A recent post here critiqued an attempt to explain the origins of the book of Ether based on inspiration from a rare book, A Key to the Chronology of the Hindus from a man named Alexander Hamilton (not the US statesmen). After substantial revision, my post was just published on the Interpreter Foundation's blog as "Was a Rare Book on the Hindu Religion a Source for the Book of Ether?" To my surprise, a comment was posted there suggesting a more relevant book from Alexander Hamilton. It turns out this was yet another Alexander Hamilton, a Captain Alexander Hamilton who had experience in the "East Indies," including India. He published his story in another large book almost a century before his namesake's book on the Hindus came out. It's actually relevant to the Book of Mormon in a couple of ways.

Here is the comment made by someone posting as "RM":

Now that sounds much more interesting than what one can find in the later Hamilton's book, which is frankly a very poor candidate as a source for the Book of Mormon. Captain Alexander Hamilton first published his book in 1723, with some later editions. The 1744 edition is available at Google Books: https://www.google.com/books/edition/A_New_Account_of_the_East_Indies/-jNagGDT-PsC?hl=en&gbpv=1. Was A New Account of the East Indies available in the US for Joseph Smith the bookworm to access? Or could it at least have influenced his technical advisory team or Joseph's broad circles of literati? 

Unlike the later Hamilton's book, which wasn't widely distributed even in England where it was published, this earlier book had made it to the shores of the US by 1830 since the 1830 catalog of the library at Harvard shows it listed. However, it still may have been rather rare, for the Library of Congress, building upon Thomas Jefferson's vast library, did not obtain the book until 1904, based on my query with the extremely helpful Rare Books Collection team (email received Dec. 15, 2020). It wasn't in the noteworthy Rochester City Library in 1839. The 1821 catalog at the very large library of Allegheny College also fails to show this book. But at least we know that Harvard had it, so it's possible that Joseph's better educated farmer friends knew all about it, though given that its topic that would seem to have no value for Joseph or his peers and given the few words of material that intersects with Book of Mormon issues, it's unlikely this had any impact on Joseph and his environment. But if Joseph did read it, what would he have gleaned?

In discussing travels to India and beyond, the book raises the issue of the diaspora of the Jews on pages 323--325 (1744 edition), and mentions that some Jews in India said to be descended from the Jews who were carried away to Babylon during the Exile had a tradition about preserving their history on metal plates. Jews writing their history on metal plates? I've heard that somewhere before....

There is now a good body of evidence showing that other Jews and Semitic peoples had put various writings on metal (see https://scholarsarchive.byu.edu/cgi/viewcontent.cgi?article=1695&context=msr), but it was a source of mockery in Joseph’s day. For that Jewish colony in India, I don’t know what became of their recorded history on metal plates, if they really had one — there may be a sacred treasure waiting to be revealed sometime soon, for all I know — but the Jews of the colony appear to have had at least one important document on metal plates, an engraving of a royal charter for their colony from the king of Kerala about 1000 years ago and at least a replica of the plates still exists. See "Jewish Copper Plates of Cochin," Wikipedia, https://en.wikipedia.org/wiki/Jewish_copper_plates_of_Cochin. More on that issue in a moment.

Here is the relevant passage in Captain Alexander Hamilton’s book on p. 324:

They [the Jews in Cochin, India] have a Synagogue at Cochin, not far from the King’s Palace, about two Miles from the City, in which are carefully kept their Records, engraven in Copper-plates in Hebrew characters; and when any of the Characters decay, they are new cut, so that they can shew their own History, from the Reign of Nebuchadnezzar to the present Time....

They declare themselves to be of the Tribe of Manasseh....

While we don't know the details, this at least suggests that in a colony founded by ancient Jews there was an old tradition about preserving important documents on metal. Interesting.  Also interesting is the connection to the tribe of Manasseh, part of the tribe of Joseph, giving another connection to the Book of Mormon.

