I’ve put together the “case” for the Duffin-Carling polygamy as an exercise in diary reading. (For the previous installment, see here.)
“Amelia B. Carling, missionary from Utah” arrived in the mission, and first appeared in Duffin’s diary, in June, 1901. His notes about her are favorable but routine: she participated in meetings, spruced the office, proofread a publication, and so on.  They often traveled together on mission business, but almost always with a group. 
The diary turns cryptic in 1902 August. Above the Aug 06-09 entries Duffin wrote, “The past few days have been full of important events in my life.”  On the 6th he went to “meet a friend at Pueblo, Col,” but en route received a “telegram…signed by ‘Matthew Foster’ reading: ‘must go south instead of north.’” His “friends” were not in Pueblo so he decided to leave the next day, “asking the Lord, to overrule it according to His will.” The “friends” came, which was “the second test by which I know it is the will of the Lord that he should be here on the important mission for which he has come out.” Duffin continued that “[t]he other test was that one of the missionaries – a, b, c, and myself took a day of fasting and prayer, and asked the Lord if it were His will – that my friend might come, if not that he should not come. I, therefore, now know of a surety that it is the will of the Lord.”  Duffin’s next dated entry is Aug 16 in Chicago; on Aug 26 he reported that Sister Carling and her companion attended a “priesthood meeting.”  I will argue below that Duffin went to Chicago a twice-married man.
Six weeks after the trip to Colorado, “Sister Amelia B. Carling was released, having filled a good, faithful mission.”  After a farewell reception, “Sister Carling and self took train for Salt Lake City,” where Duffin visited with the First Presidency, he and Carling spoke at a mission reunion, and he attended general conference.  Duffin then stayed with his family in Toquerville, Utah, for three weeks, recording at the end that “During my visit home, I have made my wife, Mary, fully acquainted with the important events in our lives of the past few months.” 
In May 1903 Duffin met Carling in Salt Lake and accompanied her partway to Colonia Dublan, Mexico, where she set up house.  At the end of September Duffin went to see “Amilia and sweet little Erma This is the first time I have seen baby. …During the day I blessed baby and gave her the name of Erma, she was born at Colonia Dublan, State of Chihuahua, Mexico July 2, this year 1903”—nine months and two weeks after Carling was released as a missionary. 
Based on the diary, Duffin and Carling corresponded, at least in 1904, and visited two or three times per year from 1902 on. He reported renting and tending property for her use, arranging for household goods, and participating in local social life with “Amelia” or “A.” when he visited.  Beyond recording the circumstantial paraphernalia of a married couple, Duffin also expressed more explicit sentiments: “The Lord has blessed me exceedingly with faithful wives and children.”  On 1904 Feb 19 Carling gave birth to a son and, a week later, “Amelia’s baby was blessed by Apostles John W. Taylor, M. F. Cowley and self, Brother Taylor, being mouth.”  For the 1905 December visit, Duffin reported that Carling came over from Arizona. In 1906 May Duffin “met A— …on her way to Utah” and then went “home” to Provo while “A.- went on to Salt Lake where she will stay for the present.  With that, the diary falls silent on Carling and then ends a few months later with Duffin’s release, ostensibly—and plausibly so—for health reasons. 
Throughout all of the above, Duffin visited his wife, Mary, in Utah, used expressions of affection toward her, noted her feelings with concern, and recorded exchanging gifts.  Their eleventh child came in 1903 December, five months after Amelia gave birth to Erma. 
All together, I think the evidence of the Duffin-Carling marriage in Duffin’s diary is persuasive.  However, I’m not sure when the scales tipped; at some point Duffin changed in my perception from the nice man who happened to visit nine months before children were born to the husband. When? I don’t know. He went to the colonies before, so why do the later trips make me think “conjugal visit?” And why not bless the child of one of his returned missionaries, like Elder Cowley did for Matthias? Evaluating the evidences individually, the strongest conclusions we necessarily draw are that Duffin was a polygamist and that he had a close relationship with Carling. To put the two together we must look to the pattern of evidences, shave with Occam, and/or find external corroboration.  Absent other sources, our interpretation becomes a matter of imagination. I could say that “marriage is the only reason non-philandering, Mary-loving Duffin would have spent so much time with Carling.” What I would mean, though, is “I have not imagined any other plausible scenarios.” Fortunately there are other documents.
For the August trip to Colorado described above, I propose Apostle Matthias Foss Cowley as the “friend,” Amelia B. Carling as “a, b, c,” and that Duffin and Carling married 1902 Aug 12 in Mexico. The entries themselves are merely suggestive on these points: Duffin’s “important events” phrase, his trepidation, and the “south” telegram are consistent with an illegal marriage, in Mexico, that week, and the initials match for Matthew Foster/Matthias Foss Cowley and a,b,c/Amelia B. Carling.  Further, a statement by the “friend” matches a statement later attributed to Cowley; my subjective impression is that Duffin would not have had un-married sex; and the first pregnancy’s timing suggests marriage before mid-October. 
