 Because Humboldt did not mention God in his work "Cosmos", and sometimes spoke unfavourably of religious attitudes, it was occasionally speculated that he was a materialist philosopher, or perhaps an atheist.However, unlike irreligious figures such as Robert G. Ingersoll, who went so far as to use Humboldtian science to campaign against religion, Humboldt himself denied imputations of atheism.In a letter to Varnhagen von Ense he emphasized that he believed the world had indeed been created, writing of "Cosmos"