Oct. 26, 1871] 



ment. 
Instrument B.—An integrating spectroscope, mounted equato- 
rially, with clockwork or some equivalent arrangement, with 
' long collimator, and object-glass of such aperture that an angle 
of about 3° is taken in. ‘This, by means of a finder, should be 
directed to the sun’s centre. It should be furnished with a 
reference-spectrum, or ready means of record. 
Instrument C.—An analysing spectroscope of great dispersive 
power and automatic arrangement, attached to a clockwork-driven 
equatorial reflector or refractor, in the manner used for observa- 
tions on the Janssen-Lockyer method. 
| dnstrument D,—An analysing spectroscope of moderate or 
smail dispersive power, attached to an equatorial in the same 
manner. 
Instrument E —A hand integrating spectroscope. 
INSTRUCTIONS FOR USE OF INSTRUMENT A.—With this 
instrument it should be sought to determine, if possible :— 
1. The spectrum of corona visible before and after totality. 
_ 2, The spectrum of any bright rays visible before or after 
totality. 
_ 3. The spectrum of lowest layer of chromosphere just pre- 
_ ceding and following totality. 
_ 4. Whether there are any dark lines (attention to be directed 
_to D, E, 4, F only) in the spectrum of the corona during totality, 
"at any distance from the sun; and, if so, at what distance ? 
_ 5. The spectrum of any bright streamer seen during totality. 
_ 6. The existence and position of bright lines between D and 
1474 (Kirchhoff) during totality. 
7. Comparative heights of C, D’, F, and 1474 (Kirchhoff), and 
lines, if any, between D and 1474 during totality. 
8. The spectrum of the dark moon. 
The observations should be conducted as follows :— 
I. If reference-spectra are used, connect the bar carrying the 
_ spark-tube, by means of a piece of string, to the eye piece, so 
that the amount of light thrown by the small lens on to the slir, 
: 
and parallel to it, may be controlled. 
2. Carefully adjust the finder. 
3. Have a slit of such width that ona very faint cloud, with 
the whole aperture of the reflector, the principal lines of the 
solar spectrum are alone visible (the three lines of 4 should appear 
as two). 
4- Te the telescope-tube in order that the slit may lie along 
the line joining the points of contact at beginning and end of 
totality. 
5. The observer at the finder should bring the streamer on to 
the slit, without rotating the telescope-tube. 
6. If there are clouds near the sun, on no account move the 
telescope in right ascension, or meddle with the clock. 
INSTRUCTIONS FOR Use oF INSTRUMENTS B AND E.—With 
these instruments it is possible to examine the changes which 
take place in the quality of the total amount of light proceeding 
from the circumsolar regions during the whole time of greatest 
obscuration. The observations may be made, say, from half an 
hour before totality to half an hour after ; during totality, and if 
rapid changes are discovered before or after, the observations 
should be recorded every ten seconds or so, the times of com- 
mencement and end of totality being carefully noted, as it is im- 
portant to connect the changes observed with the amount of 
chromosphere visible. 
The observations should be conducted as follows :— 
1. Adjust the driving-clock carefully to solar motion. 
2. Adjust the slit so that most of the principal lines can be 
seen in the spectrum of a faint cloud. 
3. Point the instrument to sun’s centre three-quarters of an 
hour before totality, and connect the clock. ; 
4. As totality approaches, observe which dark lines fade out 
and then brighten, noting the relative intensity of such bright 
lines. 
5. Ad the instant of totality pay particular attention to the 
spectrum, in order to ascertain whether all lines are reversed, or 
only some. 
6. During totality note] every ten seconds all changes, 
especially of intensities, e.g. é 
1474 (Kirchhoff) 2s compared with. . . . . rE 
5 do Aare na 
Co 
oe Ke AD any lines between D & 1474 
Cvasicompared\with! sj). W-wiel Sf. su Ge FE 
” ” ” 
” ” ” L 
” ” ” 
NATURE 
1 
field, the height of this spectrum forming a standard of measure- 

517 
7. Note whether C entirely disappears. 
Repeat the foregoing observations in reverse order till all 
changes cease, 
INSTRUCTIONS FOR Use oF INSTRUMENTS C AND D.—It 
is important not only to compare observations made with instru- 
meats of large dispersion and those of smaller dispersive power, 
but to determine the obliterating effect of the atmospheric il- 
lumination, so as to render observations made during eclipses 
comparable with those made on the Janssen-Lockyer method. 
The observations with these instruments should be conducted 
as follows :— 
1. Before the eclipse commences sweep round the sun, and 
giving angles from the true north through the true east of the sun 
from 0° to 360°,* make a diagram of the chromosphere, its 
height being determined by the height of the C line ; especially 
note all prominences of both kinds (that is, the diffused and 
eruptive ones), and the amount of motion indicated by changes 
in wave-length. 
2. Find, near the point at which the sun will disappear, an 
average plane-topped region of the chromosphere where a little 
motion on either side does not brighten, or thicken, or lengthen 
the lines. 
3. Observe the spectrum of this, and of the gradually narrow- 
ing underlying region of photosphere, and note the effect of the 
diminution of the photospheric light ; such effect may probably 
be apparent before totality ; note increased number of lines, 
their relative heights, and whether there is a diffused band over 
6; note also the width of F. Nore also lines between D and 
1474, and which lines disappear as the moon covers the lowest 
layers of the chromosphére. The spectrum should be swept 
from C to G before totality, and from G to C immediately 
totality has commenced. 
4. Duiing totality determine how far from the dark moon any 
spectrum is visible, and what that spectrum is. The brightest 
part of the Ozéer Corona should be chosen for this observation, 
the telescope being directed to it by means of the finder. 
5. Observe the spectrum of a streamer, also, if there be time. 
6. Just before the end of totality watch the chromosphere 
above the point at which the sun will reappear. Observe the 
phenomena in reverse order. See III. 
PHOTOGRAPHIC OBSERVATIONS,—The instrument recom- 
mended to be employed during the eclipse of this year is a 
camera of about 4in. aperture and join. focal length, equa- 
torially mounted, and driven by clockwork. 
The pictures taken with such instruments should be exposed as 
follows, and negatives only should be taken :— 
Where the totality is about 2 minutes. 
Beginning. Middle. End. 
55 Te 1o° 15° 10° 7 ie 
Where the totality is about 4 minutes. 
Beginning. Middle. End. 
55S Ios 208 T5200) 205 1078.75" as 
To insure a given number of pictures, it is desirable to have the 
same number of baths and plaie-holders. 
If this system be carried out we shall be able— 
1. To use equal exposures for the examination of the Corona 
on either side the middle point of totalicy 77 each series. 
2. To compare pictures of equal exposure taken at the same 
time with reference to the middle of the phenomenon at a// 
stations, 
3. To determine the effect of exposure. 
TELESCOPIC AND NAKED-EYE OBSERVATIONS. +— Before 
| totality. 
1. Note how long the corona is visible before totality along 
the edge of the dark moon opposite the point at which the sun 
is about to disappear. 
2. Sketch any rays visib'e before totality ; give length, colour, 
and structure, as well as position. 
At commencement of totality. 
3. Sketch general outline and any rays (streamers) or rifts. 
4. Note if there be a blaze of light or glare where the sun 
has just disappeared. 
Middle of totality. 
* Diagrams should be prepared showing the N. and E. points of sun as 
| seen (1) withthe naked eye, (2) in an inverting telescope, and (3) ow te sizt 
plate of the spectroscope 
+ These observations should be made by observers ix fairs, and they 
should not compare notes. If teles.opes are thus used, 2 inches aperture 
and a power of 20 should be employed, 
