In Mormon locution, closing a discourse with the phrase, “in the name of Jesus Christ, amen”, or a variation thereof, is standard practice. However, this practice, as currently employed, is a relatively recent innovation in the Mormon tradition. After having my interest piqued while reading a post on LDS-Phil, I took my down-time on this most recent business trip, and researched the history (1852 to 1970) of this now ubiquitous phrase.

The phrase’s implementations may be categorized quaternarily:

In Blessing
In this usage, the orator invokes the Lord’s name as a conclusion to a blessing (e.g., “I bless you all in the name of Jesus Christ. Amen. JD 8:39). There were only 16 instances of an blessings being used to terminate a discourse in the references searched.

In Supplication
This usage is synonymous to prayer. From the 1850’s on, a minority of discourses were terminated in supplication to the Lord. This practice gained in popularity until the 1940’s, when all discourses were thereby terminated. Examples of usage include: “I pray that God may enlighten our minds, guide our feet in the way of truth, and save us in his kingdom, in the name of Jesus Christ. Amen.” JD 8:6; “May God help us to live the life of a Saint and finally save us in his kingdom, is my prayer, in the name of Jesus Christ. Amen. JD 21:91; and “God help us to treasure this testimony, I ask in the name of Jesus Christ. Amen.” Conference Report, April 1920 pg. 83.

In Testimony
Closing a discourse with a testimony or witness started at the turn of the century, but did not become common until the late 1910’s. An Example of such usage is, “I bear this testimony humbly, in the fear of God, and in the name of Jesus Christ. Amen.” (Conference Report 1920, pg. 46.)

As an Orphan
Starting in the 1950’s, discourses were terminated by stating that the words spoken were “in the name of Jesus Christ, amen” or by sticking the incomplete sentence: “In the name of Jesus Christ, Amen” at the end of the talk.

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Methods
Before, we get into the nitty gritty, I want to qualify the data presented here. The data comes from searching electronic copies (Gospel Link 2001) of:

Journal of Discourse 1-26 (1853-1886)
Collected Discourses 1-5 (1886-1898)
April General Conference Reports (1898-1915, 1917, 1918, 1920-49, 1951, 1953-70)
June 1919 General Conference Report

I did not have 1916, 1950 or 1952 Conference Reports on the computer I travel with. I limited the query to one conference per year, because I’m lazy and tabulated all this by hand. Results are from querying the aforementioned references to find instances of “in the name of Jesus Christ” and “amen” that occur in the same paragraph. Consequently some variations of the closure (e.g., in the name of the Lord Jesus Christ, amen, etc.) were not tabulated.

Results
The vast majority of 19th century Mormon discourses were not terminated by invoking the name of Jesus Christ. Normally a discourse would be terminated by the utterance of “amen”, without the qualifying appellation (e.g., “God bless you all. Amen. JD 10:32). However, invoking the Lords name became more popular with time and by the 1940’s all talks were closed in supplication. Below is time-line of notable occurrences in the history of this usage. Subsequently, graphs are presented (and I know, I should have done percentage of talks given, not frequency – but again, I’m too lazy), and lastly are the references cited in the timeline.

1853 – (1) Parley P. Pratt issues a discourse at the temple grounds in which he terminates in the orphan usage. As this is the only usage for the next 67 years, I tend to think this was a transcription error.
1857 – (2) Heber C. Kimball curses the leaders of the US government in the name of the lord. This is the only instance of “cursing” I found in my query.
1858? – (3) Orson Hyde has the first recorded concluding testimony. This does not happen again until the turn of the century.
1900 – (4) William H. smart delivers the next closing testimony.
1920 – two uses of the orphan (only one other in the next 33 years)
1953 – (5) Bruce R. McConkie is the first to consistently use it as the orphan, but in doing so, he uses, “In the name of Jesus Christ.” as a sentence in and of itself. He continues to be the only one for the next five years to use it as the orphan (however, from there it grows in popularity until the end of the observed period).

The other small line not defined by the legend denotes the occurances blessings.

(1) But remember, O ye Saints of the Most High! remember that the enemy is on the alert. That old serpent and his angels, who have ruled this lower world, with few exceptions, for so many ages, will not tamely, and without a struggle, submit to have the kingdom, and seat of government, and sanctuary of our God, again erected on our planet, no more to be thrown down or subdued, till every square yard of the vast dominion shall be reconquered by its rightful owners. No! From the moment the ground was broken for this Temple, those inspired by him [Satan] have commenced to rage; and he will continue to stir up his servants to anger against that which is good, but, if we are faithful, the victory is ours, in the name of Jesus Christ. Amen.
Elder Parley P. Pratt, JD 2:47

(2) Did I ever wrong them, a man or woman of them, out of a dime? No; but I have fed thousands where I never received a dime. Poor rotten curses! And the President of the United States, inasmuch as he has turned against us and will take a course to persist in pleasing the ungodly curses that are howling around him for the destruction of this people, he shall be cursed, in the name of Israel’s God, and he shall not rule over this nation, because they are my brethren; but they have cast me out and cast you out; and I curse him and all his coadjutors in his cursed deeds, in the name of Jesus Christ and by the authority of the Holy Priesthood; and all Israel shall say amen.
Heber C. Kimball, JD 5:34

(3) This is my testimony, and the testimony of the living God through his Apostle to all connected in the name of Jesus Christ; and the Spirit beareth record. Amen.
Elder Orson Hyde, JD 7:53

(4) The spirit bore witness to us that that word was from God and that it was not of man. I do not feel that I have power to take up your valuable time this morning, but I did want to bear this testimony unto you, and I do it in the name of Jesus Christ. Amen.
William H. Smart, Conference Report, April 1900, Third Day—Morning Session 50.)

(5) There is no greater gift that a person can earn and enjoy for himself, in mortality, than the gift of the Holy Ghost, which gift is the right to the constant companionship of that member of the Godhead, and which gift is actually enjoyed only on condition of individual righteousness.
In the name of Jesus Christ. Amen.
Bruce R. Mcconkie, Conference Report, April 1953, Second Day—Morning Meeting 76.)