What idiom was used before "to be on the same wavelength"?

Question

The word wavelength has the figurative usage with allusion to radio reception, implying (mutual) understanding especially in the idiomatic phrase to be on the same wavelength (as someone else).

What idiom was used before "to be on the same wavelength"?

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OED's earliest citation for the figurative usage of wavelength is from 1927:

Have one's wave length, know one's sentiments.

_{American speech (American Dialect Society)}

Another idiom that comes to mind is to be on the same page but interestingly it has a later original date than to be on the same wavelength in OED:

‘He..finally told me what page he was on’. ‘Is it th' same page you thought it was?’]

_{1965 H. Rhodes Chosen Few 179}

OED gives a cross reference to the following idiom from the idiom to be on the same page:

to sing the same song (also tune) and variants: (of a number of people) to express the same view, to say the same thing; (also, esp. in to sing from the same hymn (also song) sheet) to present a united front, esp. by being seen publicly to agree. Freq. in political contexts.

The idiom singing the same song predates both idioms mentioned above but the meaning and the usage are a bit different.

Here is OED's earliest citation from 1846:

Priests, greybeards, Braccios, women, boys and spies, All in one tale, each singing the same song, How thou must house, and live at bed and board.

_{R. Browning Luria iv, in Bells & Pomegranates No. 8. 15/2}

Can we say that to sing the same song is the earlier form of to be on the same wavelength? or is there any other idiomatic phrase that was used in the past for the same meaning (perhaps along the same lines of the idiom to be on the same wavelength where there is a figurative usage)?

Answer 1

The idiom "of the same mind" long predates "on the same wavelength."

...complete my joy by being of the same mind, having the same love, being in full accord and of one mind. [Philippians 2:2, ESV]

Answer 2

I’m sure that many of the hits on this ngram are for literal uses of the two phrases searched, but it shows that “on the same wavelength” first appeared around 1920 (not too long after Hertz’s work on wavelengths in the 1880s) and took-off around 1960.

Prior to that, “on the same track,” from its first appearance around the time of the first steam engine tramway locomotive in 1804 until it was surpassed by “wavelength” in/around 1970, was used more often than “on the same wavelength.”

Although probably not the best of references to cite, this thread from “WordReference/com” makes a connection between “… same wavelength,” “… same track,” and even “… same page,” seeming to conclude that all three mean: "understanding each other, communicating clearly."

Answer 3

I was thinking about "to be in sync" but was not very sure about its etymology. I explored a bit and found an idiomatic expression - in phase that redirected from "in sync"

According to the Free Dictionary

Also, in sync. In a correlated or synchronized way; in accord, in harmony.

For example,

If everyone were in phase we could step up the schedule

John and Pat often say the same thing at the same time; their minds are perfectly in sync .

Both versions of this idiom refer to physical phenomena. The first, dating from the second half of the 1800s, alludes to being at the same stage in a series of movements. The second, a slangy abbreviation of synchronization dating from the mid-1900s, alludes to exact coincidence in the time or rate of movement.

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Therefore, according to the timelines given, "in phase" could have been used much before "on the same wavelength". Ngram seems to validate this claim.