171 
The Angles are reckoned towards the right hand round 
the circumference of the Moon’s image as seen in an invert- 
ing telescope. 
Mr. Brothers, F.R.A.S., stated that when a solution of 
nitrate of silver, which, from long use, has become con- 
taminated with organic matter from collodion plates, is 
neutralized, or made alkaline with carbonate of soda, exposed 
to strong day-light in an evaporating dish, and heat applied, 
a scum is quickly formed on its surface. This scum, when 
broken by a puff of air exhibits, in a remarkable manner, 
all the appearances of solar spots as seen in good telescopes. 
So long as the current of air is continued the scum remains 
open at the spot, but immediately closes partially on the 
cessation of the cause, and streams of the film stretch across 
the opening, illustrating the bridges over the sun spots. At 
the same time a secondary scum commences to form at the 
edges of the opening, and may be called the penumbra, and 
in time closes the opening. The centre is occupied by the 
umbra formed by the carbonate of silver (white when first 
formed) which has in the course of the experiments turned 
black. It was found that when a current of the solution was 
forced upwards these effects could not be produced, and the 
film was not affected when a small body Avas dropped into it. 
When the solution has been exposed to the heat for a few 
hours the film becomes too thick to exhibit the experiment, 
and when cold the appearances described could not be pro- 
duced. This experiment was referred to merely as illus- 
trating the appearances of sun spots, and in no Avay as 
explaining their cause. At the same time it suggested the 
idea that if the luminous photosphere of the sun is formed 
of bodies, named by various observers, “ willow leaves” 
(Nasmyth), “rice grains” (Stone), “bits of straAv” (DaAves), 
and of the existence of distinct bodies of some kind on the visi- 
ble surface of the sun (here can now be very little doubt, they 