External documents clad the case in iron: a Temple Department marriage record naming both Carling and Duffin provides the time and place and Cowley later reported officiating a polygamous marriage for Duffin.  The 1910 census lists “Glendill” and “Amelia” Duffin as husband and wife, with two children, in Salt Lake City. That same year, “Jas. G.” and “Mary” Duffin appear, also as husband and wife, in Provo living with eight children. In Provo James is a real estate agent; in Salt Lake City he is a “laborer” at “odd jobs.” In 1920, “Amelia Duffin” appears in Bountiful as a widow with three children, the youngest aged six—which puts James and Amelia’s relationship lasting at least until 1913. James and Mary are in Salt Lake City with five children at home, the youngest aged eleven.  James died in 1921, just shy of 61; the only source I have on Amelia puts her dying in 1928 at about 50; Mary died in 1932, aged 69. 
I conclude that James Gledhill Duffin and Amelia Barbara Carling were married in the full conjugal sense and that their marriage overlapped Duffin’s marriage to Mary Jane Grainger for at least a decade. And if I weren’t writing about diary reading, I would have started with the marriage record.
 First mention: 1901 Jun 16; Companion: Sister Sarah Giles of Provo (1901 Nov 09); Cleaned office: along with two local sisters she “cleaned the office building and put up low curtains, which makes the office more comfortable” (1901 Sep 11); meetings: “went on the streets with the Elders and sister Carling and held a fine street meeting” (1901 Sep 11); “Sisters Cannon, Hyde and Carling spoke very interestingly to the sisters and gave much valuable instruction” (1901 Sep 16). “Very excellent instructions were given by Sister Cannon and Hyde and Carling” (1901 Sep 22). “public meetings were held at which spirited addresses were made by the Elders and the lady missionaries” (1902 Sep 14); activity committee: “to get up a Christmas eve entertainment” (1901 Dec 16); Book of Mormon proofreading: 1902 Feb 03; “those who have been assisting me have been very faithful in their labors. My two chief assistants have been Amelia B. Carling and Sarah Giles, who have been devoted to their work. The Elders have responded nobly to the support of the work” (1902 Mar 26).
 Just the two of them: “To day, accompanied by Sister Carling who is going to attend the relief society conference at St John, I left Kansas City” (1901 Sep 12). The trip lasted eleven days but they were joined by several other people; other travel: 1902 Mar 16, 30, 1902 Jun 18 (trip to Adam-Ondi-Ahman involving President Duffin, his wife Mary, the Sisters, and two Elders). Obviously, any statements about them being alone depend on what Duffin wrote.
 The 1902 August entries are the first entries in a new volume of the diary. The last entry in the previous volume was June 20. The August 06-09 entries appear to have been written after the fact, witness the prefatory “The past few days…” and in the Aug 09 entry, the statement, “a few days later he reconfirmed it.”
 1902 Aug 06–09. I don’t have an explanation for the switching between singular and plural friend(s).
 He visited with missionaries and members en route to the Trans-Mississippi Commercial Congress in St. Paul, MN. As part of the trip he also visited Nauvoo. The next entry in Kansas was Aug 26.
 “Sister Amelia B. Carling was released, having filled a good, faithful mission of fifteen months durration. I pray God to bless her that she may have a life of usefulness and happiness. Sister Carling is the first lady missionary who has been in the mission for this length of time” (1902 Sep 21).
 Reception: “All the Elders, and Saints and friends met at the office to give Sister Carling a farewell reception. The Elders presented her with a beautiful gold ring with opal and ruby setting, and the Kansas City relief society presented her with a fine fruit tray. The evening was spent in speeches, songs, recitations &c and refreshments were served to the guests” (1902 Sep 23). Upon arrival in SLC (Sep 29), Carling “went out to Ogden to visit her relatives” and Duffin met his sister, Anna, but “On account of Oreon being so bitter against me, I did not stay with Sister Anna, but went to the White House” (The White House was a hotel). I conjecture that a possibility Oreon, presumably Anna’s husband “Oscar,” is bitter is the second marriage. There are, of course, a multitude of other possibilities. First Presidency: 1902 Oct 03. Duffin only mentions a proselyting tract as being discussed in the meeting. Reunion: 1902 Oct 08. Duffin lists her as “Amelia B. Carling returned missionary.” Lodging: 1902 Oct 08. With caveats about leaps of fancy, when Duffin wrote that he stayed “a portion of the time…at Sister Horker’s. I feel very grateful to her for her kindness to me and others,” I bet “others” meant “my new wife.”
 Toquerville is in southern Utah near Saint George. Duffin makes journal entries for Sep 29, Oct 03, 08, 11, 12, and 30. He does not mention Carling or leaving Utah; “fully acquainted” (1902 Oct 30).
 1903 May 08, 12, 16, 18. Apostle Cowley and others also made the trip. Duffin was called away on a mission emergency so he arranged for Amelia to go on to Dublan without him.
 1903 27, 29 Sep. Carling was released 1902 Sep 21. In the transcription of the Duffin Diary available at BYU’s “Mormon Missionary Diaries” website, the baby’s name is given as “Emea.” Later usage in the diary, external records, and examination of the original all suggest “Erma.”
