however, was rendered to the enterprise in this country, except in the instance here referred to, in which the observations were conducted by Dr. Bache, at Philadelphia, by means of funds supplied by the members of the American Philosophical Society and the Topographical Bureau of the United States, and with instruments furnished by Girard College. This series of observations commenced in May, 1840, and, with short interruptions, terminated in June, 1845, thus furnishing a record extending over five years, for three or four months of which the observations were made bi-hourly, and for the remainder of the time hourly. A general reduction of these observations was published in 1847, by order of Congress, in three octavo volumes, with an atlas of diagrams. The records, however, contained facts of great interest, which, owing to the laborious duties of Professor Bache, could not then be deduced from them, and he has since renewed the investigation, with the aid of Mr. Schott, and the present paper gives an account of the first results which have thus been obtained.

To present the bearing of the interesting researches exhibited in this paper on the progress of science, it may be proper to state that the magnetic force of the earth is almost constantly disturbed, both in direction and intensity.

1. It is subject to a change which appears to complete its cycle in a large number of years, for the determination of which it is necessary to know the magnetic state of various places on the globe simultaneously at a given epoch, and again after the lapse of several years. 2. It is subjected to a change which is completed in the course of a year; and 3d, another which runs through its course in a single day.

Beside these regular disturbances, there is another series of variations, large in magnitude, denominated magnetic storms, which have been, until lately, considered as fitful, appearing to observe no law, but which were manifest over a considerable part of the earth's surface. These, however apparently irregular as to the individual instances, are in all probability, as has been shown by General Sabine, subject to a law of more frequency of occurrence in certain years.

The object of Professor Bache's paper is to investigate from the data furnished by the Girard observations, the law of recurrence of the latter disturbances. Since this has not as yet been accurately ascertained, and every independent series of observations when properly discussed is of great value in giving more precision to our

knowledge of one of the most remarkable classes of phenomena presented in the whole course of physical science, the results of this discussion cannot but be received with much interest by the scientific world.

As the magnetic needle, for example, may be considered as subjected at the same time to different forces, each tending to produce one of the variations we have mentioned, it becomes a subject of nice inquiry to eliminate the several effects, and to obtain the magnitude and period of each separately. In the case under consideration it was necessary to separate more especially the large apparently fitful variations from the regular daily ones. To effect this, the process proposed by Professor Peirce, of Cambridge, and founded on the doctrine of probabilities, was employed as a criterion in judging as to the magnitude of a disturbance which should be considered as belonging to the class under consideration, and it was finally concluded that all disturbances which exceeded 3'.64 of an arc were abnormal, and accordingly all observations differing by that amount or more from their mean monthly values were marked. Next, a new hourly mean was taken, omitting the values so marked, and each observation again examined in reference to deviations from this new mean, and so onthe last mean thus obtained for each hour during each month gave what was considered the normal daily curve.

From this it appears that the north end of the needle reaches its greatest eastern position between 7 and 8 o'clock in the forenoon, and its greatest western deviation about 1 o'clock in the afternoon.

The author next proceeds to discuss the large disturbances, and from these he deduces the fact that a principal maximum of disturbances occurs in October, a smaller one in April, and the two minima, nearly equal to each other, occur in the months of February and

June.

The diurnal variation arising from the large disturbances presents one maximum and one minimum; its most prominent feature is the easterly deflection, which occurs about a quarter after 8 o'clock p. m., at which hour the maximum deflection amounts to 32" of an arc; the great westerly deflection takes place at a quarter past 6 a. m., and on an average amounts to 14".

These variations are compared with deductions made from similar observations at Toronto, and are found to be the same in kind, but less in magnitude.

The whole discussion clearly indicates a law of recurrence in the frequency of the large disturbances, although the period over which the observations extend was not sufficient to determine the interval. The observations, however, indicate with great precision the time of the minimum, the rate of diminution as the disturbances diminish in approaching this period, and their increase as they recede from it. The minimum thus found, of frequency of large disturbances, occurred in August, 1843.

