between the exterior and interior walls of Archimedes in the west. At both sides of the same there are noticeable rifts or ravines of considerable depth. SCHMIDT has no indication of this.

19. Upon SCHMIDT's chart this annular ridge is shown in the shape of a triangle. On I it is nearer like an oval lying in the direction of the meridian. Position angle and distance of the centres do not agree with sufficient accuracy.

20. This object seems to represent on I a crater-like depression but does not appear as such on SCHMIDT's repre

sentation.

21. On II there is seen at this point something that looks like a sort of a crater-pit of small size, but this object is just as likely to be a defect in the photographic plate.

22. This crater designated by SCHMIDT as C shows upon I an elevated appendage or buttress on the east towards the mountain E, and on II it shows to the north and almost adjoining it a shallow pit. These are not given by SCHMIDT.

23. This crater which SCHMIDT refers to as d, appears on I as a bright spot, but upon II as a real crater. The difference in distance between I and II is accounted for by the effect of libration. It might be presumed, judging from the diverse character as indicated by the photographic plates, that only the eastern wall of this crater is of a precipituous nature; while the western wall has a more gentle decline, which would throw a deep easterly shadow only at a lower position of the sun.

Mountain E.-This is interesting on account of the difference in shape on I and II. From it a long ridge reaches toward the southwest, which does not, however, end off as uniformly as SCHMIDT has it. Particularly interesting is the dark crossing of the same, shown on both drawings east of the crater d.

Concerning the interior of Archimedes it is shown that both photographs do not at all lend it the appearance of the "mirrorlike smoothness" of MADLER'S plain. In considering its numerous and diverse photographic details, it is of course to be observed that we are not able to separate those that are due to the inequalities of the bottom, from those that find their origin in faults of the plate and in the finer gradations of the sensitive film, so long as there are not at least two consecutively taken plates on hand for comparison. For this reason a discussion of the interior details of Archimedes must here be omitted entirely. It may only be mentioned that the well known lighter zones of the floor are quite

visible, but that of the finer craters, shown by SCHMIDT and others, nothing is discernible in the interior.

The whole comparison of these photographic representations with SCHMIDT's chart confirms again the excellence of the latter, but it shows too, that it may be improved upon.

It has also been of great interest to me to compare I and II under the same conditions of light with a view through the 6-inch STEINHEIL refractor of the Prague Observatory. II was compared on the 31st of March of this year, at 161⁄2" Prague mean time, I on April 17th, this year, at 81⁄2" Prague mean time with the celestial object. Although at both times the air was rather unsteady and not very clear, so that a magnifying power of only 150 seemed advisable, still it was readily proven to me that the photograph did not represent everything visible. For instance, clear and easily discernible tracings of terraces, on a brightly illuminated background were lost entirely, while in the lesser shaded parts a plentiful and just as easily distinguished detail was lacking altogether. It is possible to explain this only by assuming that the adopted mean period of exposure for the plate, which would furnish the best average picture, over-exposes the bright walls of Archimedes, and that thus the dark terrace lines thereon are obliterated, as a result of the effect of diffraction of the surrounding light, (compare the photographic representation of a narrow lightning-rod on a background of light clouds, which by exceeding a certain exposure will disappear entirely from the picture) and, on the other hand, shaded portions of the wall are under-exposed in the same manner. It must also be mentioned here that on the 17th of April of this year the crater d showed in its interior another shadow, whereas the same is entirely lacking on I. In addition to all this we must admit that numerous photographic details were not discernible with the telescope.

From the foregoing the conclusion is justified that photographic representations of the moon, as constantly improved upon and now approaching a degree of completeness never before attempted, as at the Lick Observatory, furnish a most valuable aid to optical observation, and will, considering the diversity in the chemical and optical albedo of the lunar surface, become the means of materially supplementing it. But it is to be remembered that one photograph alone will not give us an absolutely true representation of the moon, meaning a representation of everything visible; for with a certain period of exposure some parts will be sure

to be over and others under-exposed. It is only by taking a series of consecutive photographs of varying exposures, which should be confined rather to very small lunar areas, that we can finally hope to obtain a copy true to nature. In the same manner in which we succeed in photographing the dark solar spots on the bright face of the sun, we should also be enabled to obtain the dark terraced lines on the lighter walls, heretofore referred to, or the fine black rills surrounded by bright light, if the exposure of the plate be properly reduced. The final decision in this matter, however, will depend upon experiment. Although a photographic representation of the moon, in spite of the most excellent results of the Lick Observatory, leaves much to be desired in point of strength and clearness, as particularly apparent in studying the greater enlargements, it yet furnishes us a wonderfully beautiful relief of considerable expanse, which can never be retained and depicted with equal truth to nature by the most skillful draughtsman, on account of the great mass of visible objects and the rapid change of lunar shadows; and at the same time it gives an astonishingly accurate detail of individual portions, which for the control and revision of present lunar charts becomes of the utmost value to the selenographer.

