14 POPULAR SCIENCE MONTHLY. 



2.0 seconds only, generally one second being about right; the wet 

 plate will take the corona in eight seconds or less. The best time 

 of exposure should be tested on a bright star of about the second 

 magnitude, by trial before the eclipse. There is no rule about the 

 photographic focus, except to discover it by a series of exposures 

 at different distances near the supposed point. Eclipse work is a 

 practical matter, and many rough-and-ready methods must neces- 

 sarily be admitted. A good lens in a wooden light-tight tube, sup- 

 ported at each end, having the motion of the sun, the photographic 

 focal plane carefully determined, the time exposures very short, 

 and, finally, exceedingly slow development of the picture after the 

 eclipse — these form the prime requisites. Expensive telescopes, 

 clockwork on heavy iron piers, reflecting mirrors, and such like 

 apparatus are not needed. Ingenuity in practical details, with 

 great anxiety about the essential matter of the light itself, is what 

 is needed for a successful eclipse expedition. 



Those persons who have no telescope for viewing the sun, or 

 camera for photographing it, can yet see the corona to great ad- 

 vantage by means of a good opera glass, and indeed this is really 

 the most satisfactory way to thoroughly enjoy the spectacle. The 

 object may be sketched on paper at once or from memory, and this 

 picture may well be of value to astronomy. 



The tracks of the eight North American eclipses seen since 

 1800 are shown on Chart VI. It is noted that three have paths 

 very similarly located, and that five run in directions about parallel 

 to one another, but almost at right angles to the first group. This 

 comprises the eclipse of November 30, 1834, duration two min- 

 utes; August 7, 1869, two minutes and three quarters; July 29, 

 1878, two minutes and a half, which stretch from Alaska south- 

 eastward in a fan-shape to the South Atlantic coast. The second 

 group contains the tracks June 16, ISO 6, four minutes and a half; 

 July 17, 1S60, three minutes; January 11, 1880 thirty-two sec- 

 onds; January 1, 1889, two minutes and a quarter; and May 28, 

 1900, two minutes. These tracks all trend from southwest to 

 northeast, and cross the North American continent in different 

 latitudes, that of May 28, 1900, being the most southerly and of 

 rather short duration, lasting less than two minutes in the United 

 States. 



The path of the total eclipse of May 28, 1900, after leaving the 

 United States, crosses the North Atlantic Ocean to Coimbra, Por- 

 tugal, and continues over North Africa to its end at the Red Sea. 

 Stations which are not situated on the path of the totality will see 

 the sun partially eclipsed, in proportion to the distance of the 

 locality from the central line to the northern or the southern lim- 



