.bility to suppose that such a vast body of matter could be conglomerated into one homogeneous mass. Admitting, then, that the sun is made up of fluid portions of unequal density and of different radiating powers, it follows that currents will be established which will soon be regulated, in regard to their location and direction, by the rotation of the entire globe. These currents will certainly come in conflict with each other in the region of their common origin, and revolving storms, or eyclones, must be the result: At the same time, as we shall see in the sequel, there are at work other and more recondite agencies than a simp difference in density between the constituent portions of the solar mass- agencies whose effects are experienced, not only in the sun itself, but also on our earth, and probably throughout the system.

In addition to the observations which have been made upon individual spots, for the purpose of determining their general characteristics, motions, etc., other investigations have been conducted, the object of which was to determine whether the number of spots visible at any time was subject to law, and these investigations have led to a remarkable discovery. The astronomer, Schwabe, of Dessau, has been constantly engaged in this work from the year 1826 up to the present time, having examined the surface of the sun with his telescope almost every day during this long period of forty-five years. The tabulated results of the observations made by this persevering scientist point out the remarkable fact, that the number of spots visible from year to year changes its value through a well-defined period. Thus, in the years 1828, 1837, 1848, and 1860, the number of new groups or spots attained its maximum, while the minimum was reached in 1833, 1843, 1855, and 1867. We have here evident indications that the cause which produces the spots is not capricious in its operations, but that it is regular, and, therefore, as subject to law as the force of gravitation. itself. Professor Wolf, of Zurich, who has studied very carefully these observations of Schwabe, has come to the conclusion that the spot period is about 11 years, during which the number of new spots passes through its entire series of values from the minimum to the maximum, and back to the

minimum again; and it is worthy of notice, that in every case the progression from minimum to maximum is much more rapid than from maximum to minimum. Professor Wolf has also discovered that, in addition to the well-marked period above alluded to, there is also a smaller period, of about 73 months, which is very nearly the periodic time of the planet Venus, and there is reason to believe that a still longer period of 56 years exists.

The periodicity of the solar spots has a remarkable connection with that of another and totally distinct class of phenomena, viz., those of terestrial magnetism. It is well known that the magnetic needle, when freely suspended, and allowed to come to rest, points, approximately, north and south. But it is found that this position of the needle is by no means stationary. In fact, the needle oscillates during the day, about its mean position, owing to a tendercy on the part of that pole which is nearest the sun to direct itself toward that body, the extent of the vibration amounting to a quarter of a degree or more. This daily oscillation itself varies with the time of the year, while the mean position for the day is also undergoing change. There is a line (an irregular one) surrounding the earth, at every point of which the direction of the needle is truly north and south. This line, however, is not permanent, but slowly revolving around the earth, from east to west, at a rate which, if constantly maintained, would cause it to complete one revolution in about a thousand years. At all points east of this line the needle points to the west of the true north, while the reverse is true on the opposite side. These horizontal fluctuations of the needle are all regular and systematic in their character; the laws governing them have been, to a considerable extent, ascertained, and they can be more or less successfully predicted. But, besides these normal changes, the needle is subject to occasional great irregularities and fluctua tions. It may have been oscillating regularly for days and weeks together, when all once it will begin to vibrate rapidly and violently without any apparent cause; and what is to be particularly noticed is, that these sudden changes are not local in their character, but progress through large portions of the

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earth, and, in some instances, they have been observed at widely separated places at the same moment of time, indicating that some great disturbance has affected the magnetic condition of the entire globe. Such phenomena are appropriately designated magnetic storms. They have been made the subject of study by eminent physicists for many years, and it has been demonstrated that they are, like the solar spots, periodic in their character. And, wonderful to relate, the periods of the two phenomena are identical; they are the same in extent 11 years—and they are the same in point of time, that is, they attain their maxima and minima at the same time. Such a coincidence between two classes of phenomena, so apparently distinct from each other, is certainly very remarkable; but it goes further still. further still. It has been shown, by Carrington, Balfour, Stewart, and others, who were eye witnesses of the events they described, that sudden disturbances, taking place in the sun's surface, are attended instantaneously by magnetic storms on the earth a fact which, taken in connection with the perfect synchronism of their periods, points unmistakably to the existence of a physical relation between the two events, and shows that the phenomena of terrestrial magnetism are as dependent upon the action of solar forces as is the orbital motion of the earth upon the attractive power of the sun's mass. The explanation of this relation, the determination of the single cause to which both the sun-spots and magnetic storms are to be referred, must be left to further investigation.

