352 Sir John Lubbock’s Address. 
the transmitted light will appear yellowish. But as the sun 
sinks towards the horizon the atmospheric distance increases, 
and consequently the number of the scattering particles. They 
weaken in succession the violet, the indigo, the blue, and even 
disturb the proportions of green. The transmitted light under 
such circumstances must pass from yellow through orange to 
red, and thus, while we at noon are admiring the deep blue of 
the sky, the same rays, robbed of their blue, are elsewhere 
lighting up the evening sky with all the glories of sunset. 
nother remarkable triumph of the last half-century has 
been the discovery of photography. t the commencement of 
the century Wedgwood and Davy observed the effect produced 
y throwing the images of objects on paper or leather pre- 
pared with nitrate of silver, but no means were known 
which such images could be fixed. This was first effected by 
Niepce, but his processes were open to objections, which pre- 
vented them from coming into general use, and it was not till 
1839 that Daguerre invented the process which was justly 
named after him. Very soon a further improvement was 
effected by our countryman Talbot. He not only fixed his 
‘‘ Talbotypes” on paper—in itself a great convenience—but, by 
obtaining a negative, rendered it possible to take off any num- 
ber of positive, or natural, copies from one original picture. 
This process is the foundation of all the methods now in use ; 
perhaps the greatest improvements having been the use of 
glass plates, first sii by Sir John Herschel ; of collodion, 
suggested by Le Grey, and practically used by Archer; and, 
more lately, of gelatine, the foundation of the sensitive film 
now growing into general use in the ordinary dry-plate process. 
Not only have a great variety of other beautiful processes been 
invented, but the delicacy of the sensitive film has been 1m- 
mensely increased, with the advantage, among others, of dimin- 
ishing greatly the time necessary for obtaining a picture so that 
even an express train going at full speed can now be taken. 
Indeed, with full sunlight 44, of a second is enough, and in 
photographing the sun itself of a second is sufficient. 
e owe to Wheatstone the conception that the idea of 
solidity is derived from the combination of two pictures of the 
same object in slightly different perspective. ‘This he proved 
in 1888 by drawing two outlines of some geometrical figure or 
other simple object, as they would appear to either eye respect- 
ively, and then placing them so that they might be seen, one 
y each eye. The “stereoscope,” thus produced, has been 
greatly popularized by photography. hae 
For 2,000 years the art of lighting had made little if any 
tion Until the close of the last century, for instance, our 
ighthouses contained mere fires of wood or coal,’though the 
