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AN ANCIENT ASTRONOMICAL INSTRUMENT.

KURT LAVES.

Some years ago I happened to see in the Ethnological Museum at Berlin among a collection of East Indian curiosities a small rectangular board about three inches by four, to the middle point of which a chord of about ten inches was fastened. A number of knots were tied into the string and on the one side of the board some words in foreign characters were visible. The explanation given by the label, attached to this item of curiosity, was, that the board was used by the tribes of the west shore of East India, accustomed to sea-faring life, for the purpose of determining their latitudes at sea.

It is evident how the little device can be used for this purpose. Holding with the one hand the board in a vertical position, so that the longer edges are horizontal, the observer with his face to the North Star can bring the upper edge to pass through the star whilst the lower edge is touching the horizontal line all the time, keeping the middle point of the board level with his eye. Stretching the cord to the tip of his nose and marking this point, the observer will have approximately determined the length of one of the equal sides of the isosceles triangle, which has its vertex in the eye of the observer; its base is formed by the vertical line passing through the middle point of the board. I have said, that the string measures one of the sides and not the height of the triangle, since it is stretched to a point nearly half the length of the base below the vertex of the triangle. The facial differences of the different observers must have established such a strong personal equation, as to limit each observer to his own apparatus. If we assume for a moment, that the North Star actually coincides with the North Pole, we can imagine, that the ancient observers needed only to find on land the lengths of the string for a number of conspicuous land marks of the shore, to have a ready means of finding between the latitudes of which two standard places their boat was located. Indeed we know the base b and the side I of the isosceles triangle, we have, therefore, when we call the angle at the vertex L

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L will be the altitude of the North Star or the latitude of the ob. server in our hypothesis. The rudeness of the method is apparent with its many and conspicuous defects, still there is a certain ingenuity in this proceeding cognate to that displayed in the in

vention of the gnomon. But there seems to be a serious difficulty when we give up our hypothesis, that the daily apparent orbit of the North Star is reduced to a point. It is obvious, that when we determine the reference points in the string from observations of the North Star in upper culmination, we would arrive at absolutely erroneous results. The same is true when the star is in lower culmination. We can hardly assume, that the ancient observers had provided for that purpose a table of correction. A much simpler explanation appears to me to be the following: The great monsoon winds always occur at the same seasons of the year once in a southward, and once in a northward direction. Upon them communications between distant tribes of the East Indian shore have been dependent from times immemorial. Their two seasons are half a year apart and begin with January and July respectively. In the early evening hours of January, the Pole Star is near its upper culmination, in July near its lower culmination. If the ancient navigators were provided therefore, for the southward trip in January, with a set of reference points based upon observations in upper culmination, and for their northward journey in July with one derived from lower culmination, it seems that the difficulty would be easily remedied. It would seem therefore not improbable, that the little instrument in the Berliner Museum was invented for the very purpose of making possible these great and periodical journeys to distant shores. Since the East Indian peninsula lies between +25° aud+70° it is obvious that in these low latitudes the instrument is at its best, in as much as a small change in latitude will produce an appreciable change in the length of the string. Indeed

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varies between 5 and 11 in this interval of latitudes from 25° to 7° so the string at Cap Camorin will be about 16 inches with 3 inches and at the mouth of the Indus about 7 inches. THE UNIVERSITY OF CHICAGO,

b

1900 Oct. 30th.

BURCKHALTER'S

APPARATUS FOR
THE SOLAR CORONA.*

PHOTOGRAPHING

Charles Burckhalter's successful invention which enabled him to secure such excellent photographs at the Georgia eclipse last * Extracts from an article that recently appeared in the Oakland Inquirer.

May is bringing much favorable notice both to himself and the Chabot Observatory of Oakland, with which he is connected. The leading astronomers of the world unite in declaring that Professor Burckhalter's invention is an important addition to the science and that it will probably lead to discoveries in the study of the Sun's corona.

As has been noted before, Professor Burckhalter's invention consists of a device whereby both the brighter and darker portions of the Sun's corona may be photographed at the same time. Professor Burckhalter was able to give his invention a thorough test at the Georgia eclipse last May, thanks to the generosity of John Dolbeer, a San Francisco business man who takes much interest in astronomy and who provided the necessary funds for the expedition. William M. Pierson of San Francisco had previously presented a photographic telescope to Chabot Observatory and Dr. George C. Purdee of Oakland had provided a duplicate lens and both of these instruments were taken to Georgia for use in the eclipse, most successful results being obtained, as can be judged from the extracts of letters from the astronomers given below.

