The person who has re-published your relative's work is no doubt relying on American copyright law when it comes to determining if the original work is still in copyright. The system in the USA changed in 1976 from one where a work had to be registered to gain copyright protection, to the system today which is pretty much the same as has been the case in the UK for several centuries, namely that copyright exists for any original work from the moment it is recorded in some permanent form, and the length of protection is based on the lifetime of the author followed by a post mortem
period which has varied over the years.
The US 1976 Copyright Act included some relatively complicated transitional arrangements for works which were already in existence, including works made by foreign authors. Fortunately Cornel University Law School has produced a useful guide
for determining whether or not a work is now in the public domain in the USA. If you scroll down to the section headed 'Works First Published Outside the U.S. by Foreign Nationals or U.S. Citizens Living Abroad' you can see the various options laid out. Where it talks about formalities, these include the requirement that a formal notice of copyright is included in the work; it is has been registered and the registration renewed at the end of the initial 28 year period, a copy of the book was deposited with the Copyright Office at the Library of Congress; and the manufacture of the US edition was done there. Your relative's book will almost certainly have had a copyright notice (which is pretty standard, though not mandatory, in the UK), but it may well be that it was never registered in the USA, and if so, it is even less likely that a separate edition was printed there. This latter provision was a form of protectionism intended to provide work for the US printing industry.
So if I am right in my assumptions, the likely category is: 1925 through 1977 - Solely published abroad, without compliance with US formalities or republication in the US, and not in the public domain in its home country as of 1 January 1996 (see my penultimate paragraph about this aspect). As you can see the copyright term would be 95 years from the date of first publication, so in this case, protection would last until the end of 2042.
However if you think the book might have been published in the USA and met some or all of the formalities, then obviously one of the other categories will apply. If you have lots of patience (as a family historian, you probably do) then you can search through the past registration records of the Copyright Office which you can access via the Internet Archive here
. However it may be easier to access the records after first visiting this portal
. If you find that the book was registered in 1947, you then need to check if re-registration occurred 27 years later.
The worst case scenario would be that the book was first registered, printed and published in the USA in 1947, but that the registration was not renewed in 1974/5, meaning that the book would now be in the public domain in the USA. Only around 12% of books from this period had their registration renewed.
Looking briefly at the status of the UK copyright, since the work was published in1947, the period of protection would have been the lifetime of the author plus 50 years from the end of the year of death, which takes us to 3I December 2010. However as the book was in copyright on 1 July 1995, it will have benefitted from a 20 year extension to the post mortem
period (so 70 years after death) which came into force that year. This means that the book will now not enter the public domain here in the UK until 1 January 2031. Incidentally, whoever is the heir to your relative's estate may
possibly be owed some royalties or public lending right payments which have accrued since the death of the author; you or they can check with the Authors' Licensing and Collecting Society (ALCS)
if this is so.
It therefore appears that in all likelihood, the republication is an infringement. What remedies are available is a different topic which I can cover separately if you want me to.