out going into details of the experiment the results will be tabu lated, Actual diam. as seen at 10 in. Apparent diam. at 200 yds. Apparent diam, Apparent diam. Carbon points, of an inch, the diam. moon's disk, 3 diam. do.do. -31 diam. do.do If then the apparent diameter of a luminous meteor at a given distance is to be accepted as a guide for calculating the real size of these bodies the Charcoal* points would be 80 feet in diam. instead of of an inch. It is not in place to enter into any explanation of these deceptive appearances, for they are well known facts, and were tried in the present form only to give precision to the criticism on the supposed size of these bodies. Comments on them are also unnecessary, as they speak for themselves. But to return to the two meteorites under review. That of Wilton was estimated by Mr. Edward C. Herrick, (Am. Journ. of Science, vol. xxxvii, p. 130) to be about 150 feet in diameter. It appeared to increase gradually in size until just before the explosion, when it was at its largest apparent magnitude of 4th the moon's disk-exploded 25° to 30° above the horizon with a heavy report, that was heard about 30 seconds after the explosion was seen. One or more of the obervers saw luminous fragments descend toward the ground. When it exploded, it was three or four miles above the surface of the earth; immediately after the explosion, it was no longer visible. The large size of the body is made out of the fact of its appearing one-fourth the apparent disk of the moon at about six miles distant. After the experiments just recorded, and easy of repetition, the uncertainty of such a conclusion must be evident; and it is insisted on as a fact easy of demonstration, that a body in a state of incandescence, (as the ferruginous portions of a stony meteorite,) might exhibit the apparent diameter of the Wilton meteorite at six miles distance, and not be more than a few inches or a foot or two in diameter according to the intensity of the incandescence.† Besides, if that body was so large, where did it go to after throwing off the supposed small fragments? The fragments were * Estimate made according to a table given by Prof. Olmsted (Am. Journal of Science, vol. xxvi, p. 155) for estimating the diameter of meteors on comparison with the moon. It ought however to be stated, that in the paper above referred to, Mr. Herrick expressly mentioned this and other sources of fallacy, endeavored as far as practicable to guard against them, and gave his final careful result as necessarily open to some uncertainty.—EDS. seen to fall, but the great ignited mass suddenly disappeared, at 30° above the horizon, four miles from the earth, when it could not have had less than six or seven hundred miles of atmosphere to traverse, before it reached the limit of that medium; it has already acquired a state of ignition in its passage through the air prior to the explosion, and should have retained its luminous appearence consequent thereupon, at least while remaining in the atmosphere but as this was not the case, and a sudden disappearance of the entire body took place in the very lowest portions of the atmosphere, and descending luminous fragments were seen, the natural conclusion appears to be, that the whole meteorite was contained in the fragments that fell. As to the Weston meteorite, it is stated that its direction was nearly parallel to the surface of the earth at an elevation of about 18 miles; was one mile farther when it exploded; the length of its path from the time it was seen until it exploded was at least 107 miles; duration of flight estimated at about 30 seconds, and its relative velocity three and a half miles a second; it exploded; three heavy reports were heard; the meteorite disappeared at the time of the explosion. As to the value of the data upon which its size was estimated, the same objection is urged as in the case of the Wilton meteorite; and it is hazarding nothing to state that the apparent size may have been due to an incandescent body a foot or two in diameter. Also, with reference to its disappearance, there is the same inexplicable mystery. It is supposed from its enormous size that but minute fragments of it fell; yet it disappeared at the time that this took place, which it is supposed occurred 19 miles above the earth, (an estimate doubtless too great when we consider the heavy reports). Accepting this elevation, what do we have? A body one mile and a half in diameter in a state of incandescence, passing in a curve almost parallel to the earth, and while in the very densest stratum of air that it reaches with a vigorous reaction between the atmosphere and its surface, and a dense body of air in front of it, is totally eclipsed; while, if it had a direction only tangential to the earth, instead of nearly parallel, it would at the height of 19 miles have had upwards of 500 miles of air of variable density to traverse, which at the relative velocity of 3 miles a second (that must have been constantly diminishing by the resistance) would have taken about 143 seconds. It seems most probable that if this body was such an enormous one, that it should have been seen for more than ten minutes after the explosion, for the reasons above stated. The fact of its disappearance at the time of the explosion, is strong proof that the mass itself was broken to fragments, and that these fragments fell to the earth;-assuring us that the meteorite was not the huge body represented, but simply one of those irregular stony fragments which, by explosion from heat and great friction against the atmosphere, become shattered. I say irregular, because we have strong evidence of this irregularity in its motion, which was "scolloping," a motion frequently observed in meteorites, and doubtless due to the resistance of the atmosphere upon the irregular mass, for a spherical body passing through a resisting medium at great velocity would not show this. In fact, if almost any of the specimens of meteorites in our cabinets were discharged from a cannon, even in their limited flight the scolloping motion would be seen. This then will conclude what I have to say in contradiction to the supposition of large solid cosmical bodies passing through the atmosphere, and dropping small portions of their mass. The contradiction is seen to be based; first, upon the fact that no meteorite is known of any very great size, none larger than the granite balls to be found at the Dardanelles along side of the pieces of ordnance from which they are discharged; secondly, on the fallacy of estimating the actual size of these bodies from their apparent size; and