Balfour Stewart 
Physics [PDF ebook] 

Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. In fact you have been told about the various kinds of things we have in the world, but you have not yet learned much about the affections or moods of these things. You are yourself subject to change of moods; sometimes you appear with a smile on your face, and sometimes, perhaps, with a face full of frowns or tears sometimes, again, you feel vigorous and active sometimes dull and listless.