9382 REPORT—1885. 
disc for each whole degree is prepared, and is in fact an orthographic projection of 
a sphere turned through an angle equal to the latitude for which it is drawn. 
The proper disc for the day of observation is taken and set to the angle corre- 
sponding to the position angle of sun’s axis ; the disc is held at that distance from the 
eyepiece of the telescope, which allows the image of the sun to exactly coincide- 
with it. Thelatitude is then read off; and the longitude is found by taking the 
longitude of centre of disc given in the table, and subtracting or adding the 
difference as shown in the cardboard disc. 
The paper of which the above is an abstract had appended to it a set of card- 
board dises suitable for actual use, and tables required for the construction of 
these discs. 
WEDNESDAY, SEPTEMBER 16, 
The following Papers were read :— 
1. On the Nature of the Corona of the Sun.' 
By Witu1am Hveerns, D.O.L., LL.D., F.R.S. 
Mr. De La Rue in his address before Section A in 1872, said truly :—‘ The 
great problem of the solar origin of that portion of the corona which extends more 
than a million of miles beyond the body of the sun, has been by the photographic 
observations of Col. Tennant and Lord Lindsay in 1871 finally set at rest, after 
haying been the subject of a great amount of discussion for many years.’ (Report 
Brit. Assoc. 1872, p. 6.) 
Professor Hastings has recently revived the theory of Delisle that the corona 
is an optical appearance due to diffraction. He bases his view upon the behaviour 
of the bright line 1474, which he saw in his spectroscope change in length east and 
west of the sun, during the progress of the eclipse at Caroline Island in 1883. 
Captain Abney’s discussion of the photographs taken by the English observers 
shows that there was considerable diffusion during the eclipse, and that therefore 
the observation of Professor Hastings may have been due to a scattering by our air 
of the light from the brighter part of the corona, and therefore may not indicate: 
any change in the corona itself.” During the time that Professor Hastings observed 
the change in the length of the line 1474, photographs of the corona were taken by 
M. Janssen, and by Messrs. Lawrance and Woods. M. Janssen says: ‘ Les formes 
de la couronne ont été absolument fixes pendant toute la durée de la totalité,’* 
The photographs taken by Messrs. Lawrance and Woods (now in Captain Abney’s 
hands for discussion) show that the corona suffered no such alterations in form as: 
would be required by Professor Hastings’ theory during the passage of the moon. 
across the sun. 
The evidence seems to be conclusive that the corona which comes into view at 
a total eclipse corresponds to an objective reality of some kind existing about the 
sun. It is difficult on any other hypothesis to explain satisfactorily : 
1. The observed and photographed spectra which vary at different parts of the- 
corona. 
2. The visibility of the planets Venus and Mercury as dark bodies when near 
the sun. 
3. The filamentous, and especially the peculiar curved structures seen in photo-- 
graphs of the corona. 
1 The chief points of this discussion of the nature of the corona were suggested 
in a Discourse on the Solar Corona given at the Royal Institution, February 22, 1885. 
A more full discussion of these points will be found in the Bakerian Lecture, 1885,. 
in the Proc. Roy. Soc., vol. xxxix. p. 108. 
2 Report of Expedition to Caroline Island, 1883, Washington, p. 105. 
8 Annuaire pour Van 1884, p. 859. 
