350 Sir John Lubbock’s Address. 
experiments in 1850. According to the undulatory theory the 
velocity of light ought to be greater in air than in water, 
while if the emission theory were correct the reverse would 
be the case. The velocity of light— 186,000 miles in a sec- 
ond —is, however, so great that, to determine its rate in air, 
as compared with that in water, might seem almost hopeless. 
The velocity in air was, nevertheless, determined by Fizeau in 
1849, by means of a rapidly revolving wheel. In the follow- 
ing year Foucault, by means of a revolving mirror, demon- 
strated that the velocity of light is greater in air than in 
water — thus completing the evidence in favor of the undula- 
tory theory of light. 
e idea is now gaining ground, that, as maintained by 
Clerk-Maxwell, light itself is an electro-magnetic disturbance, 
the luminiferous ether being the vehicle of both light and 
electricity. 
iinsch, as long ago as 1792, had clearly shown that the 
three primary colors were red, green, and violet; but his re- 
that there were seven principal colors—red, orange, yellow, 
indi f which — 
be present. 
Helmholtz, however, again showed, in 1852, that a color to 
our unaided eyes identical with white, was produce m- 
of blue and yellow makes green. This, however, is entirely 
a mistake. course we all know that yellow paint and blue 
trace of green, but if pure would produce the effect of white. 
and green, which put an end to the pretension of yellow to be 
considered a primary element of color. From these and other 
