a a = 
of observing contacts at the Sun’s limb. 373 
tween important lines, covering the whole length of the spec- 
trum from A to G. Above G, Angstrém’s map was made the 
asis. 
In order to observe the first contact I had provided myself 
with a solar eye-piece which could be used upon the comet- 
seeker without disturbing the spectroscope ; but about half an 
hour before the totality the idea presented itself that a more 
accurate result could be obtained by means of the spectroscope 
than in any other way—ihus: i 
Suppose that by means of the tangent screws and the posi- 
tion lines on the screen-disc, that part of the sun’s limb at 
which the contact is to take place is brought across the center 
of the slit and kept there by the slow motion. pred 
Under ordinary circumstances, if the eye-telescope is di- 
rected upon the C line, the appearance will be what I have 
roughly represented in fig. 2, The spectrum will be divided 
into two portions by a longitudinal line of demarcation. One 
half of it, formed by the disc of the sun itself, will be intensely 