Professor C. A. Young of Princeton Observatory, writes as follows:

"I congratulate you most heartily on your practically perfect success. All six of your revolver plates are admirable and the way in which different exposures and developments of positives made from a single negative bring out quite different details is very interesting, as exemplified in the two pairs of pictures madefrom your negatives 7 and 8."

Professor George E. Hale, director of the Yerkes Observatory, has the following to say:

"Many thanks for your kindness in sending the lantern slides of your photographs of the corona. They certainly show very clearly the advantage of your method of exposing and I only wish it were not too late to publish them with the other eclipse photographs in the Astronomical Journal."

Professor E. C. Pickering of Harvard College Observatory

says:

"Your letter and the lantern slides arrived safely. The latter are very interesting and ought to give us many new facts regarding the corona."

Professor J. E. Keeler, the late director of Lick Observatory, wrote shortly before his death as follows concerning the results. of Professor Burckhalter's work at the Georgia eclipse:

"I congratulate you heartily on the success of your method and the final results you have obtained with it. While the the corona is less interesting than that of the India eclipse, your negatives are technically more perfect than those secured on that occasion."

Professor A. O. Leuschner, who is in charge of the students' Observatory of the University of California, had this to say:

"Please accept my sincere thanks for the fine slides from your photographs of the recent solar eclipse. There is no doubt in my mind that your method of obtaining composite photographs of the solar corona is an immense success and I extend to you my sincere congratulations on your fine work.”

Captain William Noble, a prominent member of the Royal Astronomical Society of England, expressed himself as follows: "I am delighted with them-there is no other word for it-and thank you most sincerely for so really beautiful and valuable a gift. It seems invidious to pick out one when all are so excellent, but I gravely doubt if 'No. 1' has ever been surpassed as a picture of the region immediately surrounding the Sun's limb, or 'No. 6' as a view of the entire solar surroundings. You ought to feel most uncommonly proud of yourself and of your really brilliant and original invention."

In writing concerning the sending of copies of Professor Burckhalter's photographs of the eclipse to Flammarion, the great French astronomer, M. J. Costa, the Consul of Uruguay at San Francisco, says:

"It is a pleasure to me to notify you that the great astronomer, Camille Flammarion, has received, through J. C. Cebrian, your photographs of the Sun's corona and he has pronounced them the best he has seen and he is going to print them in his paper, (Astronomie Popularie). He will write you about some details of said photographs."

Dr. L. Weinek, director of the Royal Observatory of Prague, Austria, says:

"I must confess that I have never seen such clear eclipse photographs with protuberances and a perfectly sharp rim of the Moon and I congratulate you upon the wonderful, astonishingly beautiful results."

*

In writing to John Dolbeer, who furnished the funds for the Chabot expedition Dr. Weinek said:

"At your kind suggestion, Mr. Charles Burckhalter, director of Chabot Observatory, Oakland, has sent me five splendid positives of this year's total eclipse of May 28th, taken at Siloam,

Georgia; they arrived here on September 29th in perfect condition. I am exceedingly gratified to possess these pictures which show the corona in an incomparably beautiful and clear manner. I congratulate you upon your great-heartedness in sending this expedition as well as Mr. Burckhalter upon the wonderful results obtained by his method of control. I have never seen even on the best eclipse photographs taken in any country and by any astronomers, the corona as a whole with the protuberances as they are shown in numbers 6 and 8. The protuberances on number 10 also show a surprising sharpness and distinctness."

Professor Edward S. Holden, formerly director of Lick Observatory, who is now in New York, expressed himself in the following enthusiastic manner:

"I've just received your splendid box of slides and given some little time to examining them. They are most instructive and do you the greatest credit. It is all your own plan, invented throughout and carried out unaided and these slides are a positive addition to science. I mean to study them. in connection with other slides I have in New York and expect to learn much. The detail is wonderful and they are a success. I thank you sincerely for the chance of seeing them and congratulate you heartily."

W. H. Wesley, secretary of the Royal Astronomical Society, England, wrote, "the detail near the Moon's limb is marvelous and shows the immense superiority of the method."

Highly commendatory articles have also appeared in various astronomical journals, testifying to the importance and value of Professor Burckhalter's invention.

ASTRONOMY.*

DR. A. A. COMMON.

The progress of the new astronomy is so closely bound up with that of photography that I shall briefly call to mind some of the many achievements in which photography has aided the astron

omer.

Daguerre's invention in 1839 was almost immediately tried with the Sun and Moon, J. W. Draper and the two Bonds in America, Warren de la Rue in this country, and Foucault and Opening Address by Dr. A, A. Common, F. R. S., F. R. A. S., Chairman of the Department of Astronomy, at the Bradford meeting of the British Association for the Advancement of Science. Continued from page 424.

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