is not controlled. No. 5 is the exposure of a plate for eight seconds of time, in the ordinary way, both for the inner and for the outer corona, and it is seen that the effect is about the same as that which is observed in any of the good photographs of the corona taken during the last eclipse. No. 6 shows the application of a piece of apparatus designed to control and adapt the time of exposure of a plate, so as to give less time to the bright, inner corona, and more time to the outer faint part, and thus to avoid over exposure of the former, and under exposure of the latter when it is desired to photograph both parts at the same time, on the same plate. Evidently the difference between the two pictures is marked, and largely in favor of the controlled method in securing details in all parts of the corona at the same time in a single exposure. These pictures were both taken at the same time, and the total exposure of each was eight seconds. The figures at the top of No. 6 show very closely the actual time of exposure of the plate at the respective distances in arc from the center, indicated by the figures of the upper line. In other words at a distance of 16' from the center, the time of exposure was 0.04; at 32' it was 1.76 and at 110' it was 85.00. The semi-diameter of the Sun on May 28, was nearly 15′ 47′′, that of the Moon at the same time was 15′ 58′′, nearly. From these figures it will be readily understood how the time of exposure was related to the corona and the limb of the black Moon in the short period of totality. It is also evident why the time of the total phase was so short which was a disadvantage, in view of the work, but also a small advantage in revealing the inner corona when the obscuration was greatest.

Mr. Burckhalter speaks confidently of the time of exposure in the different parts of the corona which was under control and says that they are not simply approximate, but they are very close to the values given, and certainly within one fortieth of the values named.

Astronomers who are practical photographers will certainly be interested in this new piece of apparatus, designed some time ago by Mr. Burckhalter but who has not before had opportunity to give it a trial in eclipse work.

Another feature of this eclipse of some interest was that of the shadow bands. As noticed in the article above referred to last month, care was taken at the station in Southern Pines, to observe this phenomenon and the results are given on page 303. In an article, elsewhere published in this number, by Professor M. Moye, of the University of Montpellier, France, interesting facts

about the same phenomenon appear. They are so different from those noted by the observers of the Carleton College party and others at the same station, that it has seemed desirable to call attention to these observations. Both seem to be definite, and to have been carefully made in all respects, but the differences of velocity, width of shadow and direction of motion are considerable. It might be possible to bring these observations into harmony if we knew more of the nature of this phenomenon and the circumstances of observation at the two stations which may differ in some important particulars.

Another point of some interest, which may be spoken of more fully later, is the relation of the form, and some other features of the corona, to the 11-year cycle of the sun spots. Some astronomers have thought that such a relation exists, and they have been studying total eclipse of recent date to ascertain, if possible, the evidence on which such a supposition rests. It is claimed that in or near the maximum part of the period, solar eclipses show a correspondingly large and active corona, as indicated by the number and length of his streamers, its rifts and its varied and complex structure. In the inner corona and about the polar regions in the eclipse of 1889 a most beautiful display, probably of electrical and magnetic lines of force were seen by many observers. Those who gave special attention to a visual study of the corona of the eclipse in May last, say that the two have points of resemblance in the particulars just mentioned. On the whole, the supposition is a reasonable one. If the corona is due to the condition of the photographic regions, we ought to expect changes in its visible structure when the solar surface is most active. Since this is especially true of the equatorial regions of the Sun as compared with those of the polar, at all times, it ought also to be true of the equatorial regions when the greatest differences of activity exist there. More will be said later of the work of professional astronomers when the results of the same are more definitely known.

This brief account should not close, for the present, without reference to the work of some of the amateurs. It would be profitable to say much of what was done by this large and enthusiastic class of observers who occupied many stations in the line of totality, and who obtained useful results by the aid of small instruments. The articles for the papers, the many photographs of the corona and the illustrated pamphlets that have come to hand plainly show this. One of the neatest of these pamphlets was by David E. Hudden of Alta, Iowa, which is a

fitting souvenir of his trip to Wadesboro, N. C. The illustrations of some of our plates were taken from this booklet; those showing Mr. Hadden at his 4-inch telescope, the location of the British Association Station and some observers with Professor Young in front of the temporary photographic house. The whole pamphlet consisting of a popular account of the eclipse is interesting reading, and the many photographs sent therewith are excellent.

Chas. P. Howard who observed in connection with the Trinity College party at Winston, N. C., has a good report of his observations and a drawing of the corona in the Trinity College Bulletin, No. 2, 1900. He says the conditions for work at Winston were favorable in a rare degree.

Professor C. M. Charroppin of St. Louis sent us very good photographs of the eclipse by small cameras. One in particular which showed streamers nearly three diameters of the Moon. In one of our plates his arrangement of a number of cameras is shown. Professor Charroppin is an excellent photographer. E. N. Fought, of the "Herald" Carlisle, Pa., who has written somewhat for this magazine, on popular themes, favored us with a full accout of the work of the Dickinson party which observed at Pungo, Virginia. A large Rowland concave grating was used in photographing the spectrum in the eclipse work of this party. We would speak of these and other parties from which notices. have come, but space is wanting for it at this time. Later we will give the results of many amateur who have reported contact observations at stations in, and outside of, the path of totality.

ON THE PROPAGATION OF THE TIDAL WAVE UPON THE TERRESTRIAL SPHEROID REGARDED AS SOLID AND COVERED BY OCEANS OF UNIFORM DEPTH.*

T. J. J. SEE.

FOR POPULAR ASTRONOMY.

The aim of this short paper is merely to draw attention to certain simple phenomena connected with the tide-wave. The oscillations of the particles of the sea are very imperfectly set forth in every work with which I am acquainted, and as many elementary works treat the subject in an erroneous manner, I have been

* Read before Section A, American Association for the Advancement of Science, New York, June 27, 1900.