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and, if the eclipse is of short duration, which means a small shadow, the air

means o amoushadow the air thirty to forty miles away, where the sun is still shining, sends in a great deal of reflected and refracted light. Usually the hands of a watch can easily be seen; but in the case of a long totality (the greatest possible is 7 minutes 58 seconds), the darkness is more intense and artificial lights become necessary. There is one other phenomenon, occurring just before totality, which is still unexplained. Oni every white surface, just before the sun is completely covered, are seen rippling, shadow-like bands, which come and go. What causes them is still a mystery.

The observations which are of importance, and which can be made only during a total eclipse, are, according to Young :

(a) Times of four contacts, and direction of the line joining the cusps of the partially eclipsed sun. These determine with extreme accuracy the relative positions of sun and moon at the moment. (b) Search for intra-Mercurial planets.

socalled "shadow-bands”—which appear upon the surface of the earth for about a minute before and after totality.

(d) Photographic measurement of the intensity of the light at different stages of the eclipse.

(e) Telescopic observations of the details of the prominences and the corona.

(1) Spectroscopic observations, both visual and photographic, upon the “flash spectrum" and upon the spectra of the lower atmosphere of the sun, the prominences and the corona.

(g) Observations with the polariscope upon the polarization of the light of the corona.

(h) Drawings and photographic pictures of the corona and prominences. .

(i) Miscellaneous observations upon mneteorological changes during the progress of the eclipse-barometer, thermometer, wind, etc.and the effects upon the magnetic elements.

To these must be added the photographic work now done with all instruments; also the most recent project, that of photographing the corona and streamers with the three-color process, to obtain, as nearly as possible, a faithful rendering of the colors just as they appeared in the phenomenon itself.

Government Expeditions Inasmuch as the track of totality may be expected to strike any one place only about once in every 360 years, it is obvious, if we wish to study total eclipses of the sun, that we must go after them. Sending out eclipse expeditions is a recognized feature of astronomical work, and many large observatories are busily at work preparing for the eclipse which will be visible to certain parts of the earth on August 29 and 30, 1905. A glance at the accompanying map will

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A 65-FOOT CAMERA, WITH CELOSTAT, SHOWING LENS AND REFLECTOR. Erected on grounds of U. S. Naval Observatory.-Being tested by Mr. Pelus, Photographer of the Observatory.

show the limits of the eclipse as visible pedition is obvious. The large camera to the earth, and the path of totality. takes a large picture, and is intended to This path goes through the lower part make plates which shall record chiefly of Canada, across the Atlantic, through the phenomena nearest the sun. The Spain, the Mediterranean, the upper part small cameras, having a wider angle of of Africa, across the Red Sea, and across view, take smaller pictures, and are deArabia. Observations must be con- signed to picture the eclipse as a whole, ducted in the center of the line of totality, including the most lengthy coronal in order to get as much totality as pos- streamers. sible. To be most effective, they must The first party will locate on the cenbe conducted as nearly as possible at tral line of the eclipse, near Burgos, noon, which means the center of the Spain. It will have one large camera, track from end to end, in order to mini- with 5-inch lens, 40-foot focus, making mize the atmospheric effects which in- pictures on 14 by 17 inch plate; also one terfere more or less with all astronomical polar axis, with 81/2-inch lens, 12-foot foobservations. Consequently, in this par- cus, for ii by 14 inch plate, and one 6ticular eclipse, Spain and Northern Af- inch Dallmeyer lens of 36-inch focus, rica are indicated as the best regions in both for photographing the extensions which to locate parties. Here the United of the corona; besides spectroscopic States Observatory will locate three cameras. On the other end of the cæloparties equipped with the very best set stat running the big camera, will be a of instruments for photographic observa- plane-grating spectroscope, with lens of tions of an eclipse ever carried into the 5-inch aperture and 42-inch focus, for field for the purpose The Canadian plates 14 by 1 1/2 inches in size. This Government is also sending out an offi party is also equipped with one transit of cial expedition to view the eclipse from Venus ccelostat, with parabolic-grating some point in the Territory of Ungava. spectroscope.