RM also offered a link to a source in India raising questions about the authenticity of the royal charter on copper plates. See "Few Translations of the Jewish Copper Plates and the Doubtful Authenticity of the Plates," Geopolitical Strategic and Security Studies Institute (GSSSI), India (no date). This reviews the history of the plates with the purported royal charter on them, discusses attempted translations, and raises questions about their authenticity. The focus is on Claudius Buchanan, who visited Cochin decades after Alexander Hamilton and allegedly purchased the plates with the royal charter and had a replica made. The replica had engravings on one side of two plates, while the original allegedly had both sides of a plate engraved. Here is an ancient drawing made of one part of the plates:

Jewish copper plates of Cochin (plate I, side I), a photo of 2-D artwork created before the 11th-century CE. Royal charter issued by the Chera/Perumal king of Kerala, south India to Joseph Rabban, a Jewish merchant magnate of Kodungallur. The charter shows the status and importance of the Jewish colony in Kodungallur (Cranganore) near Cochin, India. There were 28 lines on three sides of two copper plates dating to the early 11th century AD. Script: Vatteluttu (with Grantha/Southern Pallava Grantha script) Language, an early form of Malayalam. Courtesy of Wikimedia Commons, Wikipedia, "Jewish Copper Plates of Cochin."

What happened to the plates? Were there ever real plates? Is it all just some kind of joke or fraud? GSSSI has many doubts, but, as shown in the paragraph below, they strike me as having a rather strong bias when they interpret the University of Cambridge's answer to their query as evidence of the "non-existence or loss of the original brass plates" when it seems that the reply simply means the University hasn't done any research on the plates yet. Plates that have a manuscript number in a university catalog is not the normal way of treating items that simply don't exist:

Buchanan writes in his Annual Report that the plates were originally in brass of which he made copper facsimiles. The original was engraved on both sides while the facsimiles were on two separate plates. He mentions that these plates were deposited in the Public Library at the University of Cambridge. But Thoufeek Zakriya, a researcher, mentions that in response to his inquiry to the Cambridge University, Ms. Catherine Ansorge, Head of Near Eastern Department, (manuscripts and printed Collections, Cambridge University Library) replied by a personal mail about the MsOo.1.14, Charter of Jews of Cochin, which was submitted by Dr. Claudius Buchanan stating “Oo.1.14 -- the texts are all written on rectangles of copper. I do not know of any studies which have been carried out on these” thus confirming the non-existence or loss of the original brass plates even in the Cambridge University or it is that the original brass  plate was never deposited by Claudius Buchanan but instead what he deposited was a copper facsimile. Buchanan also writes that the plates were taken to London. Does the brass plate still exist in London and if so in whose possession and why it has to be kept secret even from Indian historians is a ‘mystery’ yet to be solved.

Meanwhile, multiple studies have been published on the plates and scholars seem convinced that these are real, ancient, and non-fraudulent. See the Wikipedia article cited above and its sources, as well as the following: 

1.  Barbara C. Johnson, "New Research, Discoveries and Paradigms: A Report on the Current Study of Kerala Jews" in Indo-Judaic Studies in the Twenty-First Century, ed. Nathan Katz et al. (New York: Palgrave MacMillan, 2007), 129-146, online at https://link.springer.com/chapter/10.1057%2F9780230603622_8. Here is an excerpt from pp. 129-130:

Fresh historical insight into the early Jewish community in Keralahas emerged from new publications by the esteemed Kerala historian M. G. S. Narayanan, professor and head of the Department of History Emeritus at Calicut University. More than thirty years had passed since the publication of his definitive analysis of the eleventh century Jewish copper plates, still a basic source for all scholarship in the field, when his very welcome renewal of interest in the Kerala Jews was marked by participation in two scholarly gatherings, in Oxford in 2002 and in Israel in 2005. In a 2003 article, he once again turned his scholarly attention to the copper plates, enriching his earlier analysis of their sociopolitical context, and in 2005 he analyzed the leadership position of copper plate recipient Joseph Rabban in the context of eleventh century Kerala society and politics. Both these papers drew extensively from and expanded on material and analysis in his recently published monumental study on Kerala in the ninth to twelfth centuries, Perumals of Kerala. It is hoped that this volume will soon be published for wider circulation.
 

