to see the "Man in the Moon," often standing in line for an hour or more, with the thermometer near the freezing point, in order to get their turn for a “look through."
The scientific program of the party which was readily understandable to the residents of Baker who came to the Fair Grounds to see the apparatus erected was the work of the cameras, large and small. These telescopes or cameras were used on eclipse day to photograph the corona and prominences with a greater or less scale. A camera of short focal length gives only a small sized picture, an ordinary kodak showing the sun about the size of the head of an ordinary pin. The greater the focal length of the camera employed, the larger the resulting photograph of the sun. The largest camera used at Baker had a focal length of no less than sixty-five feet. We are all of us familiar with the use of a kodak and the methods by which snapshots are taken, but how handle such a big camera? There are but two methods. One is to mount the huge instrument in such a fashion that at eclipse time it will point directly at the sun. A simple calcula
THE TOTAL SOLAR ECLIPSE OF 1918
tion serves to orient the camera correctly, but the satisfactory erection is a more difficult matter, since any shake given to the camera itself would be communicated to the lens and to the photographic plate. Even a very slight disturbance of the camera would blur the photographed image and make it scientifically useless. But how support such a huge instrument without a tremor? Even a gentle wind would be sufficient to shake it, and eastern Oregon promised an almost certain high wind at eclipse time. This problem
solved by Schaeberle of the Lick Observatory twenty-five years ago, when it was found necessary to build a double tower, the inner one of which supported the lens while the outer one acted as a wind screen. Another complication arises due to the fact that the exposures necessary to obtain the corona last for many seconds of time, sometimes totaling sixty or even one hundred in length. With a telescope of sixty feet focal length, the westerly motion of the sun in the sky causes the image of the sun to move on the photographic plate about one eighth of an inch every minute. Evidently some mechanism must be used to counteract this motion. This is accomplished by a clock mechanism, the details being thoroughly understood.
The Lick Observatory of the University of California has been most assiduous in its observations of eclipses, and more than a dozen expeditions have been sent out to all parts of the globe. This splendid scientific record has been made possible through the generosity of Mr. William H. Crocker, of San Francisco. The Lick parties have always adopted the same method of photographing the corona-that of pointing their camera directly at the sun.
Owing to the difficulty of erecting a double tower, most other astronomers follow the mechanically simpler plan of laying the camera tube horizontally and allowing sunlight to be fed into it by
means of a plane mirror driven by clockwork to counteract the westward motion of the sun. Needless to say, the irregularities of the driving mechanism Iwill affect the exact definition of the photograph-this being the chief drawback to this type of mounting. In addition to the sixty-five foot telescope, the Naval Observatory had two smaller cameras, of 104 inches and 36 inches respectively. On eclipse day, the large instrument was in the hands of Mr. W. A. Conrad, of the Naval Observatory staff, and the successful completion of his program demanded that Mr. Conrad remain closed inside his darkroom during the whole of totality with never a single chance to gain even a glimpse of the corona. The other cameras were used by Mr. G. H. Peters and Mr. C. C. Wylie, also of the Naval Observatory staff. Two smaller cameras pointing directly at the sun were employed by Mr. Kempton Adams.
Photographic work of a vastly different character from that of these cameras, large and small, was demanded by the spectroscopic work. At the eclipse which took place just fifty years ago, in 1868, the spectroscope was employed for the first time. By its use, Janssen in India saw the bright lines in the spectra of the prominences which proved that these outbursts from the sun were masses of heated hydrogen gas. These flames from the solar furnace are shot to enormous distances from the surface of the sun, being sent upward at times with a velocity of one hundred miles a second! Such colossal distances as 480,000 miles from the surface of the sun have been reached. How puny in comparison with such outbursts on the sun are the explosions of dynamite, or the deadly TNT on this little earth of ours!
The spectroscopic work at the time of an eclipse is for the purpose of supplementing such information as is gained daily by the same instrument. The most famous observatory in the