48 Dr. Herschei/s Experiments on the Means 
remained visible, and were almost as bright as when the sun 
shone upon them. 
I saw one of the globules lose its spurious diameter while 
the sun continued to shine. After some time the spurious dia- 
meter came on again, and very gradually grew brighter, but not 
larger. The colour of one of the globules being of a beautiful 
purple, changed soon after to a brilliant white. 
The sun being obscured by some clouds, a globule lost its 
spurious diameter, and acquired the shape of an half moon, of 
the size of the real disk or diameter of the globule. I saw the 
sun break out again, and the half moon was gradually trans- 
formed into a much smaller spurious disk. 
(10.) The spurious disks of globules are lost for want of 
proper illumination, but do not change their magnitude on that 
account. The brightness of the atmosphere in a line day is 
sufficient to produce them ; though the illumination of the sun 
is generally the principal cause of them. 
(11.) The diameters of spurious disks are liable to change 
from various causes ; an alteration in the direction of the illu- 
mination will make the reflection come from a different part of 
the globule, which can hardly be expected to be equally po- 
lished in its surface, or of equal convexity every where, being 
very seldom perfectly spherical ; but as upon the whole the 
figure of them is pretty regular, the apparent diameter of the 
spurious disks will generally return to its former size. 
15th Experiment , with Drops of Quicksilver. 
At a time of the year when bright sun-shine is not very 
frequent, I found that my silver globules would seldom give 
