ON PHOTOGRAPHING THE SOLAR CORONA. 349 
desirable to introduce into the apparatus for the purpose of preventing 
any light but that from the sun and the sky immediately around it from 
reaching the plate, the extent of field in which the full aperture was in 
use was small. For this reason it was found of advantage to place the 
sun’s image near the margin of the diaphragm limiting the field, and 
afterwards to combine the photographs, taken in four different positions. 
The moving shutter being placed very near the sensitive surface, and 
practically in the focal plane, could not give rise to effects of diffraction 
upon the plate. Besides, the opening in the shutter was never less than 
half an inch in width, and often as much as an inch or even more, accord- 
ing to the sensitiveness of the plates used. 
The most serious difficulty with which I have had to contend has been 
the absence of clear skies. On many days of bright sunshine the wind 
has been in a northerly direction bringing here the smoke of London, 
which produces a whity condition of sky, through which it was obviously 
hopeless to expect the coronal light to show itself upon the plates. 
The few occasions of a better condition of sky were for the most part 
of short duration and did not allow time for a large number of photographs 
to be taken. 
During the summer about fifty photographs have been obtained, 
which show photographic action about the sun of a more or less coronal 
character. 
I placed these plates in the hands of Mr. Wesley, who has had very 
great experience in making drawings from the photographs taken during 
several solar eclipses, with the request that he would make a drawing for 
each day on which sufficient photographs had been taken, combining the 
results of the different photographs in one drawing. This was desirable, 
as whenever a sufficient duration of sunshine permitted, photographs were 
taken on silver chloride films, as well as on silver bromide plates; some 
photographs were taken with the sun screened by the brass disk, others 
without it; also photographs were taken with the sun in different positions 
of the field. Asa rule, Mr. Wesley has introduced into his drawings 
those coronal features only which are common to all the plates taken on 
that day. 
The apparatus is attached to the refractor of the equatorial in such a 
way that the direction of the length of the plate is in that of a parallel of 
declination ; a line, therefore, across the plate is in a direction north and 
south, and from the date of the photograph the angle of position of the 
sun’s axis can be found. On Mr. Wesley’s drawings the orientation is 
marked, as well as the position of the sun’s axis. Four drawings accom- 
pany this paper. In most of the negatives more structure than is shown 
in the drawings is suspected when the plates are carefully examined. 
I regretted greatly that on May 6, the day of the solar eclipse, the sky 
here was very unfavourable. Up to the time of writing this paper I have 
not seen the photographs taken during the eclipse. Mr. Wesley wishes 
me to state that he has not seen the photographs or any drawings of the 
eclipse, and that therefore he has been wholly without bias in making his 
drawings from my plates. If these drawings are compared with the 
photographs taken during the eclipse, it should be borne in mind that 
the absence of sky illumination during the eclipse would allow a larger 
part of the fainter and more distant regions of corona to be photographed, 
and that any peculiar conformations or detailed structure of these outer 
portions could not be expected to be seen on my plates. The comparison 
