The phonoscope (Nov 1896-Dec 1899)

8 THE PHONOSCOPE Zo XEafce flfcovtng (pictures of the Sun's Eclipse Marvellously Elaborate Preparations to flake Permanent Records of the Great Natural Phenomenon A journey of between three and four thousand miles in order to do fifty-five seconds' work. It sounds like a quixotic undertaking, but Professor David P. Todd and Mr. Percival Lowell, the men who are now making the journey, do not regard it in that light. If the fifty-five seconds of work to perform which they are going all the way from here to Tripoli, in Northern Africa, is successful it may result in knowledge of the higest scientific value. The enterprise on which these two scientists have embarked is the observation of the total eclipse of the sun, which is to occur May 2S next. It would not be necessary to go all the way to Africa merely to see it, for this particular eclipse will be visible from the southern part of the United States. But in making astronomical observations of so important an event as this it is necessary to take advantage of every favorable influence. The thing that most frequently interferes with eclipse observations is cloud} weather. The likelihood of clouds in Tripoli, shielded as it is by the Atlas Mountains, and near the borders of the Sahara Desert, is nearly fifty per cent less than at any point in this country. Therefore these scientists are going to transport themselves and their instruments to this distant spot so that their chances of success ma}' be as bright as possible. Professor Todd may be described as an expert in the observation of eclipses. Three years ago he went to Japan with a party for this purpose, and he has headed a number ol similar expeditions to different parts of the world. He has devised a number of instruments for use in eclipse work. With his wife, who is also an astronomer of rare attainments, he is the author of a book on "Total Eclipses of the Sun," which is an authority on the subject. Professor Todd hopes to be able on his return from his present journey to add a very interesting chapter to this book. Mr. Percival Lowell, who accompanies Professor Todd, is well known for his work in astronomy through the observatory which he supports in Arizona and in many other ways. It was at his instance that the present expedition was undertaken. Although the period during which the face of the sun will be completely hidden on May 28 will be of brief duration, there probably never has been an eclipse for which more thorough preparations for the purpose of taking observations was made. A number of new instruments, several of them the invention of Professor Todd, will be employed for the first time. Another device which is to be brought into use at the suggestion of Professor Todd will utilize a recent invention in the cause of science. As is generally known the chief method of gaining information about the sun is by taking photographs during the progress of an eclipse. This year, under the direction of Professor Todd, the biograph will be employed for this purpose and moving pictures of the progress of the eclipse will be made both in this country and abroad. Arrangements have been made by a biograph company to send expert operators to a favorable point in the path of the eclipse through this country. On the other side a party from either the British or French bit graph company will accompany the professor and his assistants to Africa to make similar views. By making practically a continuous record of all that goes on in the vicinity of the sun during the progress of the eclipse the observations will realize the highest possible value. As is generally understood, the obscuration of the sun known as an eclipse is due to the presence of the moon directly between the sun and the earth. The surface of the moon is so much smaller than that of the sun that in spite of its relative nearness it casts only a very narrow shadow. Moreover, the movements of both earth and moon are so rapid that an eclipse can last but a few minutes under most favorable conditions. The longest possible duration of totality is about eight minutes. That might occur at the equator. Receding from there in either direction the length of time during which the sun's face is completely darkened becomes less and less. The longest period during which the sun will be hidden during the approaching eclipse at an_v point from which it may be observed is less than two minutes. The path of this eclipse is somewhat unusual. It is the first one observable from any part of the Unit»d States since 1S89, when numerous observations were made in California and the Northwest. In the eclipse of May 28 the point of the moon's shadow will touch the earth somewhere out in the Pacific Ocean. Thence it will sweep along at the rate of a thousmd miles an hour, reaching land on the west coast of Mexico, crossing that country in a northeasterly direction, and arriving in the United States at New Orleans, where it will be total at half-past seven a. m., the period of totality lasting one minute and seventeen seconds. In crossing the United States the path of the eclipse follows a line from New Orleans to Norfolk, passing across the States of Mississippi, Alabama, Georgia, the Carolinas and the southwestern corner of Virginia. The region which will be temporarily in darkness will be a strip about fifty-four miles wide along the route. Leaving the coast at Norfolk the eclipse sweeps on in the same direction until it reaches a point in the Atlantic at latitude 45 degrees north. This is