Imagini ale paginilor
PDF
ePub

The first column of figures under each year gives the mean percentage of cloudiness for the entire month of observation for the sky in general, as seen by the observer; the second column gives the mean percentage in the immediate vicinity of the Sun. The last section gives the means of the three years. Two facts are very evident as the result of these observations: (1) The three years each give the same result and therefore this must be founded upon a definite meteorological phenomenon pertaining to that region and season of the year. (2) The general fact is that the eclipse track region in the states of Georgia and Alabama is decidedly less cloudy than in the other states which are nearer the ocean areas, and which lie at lower levels. The conclusion follows that the chances of fair weather are better for eclipse parties locating on the highland of the southern portions of the Appalachian Mountains than in the lower districts nearer the Atlantic Ocean and the Gulf of Mexico. Of course this mean result is no guarantee that such local cyclonic conditions will not prevail on the morning of May 28, 1900, as to entirely modify this calculation, but the indications are that it will be at least twice as safe to locate there, as near the coast line.

A more complete report is soon to be issued by the Weather Bureau, which will contain other useful information for eclipse observers, such as the approximate longitude, latitude, altitude, hotel accommodations, drift of smoke, and easily accessible heights, for the towns which are located quite near the central line of the eclipse track. It will also contain a map of the southern states, with the boundaries of the eclipse track marked upon it, the location of the towns, the topography, and the available railway transportation lines.

U. S. WEATHER BUREAU,

Washington, D. C.

THE NOVEMBER METEORS OF 1899.'

THE predicted time of maximum of the November meteors is November 15, 1899, at 18h Greenwich Mean Time. As a similar shower may not occur again for thirty years, no pains should be spared to secure the best possible observations. The most useful observations that can be made by amateurs are those which will serve to determine the number of meteors visible per hour throughout the 1 Harvard College Observatory Circular No. 45.

entire duration of the shower. Circular No. 31 was accordingly distributed last year, and numerous valuable observations were thus secured from observers in all parts of the world. The results, some of which are given below, are now being discussed by Professor W. H. Pickering, and will be published later in the Annals. Similar observations are desired this year, and it is hoped that they may be made on November 15, and also on the two preceding and following evenings. The most important time for observation is from midnight until dawn, as comparatively few meteors are expected earlier. Observations are particularly needed at hours when they cannot be made at the observatories of Europe and America. In general, the time required for ten or more meteors to appear in the region covered by the accompanying map, should be recorded. This observation should be repeated every hour or half hour. If the meteors are too numerous to count all those appearing upon the map, the observer should confine his attention exclusively to some small region such as that included between the stars Ursae Majoris, 40 Lyncis, & and a Leonis. If the meteors occur but seldom, one every five minutes, for instance, the time and class of each meteor should be recorded. Also, note the time during which the sky was watched and no meteors seen, and the time during which that portion of the sky was obscured by clouds. Passing clouds or haze, during the time of observation, should also be recorded. The date should be the astronomical day, beginning at noon, that is, the date of early morning observations should be that of the preceding evening. Specify what time is used, as Greenwich, Standard, or Local Time. When a meteor bursts, make a second observation of its light and color, and when it leaves a trail, record the motion of the latter by charting the neighboring stars, and sketching its position among them at short intervals until it disappears, noting the time of each observation. If the path of a meteor is surely curved, record it carefully upon the map.

On November 14, 1898, thirty-four photographs were obtained of eleven different meteors. Their discussion has led to results of unexpected value. The greatest number of meteors photographed by one instrument was five. Only two meteors were photographed which passed outside of the region covered by the map, although the total region covered was three or four times as great. No meteors fainter than the second magnitude were photographed.

