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Angle, from N.Jfirst contact, 88° towards the W.
point, of last contact, 94° towards the E.
Angle, from Jfirst contact, 140° towards the W.
Vertex, of last contact, 38° towards the E.
Position west of Puerto del Inferno (Spain).
Long. 1° 43′ W., Lat. 38° 38′ N.

Local Mean Times.

for direct
image.

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The accompanying map of the line of totality will show the parts of Spain, Portugal, Algeria and Tunis from which this eclipse can be observed. It will be seen that the track, after leaving Spain near Alicante, crosses the Mediterranean and enters Africa close to Algiers.

We may be perfectly certain that the astronomers of the United States and France will man the beginning and the end of the line quite efficiently. It is clear, therefore, that the attention of British astronomers with serious work to do will be directed to the observing stations in Spain and Portugal.

The weather chances were stated by Professor Arcimis in a former number of Nature,* and may be considered excellent.

There are many branches of work, such as securing photographs of the corona, in which amateurs may do good service. For them the well-found steamers leaving Marseilles may make the coast near Algiers more convenient.-Nature, Dec. 28, 1899. * Vol. lix. p. 439.

ORIGIN OF THE LUNAR FORMATIONS.*

Various theories have been advanced at different times to explain the origin of the lunar craters, but the chief difficulty that astronomers have heretofore met has been to account for the gigantic scale upon which they are formed. In the series of experiments presently to be described, artificial craters have been constructed resembling those found at present upon the Moon. Since in the earlier experiments no recourse is had to capillary action, or to the explosion of gases, there seems to be no natural limit set to the size of the formations that may be produced by this method, either naturally or artificially. In the explosive experiments described later other features are illustrated. I should state that this investigation was suggested by a letter from Mr. J. B. Hannay, published in Nature, 1892, Vol. XLVII, p. 7. In it he describes some minute craterlets naturally produced in solidifying iron slag It seemed to me worth while to repeat these experiments, and to obtain if possible some substance more readily manipulated than melted iron. The substance which I found best suited to the purpose was paraffine. This material melts at so low a temperature that it can be readily handled in the viscous form, while at the same time it becomes quite hard and firm at ordinary temperatures. Like the materials composing the crust of the Earth, it contracts on solidifying, the change in volume in both cases being rather large.

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The paraffine was melted in an enamelled ware pan, measuring three and a half inches deep by eight in diameter, over a small spirit lamp. By employing a small source of heat the paraffine

From Vol. 32, pt. 2 of the Annals of Harvard College Observatory, by William H. Pickering.

was melted locally above the flame, and soon formed a little hole in the surface crust measuring about one quarter of an inch in diameter. That portion of the liquid in contact with the bottom of the pan was at a much higher temperature than that above it, and was forced upwards by the heat, rapidly enlarging. the hole formed in the crust above it. The hole retained its circular or elliptical form, and continued to enlarge as long as the hot liquid was brought in contact with it. As soon as it had reached a convenient size the lamp was extinguished, and the cooling process begun. As the lower regions of the paraffine cooled they contracted, and the liquid surface dropped, leaving a smoothly cut elliptical pit (Figure 14)*. The sides were at first quite shelving, but by reheating the fluid once or twice they became steeper, and even overhung in some places. Probably a rapid cooling at the surface, and a more rapid contraction of the fluid, obtained by using a larger reservoir, would accomplish the same result. If the contraction is allowed to proceed too far, however, the floor of the crater pit becomes concave, and may even be broken through by the pressure of the atmosphere.

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In Mr. Hannay's letter he refers to the former very powerful influence of the tides upon the liquids contained within, and upon the surface of the Moon. This tidal action was imitated by inserting a brass tube one inch in diameter and twelve inches long in the paraffine when it was first melted. The tube was fitted with a wooden piston packed loosely with cotton flannel. By . working this piston up and down, the melted pariffine could be made alternately to rise and fall inside the craters formed by it, and the cooling process could be hastened when desired by blow

* Number of Figure in Vol. 32, pt. 2, H. C. O. Annals.

ing upon the liquid surface. Craters (Figures 15 and 16) were formed in the same manner as the first one, excepting that after extinguishing the lamp the tidal action was brought into play, alternately pumping the liquid up to the rim of the crater, where it partially solidified, leaving a little ring of solid parffine, and then drawing it down again into the interior, where it soon partly remelted, preparatory to a renewed elevation. This tidal action was continued until the fluid became quite viscous, solidifying into little hills and ridges inside the crater, and later as the hardening surface was dragged out of shape by the pumping of the liquid below it, little cracks were formed around the edges and across the bottom of the crater, like the rills seen in similar situations upon the Moon.

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If now, we raise the piston high enough, and wait for air to get underneath it, we may force this down into the melted paraffine. The result is an explosion, in which the paraffine may shoot up several feet in the air. If care is taken, however, the jets may be confined to the height of a few inches. A cone is soon formed (Figure 17), and the liquid paraffine trickles down the slopes in miniature lava streams. As the cooling process goes on the paraffine comes out in bubbles, like soap suds, which break and rapidly build up the cone. If the process is continued further, partially solid lumps of paraffine are projected into the air, falling down upon the outer slopes of the cone. The crater now gradually narrows, and if care is not taken will soon become clogged. With care many well known volcanic phenomena may be repeated, such, for instance, as the shifting of crater to one side, and the formation of a succession of crater rings and semi-circles. Also the bursting out of new craters near the base of the original

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