surfaces. If one of them is the surface of the spheroid as in geography, then the point must be referred to two other given surfaces; whereas, by the dip alone, or the variation of the compass alone, a point can only be referred to one of these two surfaces, and the resulting locus is a line and not a point. Hence, if latitude and longitude are determined by magnetic observations, it must be by both the dip and variation. Dr. Sherwood's method, therefore, could be of no use for nautical purposes, from the impossibility of observing the variation of the compass at sea with any tolerable degree of accuracy.

5. Dr. Sherwood's assertion that the magnetic method. could be used in cloudy weather is inaccurate; since the variation of the compass cannot be ascertained without astronomical observations.

6. Restricting then the use of magnetic observations to those made on land in fair weather, still, owing to local perturbations, the probable discrepancy of the mean of many observations at one place from the theoretic dip and variation, may, at a low estimate, be assumed to be ten minutes of space, and, as the resulting errors of latitude are of the same order, we should have ten miles for its probable error, which is twenty times that of a common sextant and mercurial horizon.

7. Owing to the proximity of the north pole to Dr. Sherwood's assumed magnetic pole, the probable error in the resulting longitude would far exceed that of the dip and variation themselves, and would amount to forty miles on the average, and between the tropics, near the line of greatest variation, to several degrees; whereas it is well known that by the lunar method, the probable error in longitude is less than six miles, and may be reduced to four by means of half a dozen observed eclipses of Jupiter's first satellite.

Mr. Walker concluded by remarking that although, in stating the practical objections to the method, he had taken Dr. Sherwood's postulates for granted, yet he considered every one of them as contrary to facts, observation, and experience.

Dr. Bache announced the death of Charles Maurice Talleyrand, Prince of Benevento, a member of the Society, who died on the 17th of May, 1838, aged 83..

Stated Meeting, August 17.

Present, eighteen members.

Mr. DU PONCEAU, President, in the Chair.

On motion of Dr. Patterson, a Committee was appointed to observe the eclipse of the sun of the 18th of September next. Committee, Dr. Patterson, Mr. Walker, Mr. Paine, and Captain Talcott.

2

Mr. Du PONCEAU, President, in the Chair.

The following donations were received;

FOR THE CABINET.

A mummy of the Ibis, in an earthen jar, taken from one of the catacombs of Egypt. From Lieut. P. Drayton, U. S. Navy. Four small models of human mummies; two of wood, and two of baked clay. From the same.

Several suites of minerals, comprising 33 specimens. Nos. 1 to 18,

rocks and ores from the Island of Cuba; Nos. 19 to 31, minerals from the mineral region of Missouri; No. 32, sulphuret of copper, from Flemington, N. J., No. 33, bituminous coal, from the banks of the Black Warrior River, Alabama.-From Mr. Thomas G. Clemson.

The Committee on the solar eclipse of the 18th of September made a Report in part, comprising the Observations made at Philadelphia, the principal results of which are as follows:

The observations made at Philadelphia are fifteen in number. A list of observers, telescopes, &c., is given in the following table. The correction in the third column is to be added algebraically to the latitude of the place of observation, to obtain that of the State House, +399 56′ 58′′. The correction in the fourth column is likewise to be added to the local longitude in time, to obtain that of the State House,-5h 0m 39.2s.