January ii, 1900J 



NA TURE 



249 



THE ECLIPSE EXPEDITION AT VIZIADURG} 



II. 

 \XnTH regard to securing the best possible obser- 

 '' * vations along all lines, the perfect organisation 

 of time signals was of the first importance ; indeed, a 

 fundamental condition for success. The headquarter 

 staff, under Captain Batten, was stationed at the 

 eclipse clock, about which a word must be said. In 

 an eclipse, especially when there are as many ob- 

 servers as we had on this occasion, it is well that every 

 one shall know that he will get a good square look 

 ;it it some time or other. In early eclipse work this 

 was not recognised, and I never felt more annoyed in 

 my life than, when I was in India, in 1871, I found that 

 in consequence of my ignorance of eclipse organisation. 

 Captain Bailey, of the Royal Engineers, who travelled 

 400 miles to our camp to help us, did not see the eclipse 

 at all. He volunteered to give us the time, and took to 

 rehearsing the work daily. I said to him, " What you 

 liave to do is to put your chronometer on the table and 

 then sit down facing the sun, so that at any time you like 

 during the eclipse you can look off the face of the chro- 

 nometer and see the eclipse ; because now you have come 

 so far it won't do for you to go away without seeing 

 anything." He said, "Well, I have been practising for 

 the last two days, and I find it very difficult." I said, 

 "What are you going to do about it?" He replied, 

 " Well, I shall go on practising it till I do it." But to 

 my horror, just before the eclipse began, I saw him take 

 his chair to the other side of the table, deliberately place 

 his back to the sun and look at the chronometer, and he 

 never saw the eclipse at all. I was determined that that 

 should never happen again in any eclipse that I had any- 

 thing to do with, and since then I have always doubled 

 the timekeepers, and given one-half of the eclipse to one 

 timekeeper, and the other half to another. The "eclipse 

 clock" is of rather peculiar construction. It only pos- 

 sesses a seconds-hand controlled by a seconds-pendulum. 

 The face of the clock shows seconds, and a spiral on 

 which the times are marked, so that there can be abso- 

 lutely no mistake made as to the time. Not only can 

 the even seconds be given in that way, but if a signal at 

 any particular time is requisite for any particular opera- 

 tion in any of the observatories, the time signalman can 

 give that time as well, so that all the operations are kept 

 perfectly steady. The pendulum (and therefore the 

 clock) is started by cutting a thread at the word " go," 

 which means the beginning of the eclipse. Then one of 

 the timekeepers turns his back to the sun, stands in 

 front of the clock, and reads out the time-signals " 120 

 seconds left," and so on, which are marked along the 

 spiral, as the hand reaches them, while the other is looking 

 at the eclipse. The half-time signal ("60 seconds" on 

 this occasion) is sung out by both, and then they right- 

 about face, one man going off duty and the other taking 

 it up. In that way both see the eclipse. In order to give 

 an idea of the importance of keeping the time during an 

 eclipse, I will give our eclipse time table. 



.\t II o'clock the "Thermometer" party commenced 

 work. 



1 1. 1 2 a.m. — The " first contact" took place. 



12.16 p.m. — " Naturalists and Landscape" party com- 

 menced operations and were followed at 



12.30 p.m. by the "Slit Spectroscope and Prism" 

 parties. 



Ten minutes before "totality" Lieut, de Wet, with 

 an Admiralty chronometer "gave the word," on 

 which the " alert " was sounded on the bugle. 



At this signal— 



The " stops" were taken off telescopes. 

 Caps off siderostat and calostat. 



1 Continued from p. 23^. 



NO. 1576, VOL. 61 j 



Clocks wound. 



Timekeepers reported eclipse clock correct. 

 Observers at discs blindfolded. 

 Remainder of observers turned backs to sun. 

 Seven minutes before " totality " 3 " G's " were sounded 



on bugle as a signal to Prof. Pedlar with 6-inch. 

 25 seconds before "totality" — 90' from Lieut, de Wet. 



2 " G's " on bugle. 

 5 seconds before "totality "—45" from Lieut, de Wet. 



I " G " on bugle. 

 On the order " go " the first timekeeper, with his back 

 to the sun, called out " 127 seconds," and every 10 

 seconds till 17 seconds, followed by 10 seconds and 

 7 seconds, and then every consecutive second till 

 "over" was given. 



Why it was necessary to use the bugle will be seen at 

 once. That was the order given to the various parties,, 

 several of whom, especially the disc observers, were a long 

 distance from us. At the " alert " the stops were taken 

 off the telescopes ; a very wise precaution, for in some 

 eclipses even caps have not been taken off at all — there 

 were other things to think of I All the clocks were wound, 

 and the observers at the discs were blindfolded. Then all 

 the observers turned their backs to the sun in order that 

 they might not weary their eyes by trying to see a series 

 of phenomena of no interest to anybody. At 25 seconds 

 before totality we had two " G's " sounded on the bugle. 

 It had been determined that at that moment the un- 

 covered arc of the sun measured exactly 90°. It was 

 most important for the spectroscopic work that we should 

 get a signal 5 seconds before totality— that is to say, 5 

 real seconds before totality quite independent of any 

 errors in the Nautical Almanac. For the work of the 

 prismatic cameras it was important to get a signal as 

 nearly as possible five seconds before the beginning of 

 totality, and, in order to eliminate the possible error of 

 the chronometer, it was arranged to determine this by 

 direct observations. Captain Batten did a thing which 

 has certamly never been done in any eclipse expedition 

 before. We expected, of course, a very definite shadow, 

 and he was good enough to find a native dhow and 

 charter it, and anchor it in the roadstead at such a 

 distance that the shadow would strike it exactly 5 seconds 

 before it struck the camp. For another signal we calcu- 

 lated that 5 seconds before totality the portion of the 

 sun still visible w^ould subtend an angle of 45°. The 

 moment of totality was to be determined by means of 

 the 3|-inch. 



The Work Attempted. 



The Prismatic Cameras. 



In the two prismatic cameras about sixty photographs 

 were required, the exposures varying from one to fifty 

 seconds. These included two series of ten snap-shots at 

 the beginning of totality, and another ten at the end of 

 totality, and shots, of different periods, up to thirty-six 

 seconds in one case, taken during the totality itself. 

 That was done, of course, in the hope that one exposure 

 would be better than any of the others, so that we should 

 be sure of getting something at its best. Another reason 

 was that we hoped to get records of fainter phenomena 

 in the middle of totality than we were likely to do at the 

 beginning and end of it. It was necessary to throw the 

 sunlight into the camera by means of a mirror of a 

 siderostat. 



To carry out this programme of work, to secure the 

 results required, a minute subdivision of labour was 

 imperative. In the case of each of these two instruments 

 six volunteers were employed, and they were distributed 

 in the following manner : — 



One observer with the finder, his duty being to keep 

 the image in the centre of the field of view which corre- 



