I am most happy to report that I have a transcription of Professor Tauruscat's letter to the Baron, although only the first page has been found. It does reveal much about the purpose of the helmet, and it was found with several pages of scribbled notes and sketches seemingly related to the design of said helmet. I am now thinking that I might be able to build a reconstruction of this wondrous device, based upon this information.
I present the letter herewith.
Baron Henry Balzerhaught
München, Upper Bavaria
My dear sir,
It is with some reticence that I take pen to paper in response to your last missive, not because of any reluctance to share with you—my esteemed benefactor—the information that you have requested, but solely due to my awkwardness in putting my thoughts down on paper. I will be forever grateful sir, for your generous monthly allowance, which enables me to spend time doing the research necessary to the pursuit of applying my discoveries to practical knowledge and the constructing of machines and mechanical devices which can be utilized to further your explorations and other adventures.
Specifically, you have asked about my helmet, and I will attempt to provide you with a detailed perspicuous response. I recognized many years ago that my most creative ideas and thoughts came to me while in a state of light sleep. While others are dreaming, I surmised, I was imagining unknown worlds with wondrous machines. But upon awakening I encountered great difficulty in fully recovering all of my thoughts, and this was most frustrating to me. And so I set out to find a way to amplify and clarify my nocturnal and crepuscular visions so as to be able to bring forth those ideas into my waking world.
I did succeed, as I am sure you recognize, in accomplishing my goal, by constructing a leather helmet which contains multiple sensors that read the magnetic impulses of my brainwaves. These are connected to a central processing engine of my own design which I shall not attempt to explain, other than to say that it draws energy from the aether. Upon awakening I am able to fully remember all of my visions and thoughts as if I had experienced them but yesterday.