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rather smaller than the Sun . A ring of light thereforeremains visible, even to observers who are exactly in thedirection of the straight line joining the centres of the Earth ,the Moon , and the Sun ; and the eclipse is termed annular.
At no time can the maximum breadth of the Moon ’sshadow, where it falls upon the Earth , exceed 173 miles,nor will it often approach very near to this value. Whateverthe width of the shadow may be. it rapidly sweeps across azone of the Earth of corresponding breadth, with a relativespeed, which (when the rotation of the Earth is taken intoconsideration) may only amount to about 20 miles perminute. While it is passing over any place a total eclipseof the Sun, the most impressive of all celestial phenomena,continues. The above figures (by dividing 173 by 20) wouldallow the greatest duration to be fully 8^ minutes, but moreaccurate calculations give 7 minntes 58 seconds as the extremelimit, under the most favourable conjunction of circumstances.As an instance of one of long duration we may mention thevery notable eclipse of August 17th, 1868, in which the totalitylasted in the Gulf of Siam for nearly 7 minutes.
Upon either side of the zone of totality a wider, zone exists?in which a partial eclipse is seen, of greater or less magnitude,according to the distance of the observer from the central zone.But the phenomena thus produced are of comparatively littleinterest or importance.
Solar eclipses occur upon the whole with greater frequencythan those of the Moon . But the width of the zone of theEarth , in which the totality of any one can be seen, being,as we have explained, very narrow, a total solar eclipse isexceedingly rare in any given locality. The last visible inEngland was in 1724, in London in 1715. With the exceptionof a possible totality of a very few seconds, which may occurover a line drawn from the Isle of Anglesey across Northum-berland on June 29th, 1927, and which, in any case, must beso slight as hardly to deserve the name, none will, we believe,be seen in these islands until August 11th, 1999, when a shorttotality will occur in the south-western counties. None willprobably be visible in London for more than 500 years from