120 
THE NATURALISTS’ JOURNAL. 
Lambeth Field Club. —December 18th : A “social evening” 
was held at the Society’s rooms, during which exchanges of 
specimens were made, the specimens themselves discussed, and 
light refreshments partaken of by the members present. The 
promised paper on “ Tin and Lead ” was again postponed ; 
nevertheless, a very enjoyable evening was spent. 
January 8th, 1894: The first meeting of the year was the 
occasion of a most entertaining lecture by Mr. Frank R. Tayler, 
the subject being “ A Ray of Light.” The lantern was used to 
illustrate the lecture, and a number of explanatory diagrams and 
natural scenes were shown on the screen, some of the latter 
being extremely picturesque and exciting much admiration. 
The lecturer began by pointing out that were it not for light 
there would be no life—animal or vegetable—on the earth. It 
was light that produced colour throughout nature, and it was 
light that was directly connected with the sense of vision in our¬ 
selves and other animals. The heavenly bodies were revealed to 
us only by the light they emitted or reflected. The principal 
source of light was, of course, the sun, whose light was one hun¬ 
dred and forty times greater than limelight, and even the darkest 
part of a sun spot was more brilliant than the latter. Light itself 
however, was invisible, and a beam of sunlight was only seen by 
reflection to our eyes from dust particles in the air. The lecturer 
then proceeded to explain the structure of the human eye, which 
he said was made up chiefly of three distinct parts, the aqueous 
humour, the crystalline lens, and the vitreous humour. Light coming 
from an object was converged by the crystalline lens on to a 
screen at the back of the eye, called the reiina, where it came to 
a focus arid a picture of the object was formed, of which we were 
made aware by the optic nerve conveying the fact to the brain. 
Behind the retina there was a coating of dense black pigment, 
which prevented any of the rays of light from being reflected, 
though in some animals, as the cat, there was a structure corres¬ 
ponding in situation, called the tapetum, which did reflect the 
light, and this was why a cat’s eyes shone in the dark. Of course 
this could not happen in total darkness. The analogy between 
the eye and the photographic camera was very evident. The 
velocity of light was first made known by the observations of 
Roemer, who noted the period that elapsed between two succes- 
‘ sive emergences of Jupiter’s first satellite from the shadow cast 
by the planet, through which it travelled in its revolutions. 
Later researches had fixed the velocity of light at 186,000 miles 
per second. Sunlight took about eight minutes to reach us, and 
a cannon ball going at a constant rate of speed’would cover the 
distance in seventeen years. A number of optical illusions were 
explained by reflection. Such was “ Pepper’s Ghost,” which was 
simply the reflection in a sheet of plate glass, inclined a little 
forward, of a person concealed from the spectators. The actors 
