298 



DISCOVERY 



North Pole in June 1295. On August 27, 1367, it 

 made its first appearance in the north of Europe ; in 

 1439 it was visible all over Europe ; in 1601, its 

 eighteenth appearance, it was central and annular in 

 England. It appeared a^^ain in June 1908, and will 

 return in July 1926. At its thirty-ninth appearance, 

 the shadow track will have passed the Equator. The 

 family continues to travel south, and finally it will 

 disappear in 2665. 



There are twelve families of total eclipse tracks in 

 existence at any one time. Six of them are moving 

 north, and six moving south. When one family goes 

 out at one Pole another comes in at the other, and 

 thus their number is kept constant. 



The next new family will come in at the South Pole 

 on May 29, 1938. The series of particular import- 

 ance to Britishers, however, is that which contains 



Fic. (.—PATH OF TOTAL ECLIPSE OF 1027. JCXE 29. 



the eclipse of 1927, for in that year the track \\ill 

 cross the north of England. The eclipse will take 

 place on June 29, and will be total along a band 

 including Conway, Liverpool, Southport, Lancaster, 

 Ripon, and Durham, the central line running from 

 St. David's Head to a point between Whitby and 

 Hartlepool. It will be the first one visible as such in 

 the British Isles since May 22, 1724, an interval of 

 more than two hundred years. 



The path just described will be traced out in the 

 morning ; so will be the beginning of the track, 

 which will pass on to Scandinavia and Northern Asia. 

 At its fourth subsequent return, that of 1981, the 

 beginning will be displaced sufficiently to miss the 

 British Isles, but at the following return, on August 11, 

 1999, the middle section of the track will just graze 

 the extreme west of Cornwall. 



Since there are only twelve families of total eclipses, 

 and each recurs but once in eighteen years, it follows 

 that a total eclipse cannot take place annually. The 

 way in which eclipses do actually occur will be seen 

 from the following list, which covers the eighteen 

 years, and so includes one member of each family. 

 The maximum duration of each is given. 



The approximate date of the next member of any 

 family may be obtained by adding eighteen years. 



The series which includes 1937 is remarkable for 

 the long duration of total eclipse. Those of 1937 and 

 1955 will fall not more than 20 sees, short of the absolute 

 maximum of 7 mins. 30 sees. But the 1934 series 

 will increase to even greater duration, reaching in 

 2150, June 25, a length of about 7 mins. 16 sees., and 

 in 2168, July 5, a length of 7 mins. 28 sees., the longest 

 hitherto known in historical times. The former will 

 pass over the Pacific Ocean, the second over the 

 southern part of India near Madras. 



It will be noticed that both these eclipses occur 

 near midsummer. As a general rule, a summer 

 eclipse is likely to be of longer duration than one 

 which takes place in the winter, for in the summer 

 the earth is at its maximum distance from the sun, so 

 that the latter appears to be of minimum size, and 

 can therefore be concealed by the moon for the 

 greater time. 



The Saros is, of course, the most important period 

 of eclipse recurrence, and is the governing factor of 

 the " families." There is, however, another important 

 period. This contains 10,571-95 days, about 20-3 

 days less than twenty-nine years. But in this period 

 the eclipse may vary from total to annular. Thus the 

 annular eclipse of February 14, 1915, will be followed 

 by a total eclipse on January 25, 1944 ; that total on 

 April 16, 1893, was followed by the recent annular 

 on March 27, 1922 ; but the total eclipse of May 28, 

 1900, will be succeeded by a total eclipse again ^on 

 May 9, 1929. 



It might sometimes happen that even the same 