We proceed now to the consideration of other and, perhaps, more interesting matters connected with the solar orb. During the total eclipse of the sun which occurred in the year 1842, the attention of astronomers was directed to the appearance of certain rose-colored protuberances which were visible around the obscured disk of the sun. These objects had been noticed previously, but they were explained away as being nothing more than clouds floating in the atmosphere of the moon, and no. further attention was paid to them. On the occasion referred to, however, the eclipse was watched by many of the most eminent astronomers of the day, all of whom paid special

attention to the phenomena presented by the prominences which were seen projecting outward from the edge of the solar disk. Much speculation was indulged in with regard to their nature and origin. The former view, that they existed in the atmosphere of the moon, could no longer be entertained, for it came to be the generally received opinion, that the moon was devoid of any such appendage as an atmosphere. Various other hypotheses were accordingly suggested. Some supposed them to be mountains in the sun; some held that they were solar clouds, maintained at an immense height above the surface of the sun self, while others looked upon them as flames, and, as is usual in such cases, there were some wise men who went so far as to deny their existence, asserting them to be nothing more nor less than optical illusions.

The eclipse of 1851 afforded astronómers another opportunity of viewing these singular objects, many excellent drawings of which were then made. The observations made on this occasion were sufficient to decide many of the questions which had risen respecting the prominences. Thus the exceedingly irregular and changing shapes of many of them precluded the idea of their being solar mountains. One of them in particular, likened by the Astronomer Royal of England to an Australian boomerang, projected vertically from the edge of the sun to a height of three minutes of arc (equivalent to at least 80,000 miles), and then curved off in a horizontal direction to at least as great a distance-a form altogether incompatible with that of any solid body. ssrs. Hinds and Dawes, in their description of this same prominence, as observed by them, state that it continued to be visible for some seconds after the reappearance of the sun, and the latter observes that he detected in the upper part of the prominence a flickering motion. Again, during the progress of the eclipse, the prominences first appeared on that side of the sun which was in advance of the moon; as the moon passed on it moved over and gradually concealed these prominences, while at the same time others came into view on the opposite side of the sun. This traversing of the prominences by the moon (a point which has been brought out more fully since the time of which

we are now speaking, shows clearly that they are not attached to the moon, neither are they optical illusions, but that they are true solar appendages of some sort or other.

The opinions formed in '51 were further confirmed by the observations made during the eclipse of 1860, on which occasion, in addition to the ordinary means of observation, the powers of photography were called into requisition by Mr. De La Rue, of England, and Fr. Secchi, the director of the observatory at Rome. Without entering into details, we shall briefly recapitulate the results at which these distinguished physicists arrived, as recorded by Secchi

1. The prominences are real phen nena appertaining to the sun.

2. They are collections of luminous matter of great brilliancy, and possessing remarkable photographic activity, so that many which could not be seen with the naked eye, or with the telescope, left their impressions upon the photographic plate.

3. In addition to the prominences which seem to be directly attached to the sun, there are others suspended in the atmosphere above.

4. Besides the prominences, there exists a zone of the samematerial enveloping the whole of the sun's globe. The promi nences spring from this envelope; they are masses which raise themselves above the general level, and sometimes become detached from it. Some of them resemble smoke from chimneys, or from the craters of volcanoes, which, after mounting upward to a certain elevation, is blown off horizontally by the currents of air.

5. The number of the prominences is very great, while the height to which they ascend is enormous, reaching in some instances to 160,000 miles, or twenty diameters of the earth.

Before the occurrence of the next great eclipse the spectroscope had been invented and brought to a considerable degree of perfection. In 1868, in India, and in 1869 in our own country, both years being favored with total solar eclipses, astronomers availed themselves of this wonderful instrument, and succeeded in obtaining a complete and satisfactory settle