 Correspondence: 1904 May 13, Jun 20, 29, Jul 02, 22, Aug 30, Dec 24; Visits (always Duffin visiting Carling): 1903 Sep 27–29, Nov 14–23, 1904 May 19–30, Nov 22–Dec 03, 1905 Feb 18–Mar 04, May 09–17, Dec 21–29.
 1905 May 30. Also, after visiting with Carling, he felt “very grateful…for the blessings that the Lord has bestowed upon those whom He has given me” (1903 Nov 23); “those whom the Lord has given me” (1905 Dec 25); “our children” (1905 May 11).
 The birth comes nine months after the 1904 May visit. “He was given the name of Matthias Alma, the first name for Brother Cowley, the second for Alma, the Nephite prophet” (1904 Feb 26). We might read Duffin’s description “Amelia’s baby” as distancing language. However, the following year, 1905 May 11, he refers to “our children” as he records leaving the colony.
 1906 May 22–30.
 Duffin mentions his declining health more than once in the diary; like most of the missionaries, he had recurrent malaria. In the letters exchanged between him and the First Presidency about his release (which he did not request and claimed to be surprised by), his health is the major topic of discussion. Hence the plausibility. However, as the tide turned ever more inexorably against polygamy, the church began to quietly release polygamists from positions of authority. The timing of President Duffin’s release is consistent with the gentle purge of polygamists. Hence my use of “ostensibly.”
 The expressions of affection and concern are pervasive. Some examples include: “It is becoming quite a trial to my dear, faithful wife, Mary, for me to leave home” (1904 Oct 31); “The parting with my wife was very affecting” (1904 Dec 29).
 1903 Dec 19.
 He writes of “wives”; he systematically visits “A. and the children” in Mexico and is grateful “for those whom the Lord has given me”; he refers to “our children”; he and Carling go out in public together; he blesses the infants; he refers to Carling by her first name and almost every other non-family female by their last. A few other tidbits mesh with the idea of a polygamist Duffin. He was close with Apostles Woodruff, Taylor, and Cowley, all post-Manifesto polygamists. (There are several instances, e.g., 1905 Feb 18–Mar 04, 1905 Nov 25). In 1901 Duffin went to Colonia Juarez, staying with Anthony Ivins, another prominent polygamist, and in December of that year took up Spanish, possibly suggesting a planned future in the colonies (1901 Jul 21; this trip was a month after Sister Carling arrived, but I don’t see any evidence to support specific plans for Carling; 1901 Dec 16).
 We must also assume that Duffin was hiding some information but not all of it. That is, we must assume that Carling, Amelia, and A. are the same person, that she was not a cover for a different marriage in the colonies, and that the colonies were not a ruse concealing a second family somewhere else. In short, we have to assume that Duffin’s diary merely excludes information and does not fabricate it.
 Also, Duffin’s phrase, “prophet of the Lord,” could indicate apostles, who were designated as “prophets, seers, and revelators,” thought it could also refer to anyone with the spirit of prophecy, so the usage is inconclusive. Additionally, Duffin’s phrasing to Mary, “past few months” instead of “last month” (1902 Oct 30), supports the idea of an August wedding.
 Duffin wrote in the Aug 09 entry: “my friend made this promise to me: He said: ‘You will never again be cramped for or worried about means’. A few days later he reconfirmed it. I know this will be fulfilled, for I know he is a prophet of the Lord” (1902 Aug 09). Two years later Duffin wrote that “To-day Brother Cowley made me the promise that I should be ‘blessed with an abundance of means.’ This is now the third time he has made a promise to me of temporal blessings” (1904 Jul 19). The 1902 promise(s) by the “friend” could be one (or both) of the previous instances, so Cowley could be the “friend.” Erma Duffin was born 1903 Jul 02 so, ignoring the possibilities of non-wedlocked conception or premature birth, the wedding was in early October at the latest.
 International Genealogical Index v5.0, Mexico, “Amelia Barbara Carling,” spouse, James Gledhill Duffin, married 1902 Aug 12, Juarez, Chihuahua, Mexico. Batch Number: T999279, Sheet: 00, Call No. SIS, Type: Book, www.familysearch.org, accessed 2008 Oct 31. The source note says, “This source has limited access. Direct descendants can contact: Temple Department, Special Services, 50 E. North Temple….” At his disciplinary court in 1911 Cowley was asked about plural marriages he had performed: “…As to Mission Presidents, Brothers Rich, Robinson and Duffin are the only ones I have married.” Hardy cites the transcript in Solemn Covenant as “Trials” but does not identify a specific publication. I am not familiar with the reliability of the version I found on Google. “The Trials of Apostle John W. Taylor and Matthias F. Cowley,” Doctrine of the Priesthood 4, no. 1 (1987): 26. Quinn (1985) cites Cowley’s “Marriage Record,” but I have not examined that document.
 Census access provided by HeritageQuest Online. For the 1910 census showing James living with both wives, the enumerations were Provo, Apr 27, and SLC, May 04-05, respectively.
 James and Mary’s information comes from “Utah Death Certificates, 1904-1956,” from pilot.familysearch.org, accessed 2008 Oct 31; Amelia’s information comes from IGI, with the usual caveats about reliability.