8 
MESSES. DE LA EUE, STEWAET, AND LOEWY’S EESEAECHES 
“±-^-90= 4 3 20-5 6 =a' 
^-90=13 3 32-4 5 =j3' 
P'- a '= 90 11*9 
S= + 11-9 
A-H=+45 1-8 
- 2 =~ 5 - 9 5 
-(-^-90°) = -43 20-5 5 
Correction to readings = + 1 35*3 
The readings on the circle for the wires I., II., III., IV. are, as seen in the above 
example, accompanied by the corresponding scale-readings of the sun’s periphery at the 
wire-ends. They serve in the present instance chiefly as a control of the tangency of the 
microscope-wire, but will be of special use hereafter in an investigation on the sun’s 
diameter, which we have in view for a future occasion. 
9. The necessary corrections to the measurements being thus supplied, each group of 
spots as it appears on the photograph is then sketched, as represented in the accom- 
panying form, which fills the next two pages, and is an exact representation of that used 
by us. The first page serves for entering the measurements necessary for determining 
the centre of the sun-picture, its radius, and the necessary corrections, derived by the 
preceding methods ; while the second page contains the sketches of the groups, indi- 
cating by attached letters the different members of each group, the positions of which 
have been determined, and then gives for each of these members all necessary elements 
of calculation in five columns, viz. in 
Column 1, the distance of a spot from the periphery, in terms of the scale. 
Column 2, the distance of a spot from the centre, in terms of the scale ( r ). 
Column 3, the distance of a spot from the centre, expressed as a fraction of the sun’s 
Column 4, the circle-reading corresponding to the position of the spot. 
Column 5, the true angle of position, reckoned from north through east (east being 
left side of sun-picture) =P. 
Even the smallest spots have in all cases been measured ; and in larger spots, contain- 
ing several nuclei, the position of each nucleus has been determined. The point chosen 
for measurement was always the geometrical centre of the figure of the spot or nucleus, 
as far as careful estimation could ascertain it. Proper care has also been taken to 
