- INTRODUCTION. 
lr we examine the geographical situation of the British Islands in relation to continental Europe, 
we cannot but perceive the advantages offered, as a point of observation to the naturalist, wherein 
to study, among other interesting facts connected with the habits of the feathered race indigenous 
in our portion of the globe, the periodical migrations undertaken by so many species, the time of 
their arrival and retreat from our shores, together with the ends to be answered both by their 
visit and departure. As regards temperature, no less than relative situation, are these islands 
favourable for a series of such observations: we need scarcely say that, placed to the westward 
of Europe, they occupy a medium station between the extremes of heat and cold: no portion 
indeed of the European continent advances within the line of the intertropics; still, however, 
the southern shores of Spain, Italy, and Turkey in Europe, together with the minor islands of 
the Grecian Archipelago, participate so nearly in the temperature of the hotter portions of the 
globe as to present us with many natural productions whose congenial habitat is exclusively 
beneath a sultry sky. But the summer heat of England never rises above a moderate degree of 
‘temperature, and the severities of winter are mild in proportion ; on the other hand, if we visit 
the extreme north of the European continent, we there find a climate, the severities of which 
in winter are extreme, while the summer, though hot while it lasts, endures but for a short 
period. 
We will not attempt to discuss the subject of the universal law of migration further than 
to observe that its immediate intention is the well-being of such species as would be deprived of 
their natural food were they to remain stationary in any given locality ; in addition to which it 
is essential in another point of view, inasmuch as by its operation there is secured both a 
