PREFACE 
AM quite certain that the majority of my read- 
ers would have me always stick to natural his- 
tory themes. I sympathize with them. I am myself 
never so well pleased as when I can bring them a 
fresh bit of natural history, or give them a day with 
me in the fields and woods or along the murmuring 
streams. Birds and squirrels come home to us all 
in a way that speculative ideas do not. While writ- 
ing my more philosophical dissertations, my mind 
often turns longingly toward the simple outdoor 
subjects which have engaged me so many years, and 
doubtless the mind of my reader does also when he 
is perusing them. But one cannot always choose at 
such times. Natural history is a matter of obser- 
vation; it is a harvest which you gather when and 
where you find it growing. Birds and squirrels and 
flowers are not always in season, but philosophy we 
have always with us. It is a crop which we can 
grow and reap at all times and in all places, and it 
has its own value and brings its own satisfaction. 
We are all philosophers, we all delight in finding 
the reason of things and in tracing the relation of 
things, and to know, for instance, what part chance 
plays in our lives, and what part is played by rigid 
law, is a worthy and engaging problem. I do not 
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