[ ^ll ] 
XL Preliminary Report on the Results obtained with the Prismatic Cameras 
dunng the Total Eclipse of the Sun, April IG, 1893. 
By J. Norman Lockyer, C.B., F. R.S. 
Received February 22,—Read May 10, 1894. 
[Plates 9-11.] 
During the total eclipse of 1871 observations were made by Respighi and myself 
with spectroscopes deprived of collimators, and a series of rings was seen corre¬ 
sponding to the different rays emitted by the corona and prominences. The phenomena 
were so distinct that I made arrangements for a repetition of the observations during 
the eclipse of 1875, and an instrument, which received the name of “prismatic 
camera,” was arranged to photograph the rings. ^ The chief advantage of the instru¬ 
ment is that it combines the functions of a telescope with those of a spectroscope, and 
gives spectroscopic views of the solar surroundings in each radiation. The object- 
glass employed on this occasion had an aperture of 3f inches and a focal length of 
5 feet, while the prism had a refracting angle of 8 degrees. Two photographs were 
obtained, showing several protuberances in addition to continuous spectrum from the 
corona. 
I again employed this method of observation during the eclipse of 1878, but failed 
to see the rings, the corona apparently giving only a continuous spectrum. 
The method has also been attempted during succeeding eclipses, but on so small a 
scale that the results obtained have not come up to the expectations i-aised by my 
observations of 1871. Subsequent solar investigations, however, confirmed my 
opinion that this was the best way of studying the lower parts of the sun’s atmosphere, 
providing an efficient instrument were employed. 
As the Solar Physics Committee is now in possession of a prismatic camera of a 
much larger size than those used during the eclipses in question, I determined to 
employ it during the eclipse of 1893, the work on photogi aphic stellar spectra at 
Kensington having given abundant proof of its excellence. The object-glass of this 
instrument has an aperture of 6 inches, and was corrected for the photographic rays 
by the Brothers Henry. The correction is such that it is unnecessary to incline the 
back of the camera, and hence some of the objections which have been made to the 
MDCCCXCIV.—A. 
* ‘Phil. Trans.,’ 1878, vol. 169, p. 139. 
15.11.94 
