Sanskrit in Bhagavad Gita

I am reading the book The Bhagavad Gita by Winthrop Sargeant. It is a beautiful book, worth reading by anyone who loves both Bhagavad Gita and Sanskrit. This is what the author notes on on the Chandas used in Bhagavad Gita (Page 8):

The metre of most of stanzas of Bhagavad Gita is what is known as shloka metre, consisting of four lines of eight syllables each. The verse is blank, i.e., there are no rhymes. There are, however, a number of stanzas, particularly at dramatic moments, in which the tristubh metre, consisting of four lines of eleven syllables each, is used. The shloka is the all-purpose metre of Epics as well as much of poetry. The tristubh metre originated as the commonest metre of the Vedas, and is supposed to convey a warlike or powerful impression.

To understand the notion of relationship between chandas and tenor, one should observe chapter 11 (as well as verses 2-5 of chapter 12) of Gita, where most of the core verses are in in "another metre". I agree with all of this, but for the names of the metre "tristubh". I know for sure the following about vedic chandas (from my Vedic Guruji):

Vedic Tristubh 11-11-11-11 = 44
Vedic Anusthup is 8-8-8-8 = 32

The question are: Is this (the chandas of the verses that Winthrop Sargeant is talking about) really tristubh? If so, is it the same as Vedic Tristubh Chandas? If it is so, does it follow the same rules (breaking of the words and the like), as Vedic verses? More importantly, "Which are the verses in the Gita, where the tenor change has been emphasized by change in Chandas? What is the meaning of the change of chandas in these verses?"

So, further research brought me to the beautiful "Sadhaka Sanjivani" by Swami Ramsukhdas. In that book, every chapter has detailed notes on the Chandas used in that particular chapter. It also has other details, like count of number times some words like "uvacha" etc. have been used and further, it has a count of number of syllables in that chapter!

Here is a tabulation of the Chandas in various chapters of the Gita, according to the information in the book:

Chandas in Bhagavad Gita

Ch#	Verses	Vipula	Pv-Anu	Upajati	Misc
1	47	5	42
2	72	15	49	8
3	43	10	33
4	42	9	33
5	29	3	26
6	47	10	37
7	30	7	23
8	28	5	19	3	1
9	34	7	25	2
10	42	6	36
11	55	5	14	33	3
12	20	3	17
13	34	5	29
14	27	7	20
15	20	5	10	3	2
16	24	6	18
17	28	9	19
18	78	19	59

Where
Vipula = Vipula-anusthup chandas of na/ra/bha/ma/sa or jatipaksha or sankirna variety.
Pv-Anu = Pathyavaktra-anusthup.
[Note: Both the above are varieties of Anusthup Chandas.]
Upajati = Upajati
Misc = Indravraja/upendravraja.

So, most of the verses (645/700) in Gita are in anusthup chandas, of the vipula-anusthup variety or pathyavaktra-anusthup variety. The rest of the verses (55/700) are either in upajati chandas (49/700) or in indravraja/upendravraja chandas (6/700).

Here are the various uses of upajati metre

Upajati Chandas in Gita

Chapter	Specific Verses
2	5-8,20,22,29,70
8	9,10,11
9	20,21
11	15-27, 30-44, 46-50
15	2,3,4

and here are the various uses of indravraja/upendravraja

Vraja-Chandas in Gita

Chapter	Specific Verses
8	28 is indravraja
11	28,29,45 are upendravraja
15	5,15 are indravraja

It would be interesting to know why Bhagavan Vyas used these special chandas at these particular places. Is there any deeper meaning to the use of these special chandas? Can someone explain? When asked the same questions on advaitin list, respected Shri Sadaji replies:

Interesting info. My understanding is sloka format normally refers to AnuShTup chandas as you pointed out. AnushTup is easy to follow since it has four quarters, as the emphasis is on the message rather the literature. Since the communication is by word of mouth, the meter is changed whenever some thing has to be emphasized or for registering a change of topic
or to draw attention to some serious point of discussion, where the student's attention is required.
...

In Telugu lot more work has been done with chandas - where the meters (like raagas) are selected to project the proper moods of the characters. But for Vedanta, emphasis is not on emotions but on understanding. anuShTup is simple and best suited and is used extensively.

Read the whole reply. On a related noted, but in another thread posted some time back, respected Shri Sunderji notes:

...
There is a legend about the composition of Mahabharata by Vyasa. Vyasa requested Ganesha to be his scribe for this opus. Ganesha agreed to do it on condition that Vyasa would do the dictation without any interruption. Vyasa accepted it, but put a counter-condition that Ganesha would not write anything that he did not understand! Ganesha too agreed.

Thus, whenever Vyasa wanted to pause for a breather, he would compose a verse like a riddle, that made Ganesha stop and think!!

There are said to be about 3400 such riddles in the @100,000 verse of the Mahabharata.

I have often wondered which some of these riddles may be in the Gita!
...

Read the whole message and the thread. This message leaves the chandas-puzzle, if there was any in the first place, unanswered.

Also, this article from Kamakoti has some more details about chandas.

PS: Here is a place to get a very good quality PDF of Bhagavad Gita.