mirror beyond it, also inclined, but in the opposite direction to the line of sight. Two rays
of light will therefore reach the eye from each point of the glass; the one has been reflected
from its surface, and the other has been first reflected from the mirror, and then
transmitted through the glass. The glass used should be extremely thin, to avoid the blur
due to double reflections; it may be a selected piece from those made to cover microscopic
specimens. The principle of the instrument may be yet further developed by interposing
additional pieces of glass, successively less inclined to the line of sight, and each reflecting
a different portrait.
I have tried many other plans; indeed the possible methods of optically superimposing
two or more images are very numerous. Thus I have used a sextant (with its telescope
attached); also strips of mirrors placed at different angles, their several reflections being
simultaneously viewed through a telescope. I have also used a divided lens, like two
stereoscopic lenses brought close together, in front of the object glass of a telescope.
II. GENERIC IMAGES.
[Extract from Proceedings Royal Institution, 25th April 1879.]
Our general impressions are founded upon blended memories, and these latter will be
the chief topic of the present discourse. An analogy will be pointed out between these and
the blended portraits first described by myself a year ago under the name of Composite
Portraits, and specimens of the latter will be exhibited.
The physiological basis of memory is simple enough in its broad outlines. Whenever
any group of brain elements has been excited by a sense impression, it becomes, so to
speak, tender, and liable to be easily thrown again into a similar state of excitement. If the
new cause of excitement differs from the original one, a memory is the result. Whenever a
single cause throws different groups of brain elements simultaneously into excitement, the
result must be a blended memory.
We are familiar with the fact that faint memories are very apt to become confused.
Thus some picture of mountain and lake in a country which we have never visited, often
recalls a vague sense of identity with much we have seen elsewhere. Our recollections
cannot be disentangled, though general resemblances are recognised. It is also a fact that
the memories of persons who have great powers of visualising, that is, of seeing well-
defined images in the minds eye, are no less capable of being blended together. Artists
are, as a class, possessed of the