the northern extremity of its course and will be reached at noon. If it were on land it would be the most desirable station from which to watch the eclipse, for the period of totality will continue for two and one-quarter minutes. But the difficulties of making observations from shipboard render it impracticable to study the eclipse from this point. Turning to the southeast at latitude 45 degrees the eclipse will travel on across the Atlantic to the coast of Portugal, where it is timed to arrive at half-past three P. M. It will cross to Alicante, on the east coast of Spain. From here the path will lead across the Mediterranean to Algiers, over Tripoli, where the duration of totality will be fiftyfive seconds and where Professor Todd will make his observations at nineteen minutes past five P. M. The remainder of the course is across the desert and northeastern Africa, ending near the Red Sea. It is interesting to note the careful and thorough preparations which are made for the study of an eclipse. For example, during the last four vears the United States Weather Bureau has been making observations along the path of the eclipse in this country in order to determine the region of least cloud. As a result of these observations a point lias been selected, where the prospect of clear weather is the most favorable. This point is near Columbus, Ga., in the southern foothills of the Alleghanies, and it is here that the American party will watch the eclipse and photograph it by means of the biograph apparatus. One interesting feature of the approaching observation is a plan by which Professor Todd expects to steal a march on the eclipse and secure complete co-operation between the parties of observers on opposite sides of the Atlantic. This plan will be carried out through the aid of the telegraph and cable lines connecting the two or more points from which observations will be made. A direct line along the path of the eclipse from New Orleans to Tripoli will be cleared at the beginning of the observations, and a cipher code will be arranged for the quick transmission of in formation between the different parties. Thus, as soon as the observers in Georgia or Alabama have completed their work the result will be wired to Professor Todd and his assistants in Tripoli in advance of the appearance of the eclipse at that point. The carrying out of this plan will add greatly to the value of this work, for it will enable the party in Tripoli to verify any peculiar phenomena detected by the scientists on this side. For example, one thing that the observers are to look for is an inter-Mercurial planet — that is, a planet with its orbit nearer the sun than is that of Mercury. If such a planet is detected on this side of the Atlantic the watchers in Northern Africa will be informed, and will make a special effort to verify the discovery. By arranging the course and the code in advance it will be possible to do this with time to spare, notwithstanding the tremendous pace at which the eclipse will travel. Professor Todd sailed from New York on his expedition on January 17. Before his departure he explained his plans and permitted a representative to see some of the special apparatus which he has designed, and which is to be brought into use for the first time on May 2S. Among this is a 24-inch lens, which is to be used in the photographic work. The largest ever employed heretofore was a 13-inch glass. The use of the more powerful lens will add greatly to the possibilities of securing important results. "One attempt which we shall make," said Professor Todd, "is to secure a satisfactory photograph of the solar corona. The corona is the irregular boundary of light which surrounds the disk of the sun when the latter is darkened. To photograph it has proved a matter of difficult}', because it varies so much in brilliancy from its outer to its inner border. In an exposure for the outer portion the brilliancy of the inner part destroys the reproduction of that part of it. On the other hand, an exposure sufficient to catch the inner section loses the outer portion entirely. "To overcome this difficulty I devised an apparatus intended to secure a gradual exposure of the different portions. I built this some years ago and took it to Japan with me. I was unable to use it there, but will make the attempt again this year. "The machine is automatic in its operation, and is controlled by electricity. It employs an ordinary telescopic lens, but between the lens and the plate is interposed a metal disk, surrounded by thin metal rings, which fit closely together, but may be worked separately by means of small levers. By lifting these rings one at a time a varying length of exposure is secured, which is expected to equalize the varying degrees of brilliancy in the corona itself. The plates recording the image are mounted on a hexagonal 'barrel' behind this metal shield, and can be revolved so as to secure a rapid succession of views. It is hoped by this means to obtain a satisfactory photograph of this interesting phenomenon. "Another device which I shall employ I call the 'electric commutator.' It provides for the operation of multiple telescopic cameras, so that a number of views may be taken in rapid succession or simultaneously if desired. With the addition of the biograph apparatus we hope to get results equivalent to those that would ordinarily be obtained by multiplying the duration of totality tenfold. Of course, in such an undertaking as this it is impossible to predict any result whatever with