"The interest of this paper is much increased by the circumstance that no accurate experiments on the intensity and dip of the needle have heretofore been made in the United States, west of the Alleghany mountains.

"The Committee conclude their Report by recommending that Professor Locke's Communication be printed in the Society's Transactions."

"PETER S. DU PONCEAU,

R. M. PATTERSON,
J. SAXTON."

Dr. Patterson laid before the Society, copies of a Memorial presented to Congress by Dr. Henry Hall Sherwood, and of a Report thereon by the Committee on Naval Affairs of the Senate, in which are set forth Dr. Sherwood's "claims to have made new and important discoveries in magnetism generally, and more particularly in the magnetism of the earth; and to be the inventor of an instrument called the geometer, whereby, without the aid of the quadrant or sextant, or chronometer, and without taking a celestial observation, it is practicable and easy, at sea and on land, and in all weathers, to determine, merely by the dip of the needle, the variation of the needle, and the latitude and longitude of any place on the surface of the globe."

Dr. Patterson called the attention of the Society to some further extracts from the Report of the Naval Committee, in which it is stated that from the opinions obtained from scientific men, "as well as from their own examination, they are fully persuaded that the discoveries and invention of Dr. Sherwood are entitled to the most serious consideration of the public, and to the encouragement and patronage of Congress;" that they "regard them as highly interesting and important to the navigation and commerce of the United States, and as bidding fair to open a new era in the history of the science of magnetism." Of this Report 5000 additional copies were ordered to be printed by Congress.

Dr. Patterson remarked that the imposing circumstances under which Dr. Sherwood's extraordinary claims were brought forward, might make a brief review of them worthy of the Society's attention.

1. The first of Dr. Sherwood's asserted discoveries is the

communication of magnetism to a steel plate or ring, which he supposes others had failed to do. Dr. Patterson observed that, on the contrary, nothing is better known in experimental science than that magnetic polarity can be given to steel in any form, and with as many poles as the operator pleases. In illustration of this remark, he exhibited to the Society a steel plate, prepared some years ago by Mr. Saxton, who was then in London, according to an experiment first made by Chladni, on which polar lines were traced, so as to mark on one side the word 'magnet,' and on the other the date 24th of February, 1836;' the position of the lines being made apparent by strewing steel filings over the plate.

2. Dr. Sherwood asserts that, if a steel ring, marked in two opposite points, have magnetism communicated to it by passing it over a magnet from one of those points to the other, in a way which he describes, the magnetic poles will be found to reside, not in the marked points which he styles the poles of the ring, but in other points distant from them 23° 28', thus exhibiting a correspondence with the obliquity of the ecliptic. On this fact he founds his theory of the magnetism of the earth. Dr. Patterson mentioned that Mr. Saxton and himself had carefully repeated this experiment, and had found, without surprise, that the assertion of Dr. Sherwood was entirely erroneous. When the magnetism was communicated in the awkward manner used by Dr. Sherwood, the poles were not indeed at the points of the first and last contact of the magnet; but the deviation was irregular, was different at the different poles, and bore no relation to the obliquity of the ecliptic. When the magnetism was communicated to the ring by carefully setting two opposite points on the poles of a horse-shoe magnet, the magnetic poles of the ring coincided exactly with those points. This fact was shown in an experiment made before the society.

3. As to the hypothetical deductions of Dr. Sherwood," that the magnetic poles of the earth are 23° 28' from its poles, and of course within the polar circles," "that the magnetic and polar axes cross each other at the same angle of 23° 28'," "that the magnetic and terrestrial meridians of every place cross each other at angles dependent on the angles of the two

axes," and "that the line of no variation is a great circle of the earth, and is that magnetic meridian which, after cutting the magnetic pole, passes at the distance of 6° 28' from the pole of the earth," Dr. Patterson remarked that these notions were directly contradicted by well observed facts, that there are more than two magnetic poles, that the magnetic poles are not in the polar circles, that there are several lines of no variation, and that those lines are not great circles, but are altogether irregular in their course.

4. The practical applications of Dr. Sherwood's theory are announced in these terms: "With the correct dip given him, observed at a given time, he works out either or all of the following results: the variation of the needle, the distance of the circle of no variation from the place, and its angle with the meridian, and the latitude and the longitude. With the variation given him, in the same manner, he determines the dip and the other results. He must know, however, if the dip be given, whether the place of observation is east or west of the circle of no variation; and if the variation be given, whether it is north or south of the magnetic equator, and near the arctic or antarctic semicircle of no variation."

It is sufficient to remark, said Dr. Patterson, on this train of assertions, that they necessarily assume the truth, within the limits which are stated, of two positions; 1st, that the same dip will always correspond with the same variation, and 2d, that every place on the earth's surface has a different dip from all others, both of which are notoriously untrue. The various examples, contained in the Report, of calculations made from the single datum of the dip or the variation, and which give for results all the other particulars with an accuracy extending not to seconds merely, but to thirds, must be regarded as illusory.

Mr. Walker also made a verbal communication on the subject of Dr. Sherwood's alleged discoveries. He remarked that even admitting the correctness of the Doctor's hypothesis, as stated in his Memorial to Congress, still his method would be of no use for nautical or geographical purposes, for the following reasons:

1. The apparatus for determining the dip and variation of

the compass is more costly than a common sextant and mercurial horizon.

2. The observations of the dip and variation of the compass are more difficult to be made with accuracy than a common lunar observation.

3. The reduction of these magnetic observations, on the Doctor's hypothesis, would be more laborious than the working of a lunar observation.

4. Mr. Walker proceeded to show, in conformity with the remarks of Dr. Patterson, that Dr. Sherwood's assertion that he can determine the latitude and longitude from the dip alone, or from the variation alone, was contrary to the first principles of the geometry of position; since a point, in order to be determined in space, must be referred to three given 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 obser

vations.

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.

The following donations were received:

FOR THE LIBRARY.

Communication from Governor Marcy to the Legislature of New York, relative to the Geological Survey of the State, for the year 1837. With Plates. Albany, 1838.—From Messrs. L. Vanuxem and T. A. Conrad.

The same work.-From William Meredith, Esq.

The Light-Houses, Beacons, and Floating Lights of the United States, for 1838. Prepared by order of Stephen Pleasonton, Fifth Auditor. Washington, 1838.—From Stephen Pleasonton, Esq.

The American Journal of the Medical Sciences. Edited by Isaac Hays, M. D. No. XLIV, for August. Philadelphia, 1838.From the Editor.

The American Medical Library and Intelligencer. Edited by R. Dunglison, M. D. Vol. II. Nos. 8, 9, & 10. Philadelphia, 1838. From the Editor.