112 
HISTORY OF THE 
[1850-60 185 
theory of light and taking the place that he held so long of being pj a] 
the ultimate court of appeal on subjects that were sufficiently jj a] 
difficult to baffle all other enquirers. Just by way of a date point, pj c j 
we may note that the Change of Refrangibility of Light was read ma( 
to the Royal Society in two parts, 1852 May and 1853 June * a 
respectively. in t 
Turning to astronomy, we find that a change no less fundamental i e d 
was coming, and though we should, perhaps, not be justified in j n( q 
claiming for the decade under review its actual arrival, we may pj a f 
confidently assert that, looking back now on these ten years, we see G f t 
in them a period of great development, containing promise of thes 
changes even more profound. Anyhow, it is clear that the outlook 
and aspirations of the astronomer of i860 were of a different nature heli< 
from those of his predecessor of 1850. With the invention of a da 
photography and the discovery of spectrum analysis, the the 
astronomer’s powers were multiplied and the whole scope and it w 
possibilities of his science enormously enlarged. Up to 1850 the unti 
only photographic process known was the daguerreotype, a method ] 
producing pictures of exquisite fineness of detail but demanding thri] 
high technical skill, and moreover requiring exposures of such length mar 
that it was useless as an accessory to the telescope except for the inte: 
sun. The first recorded astronomical photograph is one of the total ther 
solar eclipse of 1851 July 28, for which see volume 41 of the Memoirs , for l 
Royal Astronomical Society. It shows the corona extending from De ' 
the limb for about one-fifth of the diameter of the moon. In 1850 reco 
the collodion wet plate was invented, and a photographic method Com 
with a not too difficult technique and requiring exposures of about of s 
one-thirtieth of those previously necessary was thus placed in the eqm 
hands of experimenters. Sir David Brewster, in his Presidential his 1 
address to the Edinburgh meeting of the British Association held reco: 
in that year, devoted a large part of his time to the subject of with 
astronomy, and said, “ Though but slightly connected with astro- take 
nomy, I cannot omit calling your attention to the great improve- I 
ments, I may call them discoveries, which have been recently with 
made in photography.” This view, that the connection between done 
astronomy and photography was slight, was, however, not shared G. F 
by others, who saw in the new science a most promising addition In b 
to the astronomer’s tools, and lost no time in attempting to bring grap 
it into service. of sh 
An early and successful experimenter was Warren de la Rue, Han 
an esteemed Fellow of the Society who obtained the Gold Medal C 
in 1862 and became President in 1864. He devoted himself with greal 
great energy and at considerable outlay to the construction of a new subsi 
telescope specially designed for this work, and secured numberless The 
very beautiful photographs of the moon, also some of stars and 6-foo