Photographs may be taken, first, by leaving the camera at rest,

when the images of the stars will trail over the plate and appear as lines, or secondly, attaching the camera to an equatorial telescope moved by clockwork, when a chart of the sky will be formed in which the stars will appear as points. A rapid-rectilinear lens is to be preferred in the first case, a wide-angle lens in the second. The full aperture should be used, and as large a plate as can be covered. The most rapid plates are best for this work; they should be changed once an hour, and the exact times of starting and stopping recorded. Care should be taken to stiffen the camera by braces, so that the focus will not be changed when the instrument is pointed to different portions of the sky, especially if the lens is heavy. If the first method is employed, the position of the camera should be changed after each plate, so as to include as much as possible of the region of the map on each photograph. If pointed a little southeast of Leonis, the radiant will reach the center of the field about the middle of the exposure. A watch of the region should also be kept, and the exact time of appearance and path of each meteor as bright as the Pole Star should be recorded. The plates should be numbered on the film side with a pencil, and should be sent to this Observatory with accompanying notes and other observations. After measurement here, they will be returned if desired. The value of the results will be much increased if similar photographs can be obtained by a second camera from ten to forty miles distant, and preferably north or south of the other. EDWARD C. PICKERING.

September 1899.

A LONG PHOTOGRAPHIC TELESCOPE.

The

LAST spring a plan was proposed at the Harvard College Observatory for the construction of a telescope of unusual length for photographing the stars and planets. Anonymous donors have now furnished the means by which this experiment may be tried. plan will, therefore, take definite shape, and it is expected that a telescope having an aperture of twelve inches and a length of a hundred feet or more will be ready for trial at Cambridge in a few weeks. EDWARD C. PICKERING.

NOTICE.

The scope of the ASTROPHYSICAL JOURNAL includes all investigations of radiant energy, whether conducted in the observatory or in the laboratory, The subjects to which special attention will be given are photographic and visual observations of the heavenly bodies (other than those pertaining to "astronomy of position "); spectroscopic, photometric, bolometric and radiometric work of all kinds; descriptions of instruments and apparatus used in such investigations; and theoretical papers bearing on any of these subjects, In the department of Minor Contributions and Notes subjects may be discussed which belong to other closely related fields of investigation.

Articles written in any language will be accepted for publication, but unless a wish to the contrary is expressed by the author, they will be translated into English. Tables of wave-lengths will be printed with the short wavelengths at the top, and maps of spectra with the red end on the right, unless the author requests that the reverse procedure be followed. If a request is sent with the manuscript one hundred reprint copies of each paper, bound in covers, will be furnished free of charge to the author. Additional copies may be obtained at cost price. No reprints can be sent unless a request for them is received before the JOURNAL goes to press.

The Editors do not hold themselves responsible for opinions expressed by contributors.

The ASTROPHYSICAL JOURNAL is published monthly except in July and September. The annual subscription price for the United States, Canada, and Mexico is $4.00; for other countries in the Postal Union it is 18 shillings. Correspondence relating to subscriptions and advertisements should be addressed to The University of Chicago, University Press Division, Chicago, Ill.

Wm. Wesley & Sons, 28 Essex St., Strand, London, are sole foreign agents, and to them all European subscriptions should be addressed.

All papers for publication and correspondence relating to contributions and exchanges should be addressed to George E. Hale, Yerkes Observatory, Williams Bay, Wisconsin, U. S. A.

[blocks in formation]

ON THE RELATIVE BRIGHTNESS OF THE PLANETS MARS AND JUPITER, FROM

WITH A NEW PHOTOMETER.'

By J. HARTMANN.

MEASUREMENTS

ATTEMPTS to employ the photographic action of light for the measurement of luminous intensity were made very soon after Daguerre's process became known. In the year 1844 Fizeau and Foucault compared in this way sunlight with terrestrial sources of light, proceeding on the principle that it would be permissible if, perhaps, only within narrow limits-to place the intensity of a source of light inversely proportional to the exposure in which the particular source produced a definite impression upon the photographic plate. Bunsen and Roscoe, employing chloride of silver paper, carried on further investigations, including the brightness of sunlight at different. times of the day and year, as well as the distribution of light on the solar disk, after they had proven that the above mentioned

[ocr errors]

1 Sitzungsberichte der kgl. Akademie der Wiss. zu Berlin. Session of the Physicalmathematical Section on July 20, 1899.

2 C. R., 18, 746, 860.

3 Phil. Trans., 1863, 139; Pogg. Ann., 117, 529.

« ÎnapoiContinuă »