Parts of this article's biography are based on a translation of an equivalent article at the French Wikipedia.

A Russian translation of an article by Spencer on education was published in 1874.

This article is a translation of an article in the Italian-language Wikipedia.

Parts of the biography are based on a translation of an article from the German Wikipedia.

Parts of this article are based on a translation of an article from the French Wikipedia.

Part of this article are based on a translation of an article from the German Wikipedia.

Biographical information based on a translation of an equivalent article at the German Wikipedia.

Biographical information is based on a translation of an article from the German Wikipedia.

This article is based on a translation of an article in the Finnish Wikipedia.

This article is based on a translation of an article from the French Wikipedia.