December 5- ^9°?] 



NA TURE 



105 



is not certain whether it will be " total " or " annu- 

 lar." This uncertainty is due to the fact that the 

 apparent diameters of the sun and moon on that occa- 

 sion will be so very nearly equal that it will depend 

 on the value of the moon's diameter employed in the 

 computations whether the sun will be totally eclipsed 

 or not. Should it prove, however, to be total, the time 

 of duration will probably be very short. Such an 

 eclipse would most probably be a very valuable one 

 from the point of view of the spectroscopic study of 

 the chromosphere. 



It will thus be seen that we shall most probably 

 have to wait until October, 1912, for a favourable 

 eclipse following that of 1908, so it is hoped that the 

 approaching event in the Pacific will be" satisfactorily 

 observed. 



The accompanying map of the world (Fig. 2) shows 

 the tracks of all 'the eclipses to which reference above 

 has been made, with the exception of that of April, 

 1912. This chart is taken from Mrs. Todd's ex- 

 cellent little book, entitled " Total Eclipses of 

 the Sun " {1S94), but all those tracks which were 



Fig. 2.— Chart showing the tracks of all the total solar eclipses from 1895 t 

 eclipse is included also, but the uncertain total eclipse of April, iqr2, 

 Spain, is excluded. 



not required have been deleted, and the year of 

 occurrence of each eclipse has been printed in larger 

 tvpe. 



It is interesting further to point out that the 

 eclipse of 1905 occurred at the time of greatest solar 

 activitv as indicated by the sun-spots, while that of 

 1912 will take place about the epoch of minimum 

 sun-spots. 



The eclipse of 1908, occurring in an intermediate 

 vear, will therefore be a useful connecting link between 

 the two, and renders it important even from this point 

 of view alone. 



The only official expedition which, so far _ as is 

 known, has made preparations to view this eclipse is 

 the one from the Lick Observatory in America, under 

 the direction of Prof. W. W. Campbell. Flint Island 

 will be the observing station, and Mr. William H. 

 Crocker, of San Francisco, who has defrayed the 

 expenses of five previous expeditions, has again offered 

 to finance this one. The Navy Department of the 

 United States has come forward and provided a war 

 vessel to transport the expedition from Tahiti to Flint 



NO. 1988, VOL. ']']'[ 



Island and back. The ship put on this special duty 

 is the A)inapolis, and she will be under the personal 

 command of His E.xcellency Governor Moore, U.S.N. , 

 of the Island of Tuituila, Samoa. 



No doubt the officers and men of the Annapolis will 

 prove most valuable assistants to Prof. Campbell, as 

 they were found useful in the eclipse of 1905. On 

 that occasion, it may be remembered, the United 

 States Navy Department sent a " special eclipse 

 squadron " of three vessels to Europe, under the com- 

 mand of Rear-Admiral C. M. Chester, U.S.N., the 

 result of which was a complete series of observations 

 only the preliminary results of which have as j'et 

 been published. 



To describe briefly the scientific staff and instru- 

 ments which will be conveyed by the Annapolis, 

 reference has been made t.j the contents of an article 

 which recently appeared in the Journal of the Royal 

 .Astronomical Society of Canada (vol. i., No. 4, p. 

 254) from the pen of Mr. C. A. Chant. 

 ' It is there stated that the party will probably con- 

 sist of Prof. Campbell, with Messrs. .'\itken, Perrine, 

 and Albrecht, of the Lick Observ- 

 atory ; Prof. Lewis, of the Uni- 

 versity of California ; Prof, .'\bbot 

 and his assistant, and possibly 

 one or two other assistants^ 

 They will all sail from San Fran-- 

 cisco on November 22, arriving 

 at Tahiti on December 4. The- 

 party will then join the Anna- 

 pnlis and sail for Flint Island. 



With regard to the instru- 

 mental equipment, corona pic- 

 tures on a large and small scale 

 will be secured by a 40-feet focaf 

 length coronagraph pointed 

 straight at the sun, and by a 

 5-inch objective of 70 inches focal 

 length respectively. For the pur- 

 pose of searching for intra- 

 Mercurial planets, two groups of 

 four cameras each will te pointed 

 towards the east and west equa- 

 torial regions of the sun's sur- 

 roundings. Objective-p r i s m 

 spectrographs, or prismatic 

 cameras as they are often called, 

 will be employed for obtaining 

 photographs of the spectrum of 

 the chromosphere. In one of 

 these " running " plates will be 

 used to record the sequences of changes in the spec- 

 trum of the sun's limb about the times of second and 

 third contact. 



This method was, so far as I am aware, first 

 employed at Sir Norman Lockyer's suggestion in the 

 prismatic camera in my charge at the eclipse of 1896 

 in Lapland. Unfortunately, clouds prevented any 

 photographs at all being secured. Prof. Campbell 

 successfullv applied the method to the eclipses of 

 1898, 1900, and 1905, and therefore proposes to con- 

 tinue the series. 



Other spectrographs included in the programme 

 are one of low dispersion for recording the general 

 structure of the corona, another for the determina- 

 tion of the wave-length of the green coronal line, and 

 a third for studying' the form of the gaseous envelope 

 responsible for the green line. For the ultra-violet 

 spectrum of the corona. Prof. Lewis is taking out 

 a large quartz spectrograph. Polariscopic photo, 

 graphs will be undertaken, and a study of the bright- 

 ness of the corona as a whole will be attempted. 

 From the above brief sketch it will be gathered 



.vhich might be seen fron: 



