It may appear strange that, in these days, when the French language is almost as familiar to English readers as their own, I should have spent many months in rendering into English a work which presents no difficulties of language, and which is undoubtedly known to all philosophical students. Seldom as Comte's name is mentioned in England, there is no doubt in the minds of students of his great work that most or all of those who have added substantially to our knowledge for many years past are fully acquainted with it, and are under obligations to it which they would have thankfully acknowledged, but for the fear of offending the prejudices of the society in which they live. Whichever way we look over the whole field of science, we see the truths and ideas presented by Comte cropping out from the surface, and tacitly recognized as the foundation of all that is systematic in our knowledge. This being the case, it may appear to be a needless labour to render into our own tongue what is clearly existing in so many of the minds which are guiding and forming popular views. But it was not without reason that I undertook so serious a labour, while so much work was waiting to be done which might seem to be more urgent.