PRAGUE, July 6th, 1891.

NOTE TO PROF. WEINER'S PAPER, BY EDWARD S. HOLDEN.

This is not the place to say how great an impulse has been given to the study of the moon by the investigations which Professor WEINEK has undertaken upon the Lick Observatory negatives. I desire, however, to say one word, in addition to what has already been said, upon the very important matter of reproducing the negatives, or drawings from the negatives, so that they can be published in large editions. This matter has engaged the attention of Professor WEINEK and myself for about two years. It is comparatively easy to find new features, and old features in new relations, upon our negatives of the moon; and it is easy to show these to any one who can study the original negatives or glass copies of them. It is, however, extremely difficult to reproduce the negatives in a large number of copies, so that any reader can follow a description. The most satisfactory method theoreti cally is to enlarge the original negatives by photography and to make silver prints from the enlarged negatives. This method has not been practicable for various reasons. It is very difficult,

for example, to obtain 1000 silver prints from a professional photographer which shall all be satisfactory. We have therefore tried various photo-mechanical, lithographic and other means of reproducing either the original plates, or enlargements from them. A specimen of the most careful lithographic work is given in the present paper. The best phototype reproduction which I have been able to obtain is given in the Century Magazine for July, 1891. No one of these plates does justice to the original from which it was copied-neither to the original negative nor to Professor WEINEK's exquisite drawings. And everything hitherto published must be regarded as tentative only.

We are, however, now in a position, to reproduce such originals in an adequate and entirely satisfactory manner.

Through the interest of Professor WEINEK and by the kindness of the Chief of the Imperial Institute of Military Geography, of Vienna, the Institute has consented to reproduce the drawings by heliogravure. Some specimens have already been received. and they show conclusively that the question of reproducing such work is solved. It is hoped to go on with these studies of the moon as rapidly as possible through the co-operation of Professor WEINEK and the Lick Observatory.

MOUNT HAMILTON, October 1, 1891.

ESTRELLAS FUGACES, BÓLIDOS Y AEROLITOS, ESTUDIO POR EL DR. JESUS MUÑOZ TÉBAR, (Caracas, 1891, 8vo, pp. 27.) [Abstract by the Author.]*

An essay presented by the author to the. Astronomical Society of the Pacific, as a membership contribution.

64

The essay begins by a succinct historical description, which, brief as it is, touches every important point studied and meditated upon during the present century concerning shooting stars, bolides and aerolites, and eventually lands on the explanation of the present cometary theory.

"Then it goes on exposing the principal incidents which have been observed in connection with the appearance of said meteors, and presents a series of very grave objections against the present

* Dr. TÉEAR has printed in Caracas, under the date of August 25, 1891, a pamphlet in the Spanish language with the above title. On page 2 of the pamphlet is an abstract in English which is here reprinted.

theory, objections based upon those observations and upon several scientific principles.

"After some very interesting considerations on the subject and a number of remarkable quotations, it concludes by proposing an entirely new theory for the explanation of these phe

nomena.

"According to the author the shooting stars are ball lightnings which abound in the upper regions of the atmosphere and under certain conditions their number all over one and the same region is so considerable, as to present the appearance of a shower. When these lightnings are formed in the lower regions of the atmosphere or in the case of their descending far down in the same, they originate the so-called bolides; and when the ball lightning darts through a cloud or through air impregnated with substances lifted up from the surface of the soil and scattered in the atmosphere through cyclones and hurricanes or volcanic eruptions, their effect is to unite all those substances into one single mass, thus forming the meteorite or aerolite.

"Ball lightnings and rains of ball lightnings are not of frequent occurrence in the atmospheric strata immediately above the surface of the earth, still there are instances of both kinds of phenomena."

BESTIMMUNG VON PARALLAXEN DURCH REGISTRIR-BEOBACHTUNGEN AM MERIDIANKREISE, VON DR. J. C. KAPTEYN.

BY PROFESSOR LEWIS Boss.*

A more exact knowledge of the sun's motion in space is a pressing requirement in preparing the way for the stellar astronomy of the future. Up to the present time all our attempts to regard the stars in a comprehensive way, as situated in space of three dimensions, have been either rudely tentative, or merely speculative. To some extent this must continue to be the position of generalization in stellar astronomy for some time to come. Yet it is plain to be seen that stellar astronomy in its true geometrical relations is gradually advancing in importance with sure steps and continuously, toward the point when it must become the most fruitful as well as the most imposing object of research

* Director of the Dudley Observatory, Albany, New York.