The establishment of the elements of a law of periodicity in relation to changes of the magnetic force which, from the time they were first noticed until within a few years past, were regarded as entirely irregular, is in its relation to terrestrial magnetism a fact of importance; but the value of this is highly increased when it is found that these disturbances are connected with changes in matter foreign to our earth. To realize this, we must refer to a series of persevering observations made day by day for thirty years on the spots of the sun, by an astronomer named Schwabe, in an obscure town of Germany. This devotion to an apparently unfertile field of inquiry was finally rewarded by the discovery that the spots on the sun's disc are subject to a regular law of recurrence, and that they pass through the phases of periods of greatest and least frequency in about eleven years; but strange to say, it was afterwards announced by General Sabine that the period of recurrence of large magnetic disturbances coincides. both in duration and its epoch of maximum with the period discovered by Schwabe in reference to the solar spots; that is, that at the period of greatest disturbances there occurs the maximum number of spots, and vice versa. The investigations of Professor Bache serve to establish this conclusion, and to furnish additional elements for a more accurate comparison. From these results it is clear that the sun exerts an influence on the magnetism of the earth which depends on the existing state of its own luminous atmosphere, affording another example to be added to other illustrations of the same truth, that scientific researches, if skilfully and perseveringly continued, will always lead to valuable results, and often to those which could not have been anticipated by any previous conceptions.

The volumes of records of the Girard observations, which present on casual examination immense series of tabulated figures in which no law or regularity is observable, when scientifically studied and properly interpreted, are thus found to yield truths of the highest

interest. Professor Bache proposes to continue his inquiries and extend his investigation to the influence of the moon and other agents on the magnetism of the earth. He has already finished a second paper on these discussions, and has a third in a state of considerable advancement. These will probably form a part of the twelfth volume of the Contributions.

The eleventh volume also contains a second series of the discussions of the physical observations made by Dr. Kane during his last voyage to the Arctic regions, the first part of which, or that relating to terrestrial magnetism, was published in the tenth volume of Contributions. This second part relates to meteorology, and was prepared for publication in the intervals of his official duties by Chas. A. Schott, esq., assistant in the United States Coast Survey, under the direction of Prof. Bache, and at the expense of the Smithsonian funds. This memoir not only forms an interesting and important addition to meteorology, which will tend to connect the name of our lamented countryman with this branch of science, but also furnishes a model for imitation, of the method in which observations of this character ought to be reduced and discussed in order that they may best subserve the advancement of science.

The following account of some of the points of the memoir and of the facts developed will probably be generally interesting and serve to illustrate its value:

The observations were made at Van Rensselaer harbor, on the western coast of Greenland, and extend over a period of two winters and a considerable part of two summers, during which the vessel was constantly frozen in the ice.

They show in a very striking manner the constant and laborious occupation of the little party in their lone abode, records having been made at every hour of the day and night during the whole period. It would be out of place in this report to give a full account of all the subjects discussed in this memoir, and I shall therefore only glance at a few of the most prominent points, referring to the paper itself for a full exposition of its more valuable contents. consists of three parts--the first is on temperature, the second on winds, the third on atmospheric pressure. The first part, viz. that on temperature, gives the observations for every hour, from which are deduced the diurnal and annual variations of the thermometer, the influence of the different winds on the temperature, and an

It

analysis of the recurrence of cold periods during the winter; tables deduced from the daily observations for ascertaining the corrections required to be applied to observations made only once or twice a day in order to obtain the mean temperature of places within the arctic circle; and, finally, observations to determine the diminution of temperature with an increase of elevation.

Beside the corrected records of the motion of the air, the second part of the memoir contains the resultant direction, the average force, the mean velocity, the quantity, the frequency, and the duration of the winds. The third part contains not only the record of the pressure, but also a comparison of the mercurial and aneroid barometers, the diurnal and annual variation, the regular fluctuations of the monthly and annual extremes of pressure.

The expedition was supplied with thirty-six mercurial thermometers, four maximum and minimum thermometers, twenty-four spirit thermometers of different sizes, including two standards and a register thermometer of thirty-six inches in length. A laborious series of the different readings of these instruments, particularly at low temperatures, was made, from which have been deduced corrections to be applied to the records prepared for publication. The differences exhibited by the spirit thermometers at low temperatures was referred to the unequal contraction of colored alcohol not chemically pure. This liquid, when exposed to a great degree of cold, appeared to change its condition, the coloring matter being deposited on the sides of the tube. The lowest temperature observed during the first winter, 1853–54, was, February 6, —66°.4; and during the second winter, 1854-55, occurred, January 8, -65 .5.

The highest temperature observed was July 23, 1854, +51°, giving an absolute difference of 117°.4. The diurnal maximum or highest temperature of the day occurred in October and November, about one hour before noon, and in April and May, three hours after noon.

In the months of October, November, and December there are two points of low temperature each day-one at 6 a. m., and the other at about 9 p. m.; during the remaining months of the year there is one minimum during the twenty-four hours, which occurs at 1 a. m.

It was a fortunate circumstance that the observations extended over two winters, and thus gave a more exact mean for that season. The warmest month is July, the coldest March; the temperature of December, however, does not differ much from the latter.

The