Alexandria Gazette, Commercial And Political

From the N. Y. Mercantile Advertiser.

Solar Spots, in April and May, 1816.

SOL. the Sun, the most splendid of the celestial globes, diffuses light and heat through the whole planetary system. Many authors have written upon his nature and constitution. A catalogue of these heliographic books, was published at Helmstadt, in Germany, during 1753, by Nicholas Frobenius; but in 1768, Mich. Chr. Hanovius attempted in a formal dissertation, to demonstrate that the sun was not a body of fire.

Astronomers on beholding this grand luminary, are satisfied that he is not equally radiant in every part. His surface is occasionally beset with spots or clouds, of which the famous professor, Weidler, of Wittemberg, has exhibited an able summary. The usual facts and appearances of solar maculae, are these: to wit.

1. Occasionally on the disk of the sun are seen blackish spaces, of a round, oval, or irregular figure. They often have a dark nucleus, whose circumference is tinged with a red and blue color. They are called maculae or spots.

2. Frequently, as the French astronomers remarked, during the seventeenth century, there were none to be seen for days, months, and even years in succession. Picard, Hevelius, and Marian, distinguished themselves by the assiduity with which they pursued their investigation upon this subject.

3. The number visible at a time in the sun, varies: for sometimes there is but a single one: and then again, ten, twenty, thirty, or more, have been distinguished. Scheiner discovered on a certain occasion, fifty spots in sight at a time, on the Sun's disk.

4. Their apparent magnitude varies: they occupying at different times the hundredth, fiftieth, thirtieth, twentieth, and even a greater portion of the sun's diameter.

5. They usually make their appearance first near the easternmost margin of the sun, whence they pass in a curved line to the westernmost edge, and disappear. Near the summer and winter solstices, their line of motion is straight.

6. Near the extremities of the disk, they move more slowly; towards the centre their progress is faster.

7. Seen near the margin they seem smaller; while beheld in the middle of the disk they look larger.

8. Sometimes a single spot will divide into several; and then again several will coalesce into one.

9. Yet spots have been observed to show themselves first, in the middle of the sun, and then gradually to vanish or go out of sight.

10. The motion of the maculae on the hemisphere of the sun, which is turned toward our planet, the earth, lasts about fourteen days, and continues about as long on the opposite side. The period of their revolution, according to Du Hamel, is twenty seven days or thereabouts. Some of them have returned again and again--others, however, do not present themselves a second time, but melt away, or are dissipated while they are going round on the opposite hemisphere. De la Lande calculates the period of the sun's revolution on his own axis, to be 25 days and 10 hours.

11. Spots which have been seen from remote regions of the earth, have been referred to the same point of the sun's disk.

From these facts it may fairly be inferred that solar spots are opaque masses impenetrable by the sun's rays. Their position between the sun and us withholds a portion of his light; and during their continuance the earth receives a diminished share of its radiance. His diminution of solar influence must have as effect upon our planet and its atmosphere, rendering them both cooler than they otherwise would have been.

Our spring has been exceedingly backward and chilly; and is nearly six weeks less forward than common. Mr. Mitchell has shown, by several collections of facts, from year to year, the sensible operation that the vast masses of ice working to the southward, in the Atlantic ocean from Greenland, as far as the latitude of 43, have upon the atmosphere and temperature of the north eastern section of America. This very spring of 1816, as that gentleman observed, brings further confirmation, of the doctrine, that the chilliness of April, May and June may be owing, in a great degree, to the presence of such extensive fields and islands of ice in the Newfoundland station. We now endure that double operation of solar spots and Greenland cold.

Spots in the sun were observed in the year 1611, by Fabricius in East Friesland, Scheiner at Ingolstadt in Germany, and Galileo in Italy. They have since been very diligently watched and described by later astronomers. Those which obscured the disk of the sun in 1806, were carefully watched by the Rev. David Wiley of Georgetown (D. C.) and their descriptions recorded in the 10th vol. of the New-York Medical Repository, p. 180, and seq.

The method of observing them in the best manner, has been stated by Weidler, in his Helioscopia emendata et illustrata, to which the curious are referred.