1912] Total Eclipse of the Sim, April 1911. 349 



WEEKLY EVENING MEETING, 



Friday, March 1, 1912. 



His Grace The Duke of Northumberland, K.G. P.C. D.C.L. 

 LL.D. F.R.S., President, in the Chair. 



William J. S. Lockyer, Esq., M.A. Ph.D. F.R.A.S. 



The Total Eclipse of the Sun, April 1011, as observed at Vavau, 

 T'onya Islands. 



It is my pleasant duty to-night to give you an account of the expedi- 

 tions which were sent out to oljserve the total eclipse of the sun of 

 April of last year visible in the South Pacific Ocean. 



Unfortunately, owing to very unfavourable weather, the eclipse 

 was observed in the presence of a large amount of cloud. I am 

 only able therefore to place before you a very few results in com- 

 parison with those I could have shown you had we been more kindly 

 treated. 



However, an opportunity is afforded me to attempt to give you 

 some ideas as to why expeditions are sent out to observe these pheno- 

 mena, and how a large expedition is organized when it is known that 

 the assistance of one of His Majesty's ships is available. Let me 

 remind you in the first instance that a total eclipse of the sun only 

 takes place when the moon passes directly between the earth and the 

 sun and completely covers the latter. At such times the brilliant 

 glare of day is discontinued for a brief interval of time, and in this 

 semi-darkness and weird illumination we see objects which surround 

 the disk of the sun that is usually only visible to us. 



Total solar eclipses are more common than is generally supposed, 

 for they occur almost every year ; but as the apparent diameter of 

 the moon is never much greater than that of the sun, the area on the 

 earth's surface — on which, at any one instant, the eclipse appears 

 total — is very seldom on the average greater than lOU miles in 

 diameter. 



The rapid motion of the moon round the earth, part of which is 

 counterbalanced by the rotation of the latter, causes the region on 

 the earth — from which the eclipse can be seen — to move along faster 

 than lOOU miles per hour, producing a shadow track on the earth 

 seldom wider than 100 miles, but sometimes more than 5000 miles 

 long. On this track the eclipse is tottd some time between sunrise 

 and sunset. On either side of it the sun is seen partially hidden and 

 appears crescent-shaped, but such partial phases are of little or no 

 value to those who study the physics of the sun, and only of passing 

 interest to even the " man in the street " as a spectacle. 