In addition to the important work in this volume by Chakravarti and Weinstein on ancient and medieval contacts between India and Jews in other lands, mention should be made of a 1992 article by the Israeli scholar MeirBar Ilan, exploring contacts between the Jewish communities of Yemen andSouth India. This study is based on interpretation of the controversial eigh-teenth century Cochin Jewish chronicle “Maggid Hadashot,” which is unusual in locating the origin of the Kerala Jews in Yemen. Bar Ilan relates part of its contents to similar eighteenth century Hebrew compositions from Yemen about the history of the Yemenite Jews. He then investigates the possibility that at least some of the manuscripts which are mentioned in the chronicle were actually copies of ancient “lost” apocryphal books, preserved in Yemen and brought to Kerala at a much earlier time.Whatever questions there might be about his analysis of the origin of the chronicle and of the “lost books” mentioned in it, Bar Ilan’s article is valuable in its identification of sources on early contacts between Yemen and Kerala. This topic is of particular interest to scholars exploring Yemenite liturgical and musical influences in Kerala, and to those examining Malabari alternatives to the “Joseph Rabban/Cheraman Perumal/Kodungallur” legends, as found in several other Cochin chronicles and at least one Malayalam folksong.

2. M. G. S. Narayanan, "Further Studies in the Jewish Copper Plates of Cochin," Indian Historical Review, 29/1–2 (Jan. 2002):19-28, online at http://www.mei.org.in/uploads/jijscontent/59-1534436177-jijsarticlepdf.pdf.

Narayanan explains that the language on the plates is consistent with other engravings in that part of India anciently and follows unusual ancient patterns in which dates were sometimes split up, perhaps out of superstition. Such elements are subtle indications of authenticity and antiquity.

It's interesting that engravings on both stone and copper in that part of India were part of the local elite culture anciently. Did the Jewish tradition of engraving on metal influence their environment, or did the Jewish interest in metal engravings derive from their environment, or were both independent? I'm not sure and would appreciate your input if you're familiar with this issue.

In any case, while the 1821 book of Alexander Hamilton on the Hindus is not of much interest for understanding Book of Mormon, a Captain Alexander Hamilton almost a century earlier had one brief section in his large book that hints at what we know from other sources: some ancient Jews may have had a tradition of recording scripture and their own history on metal plates. In spite of his brief hint on this topic, the idea of ancient Hebrews writing on metal plates was widely mocked in Joseph's day and was not part of common knowledge in Joseph's environment. 

Also of interest is the connection of the Cochin Jews to the ancient Jews in Yemen, some of whom Lehi and his family may have encountered, especially when they came to the place that others, perhaps local Yemeni Jews, called Nahom, likely in the region of the tribal lands for the ancient Nihm tribe of Yemen. That region is about 25 miles north of Sana'a and in just about the only place where one can leave the general scope of the Incense Trail and turn nearly due east with a chance of surviving and not only reaching the coast of Oman, but reaching the miraculous but real place called Bountiful. 

For Lehi's family, meeting a group of Jews at Nahom would have been a miraculous blessing that would have made it possible to give a proper Jewish burial to Ishmael, whose burial at Nahom is recorded in 1 Nephi in the Book of Mormon.  Note that Captain Hamilton is not aware of the Yemen connection and writes that the Jews of Cochin fled from Babylon after the Exile. But if they were from the Northern Kingdom, as suggested by their tribal affiliation, they might have been part of the many Hebrews who fled the Assyrian invasion by going to Yemen. Perhaps some later sailed from there for India?

There's much to explore here. I'm grateful for the kind leads provided by RM and welcome any further information you may have. 

Here are some images the Library of Congress kindly sent me of two of their copies of Captain Hamilton's books in their Rare Books Collection, both showing acquisition long after Joseph Smith's day. Beautiful books! And they come with a tiny treasure that intersects lightly with our  Book of Mormon and hints at further treasures to uncover.