From this time onwards I gave all my thoughts to methods of education, whereto I was also further incited by some keen critical lectures on the history of ancient philosophy.  These again afforded me a clear conviction of the soundness of my views of Nature and of the laws of human development.

Through my work at the dynamical, chemical, and mathematical aspects of Nature I came once more upon the consideration of the laws of number, particularly as manifested through figures; and this led me to a perfectly fresh general view of the subject—­namely, that number should be regarded as horizontally related.[84] That way of considering the subject leads one to very simple fundamental conceptions of arithmetic, which, when applied in practice, prove to be as accurate as they are clear.  The connection of these (dynamical and arithmetical) phenomena was demonstrably apparent to me; since arithmetic may be considered, firstly, as the outward expression of the manifestation of force, secondly (in its relationship to man), as an example of the laws of human thought.

On all sides, through nature as well as through history, through life as well as through science (and as regards the latter through pure science as well as through the applied branches), I was thus encountered and appealed to by the unity, the simplicity, and the unalterably necessary course, of human development and human education.  I became impelled by an irresistible impulse towards the setting forth of that unity and simplicity, with all the force, both of my pen and of my life, in the shape of an educational system.  I felt that education as well as science would gain by what I may call a more human, related, affiliated, connected treatment and consideration of the subjects of education.

I was led to this conviction on another ground, as follows:—­Although my friends Langethal, Middendorff, and Bauer served with me all through the war in the same corps, and even in the same battalion, we were a great deal apart towards the close of the campaign, especially at the time we were quartered in the Netherlands, so that I, at all events, at the disbanding of the corps, knew not whither the others had gone.  It was, therefore, an unexpected pleasure when, after a while, I found them all at Berlin again.  My friends pursued their theological studies with earnestness, and I my natural science; therefore, at first we came little into contact with one another.

So passed several months, when suddenly life threw us closer together again.  This came about through the call to arms in 1815.  We all enlisted again together as volunteers.  On account of our previous service, and by royal favour, we were at once promoted to officer’s rank, and each one was appointed to a regiment.  However, there was such a throng of volunteers that it was not necessary for any State officials to be called upon to leave their posts, or for students to interrupt their studies, and we