138 
POPULAR SCIENCE REVIEW. 
obtained during the recent eclipse respecting the prominences 
and sierra; for the study of these objects proceeds under far 
more favourable conditions when the sun is not eclipsed. Yet 
the method of observation employed by Professor Respighi 
enabled that careful observer to enunciate some interesting 
facts bearing on the condition of the coloured appendages. His 
method was specially intended to reveal the true extent of the 
self-luminous gaseous atmosphere or atmospheres surrounding 
the sun. He thus describes it : ‘It appeared to me that the 
form and dimensions of the corona might be very conveniently 
studied by means of a large prism fixed in front of the object- 
glass of the telescope, whereby the several chromatic images of 
the corona would be distinctly formed in the focal plane. If 
the prism has but little dispersive power, and the eye-piece does 
not magnify too much, all the chromatic images of the corona 
may in this manner be observed simultaneously in the same 
field, and their form and dimensions directly investigated.” 
The essential point in which this method (originally employed 
by Fraunhofer) differs from the ordinary method of studying 
celestial objects with the telespectroscope, consists in this, that 
in the ordinary method we examine prismatically the image or 
part of the image formed by the telescope, whereas in Respighi’s 
method the prismatic images of the object are examined through 
the telescope. The prism used by Respighi was made by Merz 
of Monaco in 1868. “ My conviction,” says Respighi, “ of the 
great advantages which would be afforded by this instrument 
in the observation of the eclipse, induced me to carry it to 
India for that purpose,” and he adds that he was glad to hear 
that Mr. Lockyer “ had in like manner resolved to observe the 
corona by means of a spectroscope without a slit, being per- 
suaded that this would be the most convenient method of 
solving the questions related to the corona itself.* Mr. Lockyer 
used the ordinary form of telespectroscope, only that a simple 
train of prisms without any slit was employed, according to a 
suggestion made early in 1871 by Professor Young of America. 
It will be obvious that so long as the visible solar crescent 
was considerable, the solar spectrum seen by Respighi would be 
* By some mistake it was stated in an interesting and ably written 
account of the eclipse in the “ Daily News/’ that Professor Respighi adopted 
his method as the result of a consultation with Mr. Lockyer. It will be seen 
from Professor Respighi’s account that this was not the case. It may be 
added that in the same account the open-slit method of studying the 
prominences is called by mistake the Janssen-Lockyer method. Huggins 
and Zollner independently devised the method, which was first successfully 
applied by Dr. Huggins. (See Schellen’s u Spectrum Analysis,” English 
edition, p. 425.) 
