ASTRONOMY AND METEOROLOGY. 393 



while the penumbras are cracked and gaped outward like old and wind-tossed 

 palm leaves. 



There is no certainty, therefore, that any but the principal spots on Mars 

 arc stationary. To reconcile the different drawings, it is quite necessary to 

 suppose that the numerous white patches about the poles succeed each other 

 rapidly, and therefore are more likely to be masses of storm clouds than in- 

 creasing and decreasing areas of snow. The least agitation of the atmosphere 

 makes the beautiful colors of the planet's disk grow pale and confused. The 

 general surface is a monotonous continent crossed by an equatorial zone of 

 red and temperate zones of blue, except in one place, where a large red island 

 is surrounded by a blue channel. Toward the edges of the disk the red spots 

 become yellowish, as if there were a martial atmosphere. 



NEW DETERMINATION OF THE SOT. AT?. PARALLAX. 



The following communication by Lieut. J. M. Gillis, has been officially 

 made to the Secretary of the Navy, under the date of Feb. 18, 1858: 



I have the honor to communicate to you the results of the observations 

 specially made by the United States Naval Astronomical Expedition to de- 

 termine the solar parallax the sun's distance from the earth. 



It will be remembered by the Department that Dr. Gerling an eminent 

 geometer of Germany suggested the practicability of determining this fun- 

 damental astronomical datum from observations of Venus near the inferior 

 conjunction, instead of awaiting the rare phenomenon of transits of the 

 planet across the sun's disk ; that an expedition to the southern hemisphere 

 was proposed to the Department by myself, for the purpose of making these 

 observations, which, in connection with similar observations to be made at 

 the Naval Observatory, would test the method; and that the earnest com- 

 mendation of the measure by physicists, both in Europe and this country, 

 induced Congress to authorize the expedition by special grants in the appro- 

 priation bills approved in 1848 and 1849. 



We were absent from the United States nearly three and a half years, and 

 the observations, constituting the more immediate object of the expedition, 

 extended through parts of each of the years from November, 1849, to Sep- 

 tember, 1852, inclusive. So many classes of observations were embraced in 

 the plan of operations adopted by the Department, that our small party was 

 almost constantly occupied in observatory duty proper, and it was not pos- 

 sible to prepare any of the data for the final computations until after the 

 return of the expedition to the United States. Then our first efforts were to 

 put in proper form for the computer all the observations of the planets Venus 

 and Mars, and the stars with which they had been compared. Whilst our 

 men of science had been unanimous in advocating the organization of an 

 expedition, because of the additional mass of important information certain 

 to be collected by it, there were some who entertained an opinion that the 

 method of determining the parallax proposed by Dr. Gerling would not afford 

 a result as reliable as had been derived from the transits of Venus in 1761 and 

 1769. For obvious reasons, therefore, it was proper that the discussion of the 

 results from our observations should be intrusted to an astronomer wholly 

 uncommitted as to the comparative merits of the two methods. 



Under the sanction of the Department, Dr. B. A. Gould, junior, of Cam- 

 bridge, Mass., was selected for the purpose; and the result obtained by him 

 for the Sun's Equatorial Horizontal Parallax is 8 /A 4950, or //> 0762 less 



