The Author seems to have passed away as per this and other sites on him.
I am afraid that is not really relevant. However, if the heirs want to submit the book for PG, that should be possible. Also, there is currently a movement afoot in the US (initiated by the US Copyright Office) to liberate orphan works. However, it may take a couple of years before PG can legally publish these works. If you are planning to submit books to PG, please read the FAQ first. You can find it at <http://www.gutenberg.org/faq/C-10.php>. It is a hefty document, but it does have most of the answers, and is easy to read. Also read the Copyright Howto: <http://www.gutenberg.org/howto/copyright-howto> Even if you are not planning to submit books, reading a FAQ is always the polite thing to do before you enter a conversation.
Steve, the Author of the site soliandearth.org is confident that this book is Public Domain.
That is not how I read his reply, but perhaps he can elaborate. -- branko collin collin@xs4all.nl