OcTor.EK, 1901.] 



KNOWLEDGE 



this the corona in general was sought to bo securc<l, 

 whilst with a Rapid Rectilinear lens by Dallmeyer, 

 giving an image of 0.3-inches, the outermost ext^nisions 

 wore aimed at. These three instruments, together with 

 a prismatic camera, lent to the expedition by Mr. 

 Evei-slied. were not pointed up (o the sun, but were 

 mounted iu a horizont.al position, the light from the 

 eclipse being rellecled into tliem bv means of a ccrlostat. 

 The Mauritius photoheliograph and the Rapid Rccti- 

 liuear lens were mounted the one under tho other in 



227 



a rainbow due (o tho corona 



Fig. 4.— Our Military Helper?. 



connection with one cojlostat. which had a mirror of 

 16 inches diameter, the prismatic camera and the 

 Greenwich coronagraph in connection with a second, 

 furnished with a 12-inch mirror. 



Mrs. Maunders progiamme and equipment were en- 

 tirely independent of the foregoing. Her first pui-pose 

 was to repeat with the same instruments the photogi-aphs 

 obtained in India in 1898, and in Algiers in 1900, and 

 she consequently brought the stigmatic lenses and the 

 " Xiblett " eclipse camera belonging to the British 

 Astronomical Association which had been used on those 

 occasions. The great kindness of Mr. Xewbegin, f.r.a.s.. 

 furnished her also with the beautiful photo-visual tele- 

 scope which Mr. Thwaites used in 1898 in India, and as 

 its aperture was little over 4-inches, and the diameter of 

 its image 2/3 of an inch, the photographs obtained with 

 it supplement most usefully and instructively the three- 

 fold series of the official programme. The equatorial 

 and camera bequeathed by the late Mr. Sidney Waters 

 to the Royal Astronomical Society, and used in tho last 

 two eclipses, were also both part of Mrs. Maunder's 

 equipment. 



The weather on the morning of tho eclipse was the 

 most favourable of any morning since our an-ival at 

 Mauritius. A heavy bank of clouds did, indeed, hide 

 the first contact from us, but this had passed and the 

 light scud that followed it haxl also entirely cleared 

 away before the eclip.se became total. The sky wa*; 

 completely clear therefore during the fateful minutes, 

 but not with anj-thing like that purity and transparency 

 with which we had been favoured on the two last 

 occasions. Indeed, at Curepipe, some fifteen miles away, 

 the whole spectacle was completely lost through cloud, 

 and at Quatre Bomes, twelve or thirteen miles distant, 

 a fine drizzle — locally known as " Moka dust "--fell 

 _^ during totality from a sky apparently clear, and gave to 

 the fortunate watchers located there the unique spectacle 



of an " eclipse rainbow, 

 and prominences. 



This want of perfect clarity in tho atmosphere is no 

 doubt tiio reason for the following unmistakable result. 

 It will be remembered that after our success with the lit- 

 tle stigmatic lens in India in 1898, we set ourselves to ask 

 tho question as to whether the exposure of 20 seconds 

 which we had then given was the longest which could bo 

 given with advantage. Tho answer in 1900 was that an 

 exposure of IS seconds had no advantitge as to length of 

 coronal streamers shown over an exposure one-sixteenth 

 that duration. Tho answer to the same question as 

 asked iu Maimtius was more decisive still in tho samo 

 direction. Tho longest streamers that we obtained wei'e 

 due to the Ncwbcgin telescope, and correspond to about 

 a second's exposure with the stigmatic lens. This result 

 is not the ono we should have liked to have got, but a 

 result is always worth getting whether it accord with 

 one's predilections or not. The result we obtained is 

 not the solution of the problem as to whether tho actual 

 length of the coronal streamers varies from eclipso to 

 eclipse, but only that, for this eclipse, our longest ex- 

 posures exceeded that of greatest efficiency under tho 

 actual atmospheric conditions. 



As a series the finest set of photographs wo obtained 

 were tho fourteen taken by Jlr. A. Walter during 

 totality with the Ncwbcgin telescope, two of which are 

 reproduced in the accompanying plate. It is sufficiently 

 well known that tho corona is by far the most difficult 

 object for photographic reproduction, and any photo- 

 mechanical process such as that employed for the plates 

 in Knowledge ncccs-sarily fails to do more than exhibit 

 the general distribution of light in tho corona; its 

 delicate details completely elude representation. Yet 

 full as the original photographs are of beautiful detail — • 

 and as pictures of the lower corona, I do not think that 

 finer photograplis than these and some of those taken 

 with the Greenwich coronagraph have ever been ob- 

 tained — the corona, as a whole, must be pronounced as 



i'ui. 5. — Hiotof^rapli of tlie riu-iial Phase, taken in Port, 

 J.oiiis Harbour l)y the t'hief Otii.-cr of the s.s. " Ugiuu." 



distinctly simpler than that of last year; it is of a yet 

 more pronounced minimum type. It is confined even 

 more strictly to the four same regions; the east and 