lastly from its being opposed to all the laws of chance that these bodies should have been passing through an atmosphere for ages and none have yet encountered the body of the earth. To sum up the theory of the lunar origin of meteorites, it may be stated-That the moon is the only large body in space of which we have any knowledge, possessing the requisite conditions demanded by the physical and chemical properties of meteorites; and that they have been thrown off from that body by volcanic action, (doubtless long since extinct,) and, encountering no gaseous medium of resistance, reached such a distance as that the moon exercised no longer a preponderating attraction-the detached fragment, possessing an orbital motion and an orbital velocity, which it had in common with all parts of the moon, but now more or less modified by the projectile force and new condition of attraction in which it was placed with reference to the earth, acquired an independent orbit more or less elliptical. This orbit, necessarily subject to great disturbing influences may sooner or later cross our atmosphere and be intercepted by the body of the globe. In concluding this lengthy examination, I must say that a discussion of the phenomena accompanying the falling of meteorites has been avoided, as well as many points connected with their history. This has been done from its having no immediate connection with the object of this memoir, which is intended simply to present to the Association some new views, and many old views in a new light, so as to awaken attention to the study of this most interesting class of bodies. ART. XXXIV. On the Variable Star Algol, or B Persei; by FR. ARGELANDER.* ALGOL, or B Persei, is unquestionably one of the most remarkable of all the variable stars, on account of the shortness of its period, in general, and especially the short time during which it continues at its minimum,-on account of the comparative precision with which this minimum may be determined,-and the regularity with which the star goes through its period. This regularity is so great that Wurm, even in the year 1819, that is to say, thirty-six years after Goodricke had discovered the periodicity of the variation of light in Algol, was able to represent all the observations by a uniform period, and did not venture to decide whether this period had become longer or shorter.† Nevertheless, the values of the duration of a period computed by himself at various epochs, indicate the former of these alternatives. From the earlier observations, comprising a series of 16 months, he found the period to be 2d 20h 48m 59s; after sixteen years of additional observations, he diminished the time by 0s-3; and redetermined it after 36 years as 2d 20h 48m 588-5. The diminution of the time indicated by these computations has been put beyond all doubt by modern observations, which have also shown that the amount of this diminution is not proportional to the time, but is continually growing larger and larger. A collation of the duration of the period, as obtained by combining the nearly contemporaneous observations and discussing these series according to the method of least squares, will show this very distinctly. If we assume as the principal epoch, that of the minimum which occured 1800, January 2, morning, Paris civil time, the first column of the following table of periods gives the number completed since this principal epoch; the second, the time; the third, the duration of the period which holds for this time, accompanied by the probable uncertainty of this latter determination. A glance at this table shows immediately that the several observations can be represented neither by a uniform nor by a uniformly *Copied from the Astronomical Journal, No. 80, January 1855. diminishing length of period. They might, however, be represented by having regard to the third and fourth power of the time; or, still better, by introducing a correction to a uniform period, which should progress according to sines and cosines in such a way that the pth minimum after the epoch E would be given by the formula, E+ ap+b sin (np + B) + c sin (2np + C) + . . . . . But the endeavor to develop the constants, even taking account of the first term only in the series of sines, proves fruitless, owing to the insufficiency of the data; of which, indeed, we have a tolerable number for the last century, but which since then are so scarce, that for the first forty years of the present century I am only aware of 19 observed minima. In the last few years certainly the attention of astronomers has been again more directed to this remarkable phenomenon; but if we are soon to arrive at an accurate knowledge of the phenomenon itself, and of the rules according to which the period varies, the number of observers must be very considerably increased. Out of the 127 or 128 minima which occur in a year, there are scarcely 40 for which the requisite darkness, and a sufficient altitude of the star above the horizon, permit a trustworthy observation. Then deducting, not only the many days which are overcast, but those also on which flying clouds or mist disturb the observation, as well as those on which other pressing avocations prevent the astronomer from devoting his attention to the phenomenon, this number will be extraordinarily diminished. I have myself not yet succeeded in observing more than 8 minima in any one year, and then only in the year 1840, in which no more extended series of observations demanded my time. Under these circumstances, I take the liberty of earnestly entreating American astronomers to give their attention to this interesting phenomenon. Certainly some sacrifices are requisite for this, inasmuch as a complete observation demands not less than an hour and a half, during which the brilliancy of this star must be compared with that of others every 6m or 8m. For comparison-stars I use & and Persei, and a and B Trianguli. The star o Persei indeed is itself somewhat variable, but its period is longer, and it is especially favorable on account of its proximity to Algol, and because it is very nearly equal to this star when at its minimum. In a comparison of Algol with g, the little variations from uniformity in the transparency of the air, which always exist to a greater or less degree, will exert the smallest possible influence. Concerning the manner in which the comparative brilliancy of stars is to be observed without the aid of instruments, I have spoken in detail in another place ;* and will here only briefly re * Schumacher's Jahrbuch für 1844, p. 191 et ff. SECOND SERIES, Vol. XIX, No. 57.-May, 1855. 44 |