For months the force at the Observa Party number two will locafe near tory at Washington has been busily en- Valencia, Spain. This party has the gaged in preparations for this, the big giant camera of this expedition, of 65gest event in the astronomical calendar foot focal length, equipped with a 712of work. The reader will understand inch triple achromatic lens specially made that astronomical instruments are not for this work by Brashear, after curves bought from a stock-house like a ready- computed by Prof. C. S. Hastings of made suit of clothes, but are specially Yale. It makes an image of the sun 7 designed for the work they have to do, inches in diameter. Besides this monster and not infrequently are largely made by instrument, shown in one of the illustrathose who design them. Of the instru tions, the party will have a polar axis, ments to be used by the three parties in with a camera in which is a 6-inch lens the present case, Mr. W. W. Dinwiddie, of 104-inch focal length, making picof the Naval Observatory staff, has de tures on an 8 by 10 plate, for use with a signed the three polar axes, the three color screen; also a 21-foot concave-gratportable dark rooms, the three portable ing spectroscope, used directly, on the houses which are the ends of the big sta- other end of the axis of the cælostat. tionary cameras, a ten-inch concave-grat- The third party goes to Sauk Ahauras. ing spectroscope, a new instrument called Morocco, and is equipped with a camera the “ chronospectrograph,” two cælo- of 40-foot focus, 5-inch lens; a polar stats, made by Gaertner, and in addition axis, on which is a camera with a 9has worked out the details of much of inch lens of 14-foot focus, for ii by 14 the remaining apparatus. The expedi- inch plates; and a 10-foot concave-grattions will be equipped, each with a sta- ing spectroscope, pointed directly at the tionary camera from forty to sixty-five sun. This party will also use Mr. Din· feet long, and each with a polar axis, on widdie's new chronospectrograph, an inwhich will be mounted a camera of from strument designed to give a continuous twelve to fifteen feet focal length, and photographic record of the spectrum of also spectroscopic apparatus. The neces- the eclipse, with the time of all the exsity of having two cameras for each ex- posures automatically charted; and in ad

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MR. W. W. DINWIDDIE OF THE L'. S. NAVAL OBSERVATORY STAFF, TESTING HIS NEW CELOSTAT

MIRROR ON A SMALL POLAR AXIS.

and each party has an outfit of dummy the greatest strides in discovery are glass plates, with ground edges to pre- made. These and other similar expedivent danger to the hands, so that the man tions may not add any new discovery apin the camera can learn to put a plate in preciable as such by the public (such as and get it out of the holder with the the photographic discovery of an intragreatest possible speed. The plates in Jercurial planet, for instance); but if these big cameras are handled naked, the the weather is fair and no hitches occur, plate end of the camera being a little the result should be a set of photographs house in which the photographer works. which, when studied, will add largely to These little houses, like the dark rooms, our all too small stock of information as were designed by Vr. Dinwiddie and go to what our sun is, and what causes so together and come apart without the use many of the inexplicable things that hapof a nail.

pen upon him and that he causes upon

the earth. For, while we know a lot What is to be Hoped for?

about him, when it is considered that he It is a little difficult to say exactly what is some ninety odd millions of miles is hoped for as a result of these expedi- away, still, what we know is infinitely littions, inasmuch as the average lay mind tle compared with what there is to know does not regard anything less than the and what we want to find out. Such exfinding of a new planet as an astronom- peditions as this, if successful, are better ical discovery worth noting. Astron- calculated to answer a few of our quesomers know, however, that it is from the tions than years of ordinary observation. vast amount of detail collected from dif- Let us wish the expeditions all possible ferent sources apparently unrelated, that success.

Marvels of Inventive Ingenuity and Mechanical Skill

By FRITZ MORRIS

Special Correspondent, The TECHNICAL World MAGAZINE

HERE is something irresistible, something fascinating in the charm of a timepiece—be it

watch, clock, or sundial—for all classes, and for all ages. The clocks of to-day, marvels though they are of mechanical or electrical skill, are no more ingenious than were those of two or three centuries ago.

Ancient Timepieces The development of mechanical devices to mark time makes an interesting chapter in human history. Probably the most ancient method of measuring the subdivisions of the day was by means of the sundial. This was followed by the water-clock, which was in use in Egypt, Judæa, Babylon, Chaldæa, and Phænicia. The first water-clock of which history tells us consisted of a basin of water exposed in some corner of a public place. At the extreme end of this vessel there

was a spout from which the liquid Aowed, drop by drop, into a receiver having graduations for indicating the hour of the day or night. The water-clock was in use until the seventeenth century. In Japan and China to this day is used a primitive measuring apparatus consisting of a wick, about two feet in length, which takes a certain period to consume. Knots are tied at intervals, which give an indication of the time. The sandglass is also of antiquity ; but to this day a sandglass is used in the British House of Commons to measure certain intervals.

Invention of the Watch About the year 1500, Peter Henlein, a young member of the Locksmith's Guild of Nuremberg, Bavaria, was engaging himself in improving the timepieces of that period, and he was vexed at the fact that the wheel clocks, the only ones then in existence, which depended for their

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