350 Mr. William J. S. Lockyer [March 1, 



Total eclipses, as I may further remiud you, occur in families, 

 and each member of a family is separated in time by intervals of 

 a))out 18 years and 11^ days. The eclipse of April 2<S of last year 

 belongs to the family the last two deceased members of which lived 

 and died on April 16, 1898, and April 6, 1875, while the next one 

 yet unborn will exist for a brief interval on May D, 1929. 



It is not every total eclipse that lends itself to study, for some are 

 visible only from such unfavourable places as oceans, others from 

 the inaccessible arctic or antarctic regions, and others again from very 

 cloudy districts. 



The sum total of time spent in useful observation at all the 

 ecHpses which have been observed up to date is very short and 

 amounts probably to less than three hours, for an ecHpse cannot last 

 longer than eight minutes, and does not as a rule exceed three minutes. 

 The line of totality of last year's ecUpse extended across the Pacific 

 Ocean, commencing at New South Wales, Austraha, and terminating 

 in the ocean just to the west of Central America. The central por- 

 tion of the track passed near the Islands of Tof ua, Vavau, Tau, Nassau 

 and Danger Islands. Tof ua being an active volcano, and Tau, Nassau 

 and Danger Islands difficult of access, most of the expeditions located 

 themselves on Yavau, where there was a very safe anchorage for 

 ships and where stores were obtainable. All the parties settled close to 

 Neiafu, the chief village of Vavau, and there the duration of totality 

 was computed to be three minutes thirty-seven seconds, or 217 

 seconds. 



In the earlier days of eclipse expeditions those who took part in 

 them had to be content with eye observations alone. The discovery 

 and rapid advance made in the sensitive photographic plate and its 

 successful application in 1860 to eclipse work revolutionized eclipse 

 programmes altogether, so that an abundance of facts may now be 

 photographed in a brief interval of time, and these be examined at 

 leisure, at a less exciting moment. 



It is well to remember that many inquiries, which in the earlier 

 days formed part of eclipse programmes, need attention no longer. 

 Thus, for example, the corona was first thought to be the illuminated 

 lunar atmosphere until observations proved it to be asolarajipendage. 

 Further, during eclipses, the corona was supposed to be either quickly 

 rotating or pulsating visibly, but subsequent observations have shown 

 that during those times it is apparently as rigid and stationary as an 

 Indian order suspended in the sky. 



The prominences, those ruddy brilliant tree-like forms, which appear 

 during totahty at the edge of the moon's limb, were also considered 

 as belonging to oui' satellite, until observations in 1860 demonstrated 

 them as belonging to the sun. While we know that they are solar, 

 there is even now no necessity to waste time during eclipses, on either 

 the study of their forms, positions, or chemistry. The reasons for 

 this are that in 1868 a method was devised by which they can be 



