4i8 



NATURE 



[Sk 



PTEMIiKK 3, 1896 



THE TOTAL ECLIPSE OF THE SUN} 

 II. 



Kill Island, Ai/t^iist 8. 



A LOVELY morning. The sun remained unclouded 

 till long' after eclipse time, giving thereby an addi- 

 tional proof of the advantage to us of the short nights. 

 There is no time either for any considerable reduction of 

 temperature or for the accumulation of any great amount 

 of moisture in the air ; hence unclouded sunrises, and the 

 sun strikes hot soon after rising. 



The beautiful harbour \n which the Volaffe is lying 

 looks its best in early morning, as the face of the nearly 

 vertical cliff, which swarms with bird life, lies nearly 

 west and south, facing eastwards. 



I am glad to say that the last adjustments have been 

 made, the last demonstrations given ; numerous re- 

 hearsals have landed us in the perfection of drill ; the 

 parties all know their stations, and ;l1I necessary forms 



Fig. s.— The yolage at anchor. 



have been written out. We are g'oing then to-day to 

 " stand easy," and take some rest in preparation for the 

 fateful to-morrow. 



I take advantage of the pause to continue my notes. 

 I confess I am keenly interested in our now tremendous 

 eclipse party. I will first of all, then, deal with its pro- 

 gress, and especially with the final arrangements made for 

 the larger instruments. 



The pfrsonini of each fi.\ed instrument is as follows. 

 Mr. Fowler has charge of the 6-inch prismatic camera, 

 and he receives the following assistance. 



As timekeeper Sub-Lieut. Beal offered his services, 

 and his duty is to give Mr. Fowler warning some 

 seconds before the commencement of totality, and to 

 record the times of exposure of the fifty plates intended 

 to be used. Roberts, an A.H., acts as exposer, taking 

 •off the cap from the i)rism at given signals. To 



' ConliiulL'il frotn p.i^Jc 400. 



NO. 1401, VOL. 54] 



economise the greatest amount of time, two marines 

 stand to Mr. Fowler's right and left, to hand and receive 

 the slides as they are inserted in and drawn out of the 

 camera. The exposures to be made arc generally very 

 short, in fact they are all snap-shots with the exception of 

 only two, one of them extending to half a minute. 



The plate-holders are ten in number ; each is capable 

 of holdmg five plates, which are exposed by slipping 

 them in turn into the focal image ; this operation is 

 controlled by a catch. The hut in which this instru- 

 ment is housed is one brought out from home ; the 

 framework is covered with waterproof canvas so arranged 

 that the roof can be removed at any time for observation. 

 A dark room for photographic work is also attached. 



The instrument under the charge of Dr. W. Lockyer 

 is also a prismatic camera, but of 9 inches aperture, 

 and rather differently mounted. The tube carrying the 

 camera, prism and lens is fixed horizontally, and the 

 light is thrown on to the prism by means of a siderostat. 

 The work intended to 

 be done is to obtain ten 

 photographs in all ; two 

 snap-shots, seven with 

 difierent times of ex- 

 posure, the greatest 

 amounting'- to thirty 

 seconds, and lastly, a 

 " dropping " plate. This 

 last-named is intended 

 to be exposed as near 

 as possible ten seconds 

 before the end of totality, 

 and carried through until 

 fifteen seconds after, the 

 plate being movedslowly 

 in the direction at right 

 angles to the length of 

 the spectrum. The ob- 

 ject of this motion is to 

 obtain an unbroken 

 record of the changes in 

 the spectrum during 

 this interval of time. 



.■\s timekeeper for this 

 instrument Midshipman 

 Bruce has been selected, 

 his duty being to keep 

 IJr. W. Lockyer in- 

 formed of the time a 

 few seconds previous to 

 totality, and also to note 

 the times and lengths 

 of the exposures made 

 during totality. One of 

 the ship's carpenters, 

 Sullivan, operates with 

 the cap in front of the prism, acting on instructions given 

 to him by the observer. Two bluejackets are also 

 employed in handing and replacing the dark slides as 

 they are required. 



The whole work of using the integrating spectroscope 

 is left to members of the ship's company. Lieut. Martin 

 has been selected as director, and he has as his assistants 

 Midshipman Woodbridge as "exposer," Midshipman 

 Brendon as timekeeper, and Midshipman Silvertop to 

 keep the sun's image on a small screen for the purpose 

 of correct orientation. 



The instrument is set up on a board inclined at the 

 angle representing the altitude of the sun at the time of 

 eclipse, and movable in azimuth by means of a milled- 

 hcad-driving screw turned by hand. By this means the 

 collimator can be directly pointed towards the sun, which 

 does away with the necessity of using a second siderostat, 

 and this is all the more important because we have not a 



