Manchester Memoirs, Vol. I. ( 1 906), No. 7. 9 



of leap years) days. The one-third of a day is important, 

 because it moves the eclipse track on the earth's surface 

 just one-third round the earth at each recurrence ; so that 

 for the third recurrence (that is, after 54 years, i month, 

 and a few days) the track comes back nearly to the same 

 position. Nearly, but not quite, since all these figures are 

 approximate only, and not exact. The track is moved a 

 little north (or a little south) every 54 years, and ultimately 

 disappears from the earth at the north (or south) pole. 

 But to replace any family which dies in this way, another 

 one is born, so that the total number recurring in the 18 

 years is always about twelve. A new family is to be born 

 at the North Pole in 1909, which is of special interest to us, 

 because at its second recurrence (on June 29, 1927) the 

 track crosses the North of England ; and for the first 

 time since 1724 we shall be able to see a total eclipse 

 without leaving England. The track is a little unkind to 

 Manchester, which is left just outside ; so that it will be 

 necessary for this Society to make an eclipse expedition 

 to Liverpool. The duration of totality is also very short — 

 only 25 seconds — but the occasion can nevertheless be 

 recommended to everyone as one of remarkable interest, 

 and there is plenty of time for leisurely preparations. 



The observations to be made at a total eclipse vary 

 greatly in character. We may direct attention to the 

 parts of the corona lying near the sun, or to the fainter 

 parts at a distance : we may study its form, and its 

 possible changes of form ; or its sj^ectrum, and variations 

 in spectrum ; or the polarisation of the light ; or we may 

 leave the corona altogether and look for planets close to 

 the sun, for seeing which a total eclipse affords a unique 

 opportunity just as for the corona. One modern feature 

 of all such observations may be emphasized — they are 

 nearly always photographic. It is easier and safer to 



