An image of [Greek: alpha] Lyrae was
thus obtained, and for this Mr. Bond received a gold medal at the first
international exhibition, that at the Crystal Palace, in London, in
1851. In 1857, Mr. Bond, then Professor Bond, director of the Harvard
Observatory, again took up the matter with collodion wet plates, and in
three masterly papers showed the advantages of photography in many ways.
The lack of sensitiveness of the wet plate was perhaps the only reason
why its use progressed but slowly. Quarter of a century later, with the
introduction of the dry plate and the gelatine film, a new start was
made. These photographic plates were very sensitive, were easily
handled, and indefinitely long exposures could be made with them. As a
result, photography has superseded visual observations, in many
departments of astronomy, and is now carrying them far beyond the limits
that would have been deemed possible a few years ago.
The third great advance in astronomy is in photographing the spectra of
the stars. The first photograph showing the lines in a stellar spectrum
was obtained by Dr.
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