what are these devices?

[Jerome W. Young]

transformer or insulator of some kind. [small devices at this open junction]

[Jerry Peck]

Low voltage solenoids for operating lights.

Some low voltage systems located all of the solenoids grouped in a panel, other low voltage systems located the solenoids at the light junction boxes.

Power was run to the lights and solenoids, then low voltage wring was run to switches to control the lights via the solenoids.

[Gunnar Alquist]

Jerome,

You often hear a rather loud click from an indeterminate location when you operate the switch. The switches that I see are generally momentary contact rocker switches, but sometimes I will see switches that look like standard toggle style. Sometimes I will find a pair of rotary switches that will operate a dozen or so switches. These are often located in the master bedroom so a number of lights can be controlled from one central location.

[Jerry Peck]

Those systems were the precursor to today's Lite Touch systems.

I used to help my Dad install those systems, I remember one builder's house where we had something like 24 switches at the front entry door and the garage entry, so he could turn on or off any or every light in the house.

Today's Lite Touch systems you can program different buttons to turn different lights on/off, you can even press one 'All Off' button at any location(s) you want that at.