578 
MESSES. LOCKYEE AND SEABEOKE ON 
then, the ring of chromosphere, as seen on the slit plate, be cut at North or 0° and 
straightened, we obtain a line with N. or 0° on the left hand, and extending to the 
right from N. 0° through E. 90°, S. 180°, West 270°, to N. 360°. 
The adjustments for recording the positions of various parts of the chromosphere as 
observed with either the radial or tangential slit having been made, the telescope is 
clamped in R.A., the clock set going, and the spectroscope focused for the C line. 
Should a prominence be observed, the telescope is moved in R.A. or Declination, 
until it appears in the middle of the field of the spectroscope, and the position-circle is 
then moved until the slit is either tangential or radial to the part of the limb where 
the prominence appears ; this is determined, in the case of the tangential slit, by the 
narrow strip of continuous spectrum which flashes in the moment the limb of the sun 
overlaps the slit exactly. 
In the drawings executed in London, which accompany this paper, the positions of 
the prominences have been determined as follows, viz. the smaller ones, those from 2° to 
3® wide, have had the central point of their base taken for the position, those wider than 
this have, in every case where possible, had the position-angle of each side determined, 
and very complicated groups have had, as far as possible, their principal components 
determined. 
The height has been obtained by causing the slit to travel up the prominence, and 
estimating how many slits high above the limb it was — a process which is easy, as there 
are nearly always in the prominence details of structure which can be used as points for 
measurement. 
The height of each prominence is set down in slits, and the width of the slit is 
measured at the end of the operation, and the true height in seconds calculated from 
the measurement. 
The London observations and drawings have almost entirely been made by Mr. R. 
J. Friswell, Mr. Lockyer’s assistant, to whom great credit is due for the zealous and 
intelligent manner in which he has taken up this branch of the research. 
EUGBY OBSEEYATIONS. 
The 8-g;-inch equatorial by Alvan Clark, to which is attached the ring-slit arrange- 
ment, producing a virtual eclipse of the sun, described by us before this Society in 
January 1873, has been used for these observations. The spectroscope attached is con- 
structed on the return principle, giving a dispersion of 8 prisms of (50°. The position 
of the prominences has been determined as follows : — Arranged radially round the 
disk, which cuts off the light from the body of the sun, are fine platinum wires at a 
distance of 10° from each other, and these being seen together with the ring of chro- 
mosphere serve to fix the position of the prominences, the shape and position-angle of 
which can be then easily drawn. There are four wires crossing the annulus 90° from 
each other that are rather thicker than the others, and these are made to coincide with 
the N., S., E., and W. points of the sun respectively by causing the upper or lower 
