2 PHILOSOPHY OF ZOOLOGY, 
those bodies subject to their influence, they constitute those 
phenomena which the science of Natural Philosophy pro- 
fesses to examine and explain. The instruments of in- 
vestigation employed in this department, like those of the 
astronomer, are measurement and calculation, aided by 
experiment. When the actions which take place among 
bodies, produce a permanent change in their constitution, 
unaccompanied with motions which admit of measurement, 
they are considered as belonging to the Science of Che- 
mistry. Experiment is the only instrument of investiga- 
tion which can be employed with safety in this depart- 
ment. 
When the beings which constitute this terraqueous globe, 
are considered as related to one another, exhibiting par- 
ticular forms, and adapted by their structure to the situa- 
tions in which they are placed, they are regarded as the 
subjects of the Natural Historian. The establishment of 
a System of Nature, to which all his labours are directed, 
can only be completed when all the creatures of the globe 
shall have become known, and their mutual connections 
ascertained. Observation is the peculiar instrument of 
research which he employs. 
All these sciences mutually explain and illustrate one 
another. The doctrines of the one are often employed 
with success, to solve the difficulties which occur in the 
other; and the instruments of the one may be substituted 
for those of the other, in particular circumstances, with 
the happiest results. 
