William Hamilton's celebrated letters, articles and publications embodied his experiences as a direct observer of nature. This paper tracks their different courses through preparation, production, distribution and consumption to expose the networks through which Hamilton's knowledge was made and moved. It makes a detailed study of the changes incurred when his experiences were translated between written, oral, painted and printed formats. Sensitive to contemporary notions of curiosity, it then links these changes to the distinct audiences that each embodiment found. The paper frames each piece as an opportunity for beholders to become virtual witnesses in order to describe people's diverse encounters with Hamilton's work. This model is developed to highlight the agency and diversity of readers and the importance of physical format for the movement of witnessing tools. The exploration of Campi Phlegraei demonstrates how this method of communications study can be a valuable approach to the history of science.