PREFACE 
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knowledge of Nature, especially of ornithology, 
which had become his favourite study. 
Besides much other scientific literary work, he 
published during that period the first three volumes 
of his History of British Birds; and he revolutionised 
the science of ornithology, by insisting on the 
necessity for taking into account, in the classifica¬ 
tion of birds, the internal as well as the external 
organs, to which latter all ornithologists had, up to 
that time, restricted their attention for purposes of 
classification. 
In 1841 he obtained the position of Professor 
of Natural History in Marischal College, Aberdeen, 
which he held until his death in 1852. During 
that period he devoted himself with untiring energy 
and zeal to the discharge of his professorial duties. 
He was a most attractive teacher, and many, 
students were drawn to his lectures, although the 
subjects of them were quite unconnected with 
their own special courses of study—brother pro¬ 
fessors even being unable to resist their attraction, 
while one of them enrolled himself as a student in 
his class. 
In his excursions with his students he taught 
them how to look at Nature in every aspect and 
detail of it, while he inspired them with much of 
his own spirit as a devoted lover of every natural 
object on which they looked, however small or 
apparently insignificant. 
What a blank he left behind him when he 
died! How great the loss was to all who had 
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