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Physics. — “Regular consequences oj irregular refraction in the 
sun .” By Prof. W. H. Julius. 
The images produced on our retina, or in the focal plane of a 
telescope, may be considered as geometrical projections of light-emit¬ 
ting objects. Our idea of the object, as derived from the shape of 
the image, is founded on the validity of that rule. If it fails to hold, 
if, for instance, the rays are curved in traversing a whirling mass of 
air, so that they no longer form homocentric beams, the distribution 
of the light in the focal plane will give us a false idea of the object. 
What we then observe is no “image”. 
We cannot possibly doubt that rays, in passing through extensive 
gaseous parts of celestial bodies, deviate from the straight line in an 
irregular way. If caught in a telescope, such rays do not form an 
image of the source of light. Yet our conclusions regarding distri¬ 
bution of matter, and other local conditions in the sun, have to be 
deduced from the phenomena visible in the focal plane. In inter¬ 
preting those phenomena we therefore are compelled to account for 
the probable course of the rays inside the celestial body considered. 
Most investigators of solar phenomena have so far never thought 
this necessary. Sun-spots, faculae, flocculi, prominences, are spoken 
of as if they were luminous “objects” from which our telescopes 
show us the geometrically projected “images”. This includes the 
supposition that the curving of the rays in the sun is too insigni¬ 
ficant to have any considerable influence on the phenomena. 
Astrophysicists, of course, cannot be ready to abandon their un¬ 
limited belief, that they are dealing with optical images of real objects, 
unless very strong evidence of the contrary be given. Indeed, at first 
sight such loss of confidence in familiar forms would seem to deprive 
us of almost every hold on the solar phenomena, and to doom all 
our notions to vagueness. But the step must be taken nevertheless, 
and we will try to show that the new way leads not to vagueness, 
but, on the contrary, to concise notions, by which the correlation 
of the principal solar phenomena can be clearly represented. 
On the degree of refraction probably existing 
in the solar atmosphere. 
We imagine the sun to be an incandescent mass, surrounded by 
a gaseous envelope, which we shall call the “solar atmosphere”. 
Whether the latter passes gradually or abruptly into the main body, 
does not matter for the present. The constituents of the atmosphere 
