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TRANSITS OF MERCURY
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valuable information is afforded respecting the exact law of motion of the planet.

The first observation of a transit of Mercury was made by Gassendi on November 7, 1631. His observation is not, however, of any scientific value at the present time, owing to the imperfection of his instruments. A somewhat better but not good observation was made by Halley, of England, in 1677, during a visit to the island of St. Helena. Since that time the transits have been observed with a fair degree of regularity. The following table shows the transits that will be visible during the next fifty years, with the regions of the earth in which each may be seen:

1907, November 14, visible in Europe and eastern United States.
1914, November 7, visible in the same regions.
1924, May 7, the beginning will be visible on the Pacific coast, but the whole transit only on the Pacific Ocean and in eastern Asia.
1927, November 9, visible in Asia and eastern Europe.
1937, May 11, Mercury will graze the south limb of the sun. The phenomenon will be visible in Europe, but will occur before the sun rises in America.
1940, November 10, visible in the Western and Pacific States.
1953, November 14, visible throughout the United States.

Observations of transits of Mercury since 1677 have brought out one of the most perplexing facts of astron-

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