Ok, new one to me. Inspecting a 8 unit flat roof 1920’s apartment. In the attic these wires keep getting in the way. They’re steel or copper, and wired up knob & tube style. Yet, a tic tracer shows nothing, and they are bare wire. They also just end at the wall.
I think I got it, but what’s your guess?
Possible antenna?
Nope.
Though I know someone who considered a dissertation on using trees as antennas for military purposes…
Lightning rod?
Looks like nail knobs to me ??
What are nail knobs? Are you talking about:
If so yes, it’s the exact same knobs & tubes.
Yes thats what im talking about
See also
Yes “thing” was wired with knobs and ceramic tubes… but without insulation, and in an odd pattern a few inches below the tar & gravel flat roof. The question is what was the purpose of that set of wires, and how do I determine if it’s still in working condition?
Oh sorry lol i didnt read the fist post throughly
Maybe an early intercom or bell system??
An intercom, telephone, buzzer or door buzzer would typically require two wires. These are single wires, spaced at least 2-3 feet apart.
Im at a loss… grounding wires but those would typically be insulated… maybe some type of Temperature Sensors ?
It’s a “fukwiththehomeinspectorinahundredyears” Can’t believe you’ve never seen one 
From what I understand doing some reading, some early K&T installations had the neutrals return by another route. This was later frowned upon because you need a complete wiring diagram to figure out what is what.
I’ve seen this a few times in the past and IMO they’re using the old knobs as a retrofitted grounding system.
Of course this practice wouldn’t fly today, but back in the day it was commonplace to ground to metalic plumbing pipes and route the EGCs the easiest and fastest way possible, which many times was through the attic.
Another possibility is that they were using them as cloths hangars on rainy days. 
They were used for drying some pot plants in mom & dad’s attic, back in the day.
Insulator.
Additional observations:
I can say 100% that knob & tube never used bare wires for neutral: that would be crazy unsafe as neutral in a split phase system can carry current. There were many generation of K&T, leading up to modern colored plastic wires. But all of them insulated neutral. And while neutral did use multi-wire branch circuit and even “carter” layout: the neutral: never would be done like this. Not a neutral. This building has perfectly functioning knob & tube, and the grounds are accounted for. That old knob & tube is bulletproof in my area: great stuff.
I will try to ask Charles E. Fisher of the NPS, author of:
50 PRESERVATION
BRIEFS
Lightning Protection
for Historic Structures
Charles E. Fisher
National Park Service
U.S. Department of the Interior
Technical Preservation Services
I have a feeling it’s something of a lighting protection system. It’s not however a lighting rod. The wire is #14, and not run how you’d run such a thing. It seems instead to be set up to collect stray currents under the roof or something.
Was it nonsense and hope at time it was installed, or an integral protection that even new roofs should have?
From the article
It was common practice to locate the conductor on the
outside since most systems were installed on existing
buildings. However, installations that ran down the
interior still were occurring. An 1847 article in the
Burlington Gazette refers to a church in Philadelphia that
recently was destroyed as a result of lightning: "It was
provided with a conductor, but it ran down from the
steeple inside the church!…. Such blundering ignorance
as that of setting a rod to conduct the lightning into the
house, we have seldom heard of.
Insulating what?
It kind of sucked back in Oregon when they legalized pot… I could no longer laugh with buyers about grow operations in the attic
I am leaning more to what Bryce mentioned. Older lightning protection wiring. Probably had a lightning rod on the roof and the wiring in the attic eventually led to a ground rod on the exterior. Just a WAG though…
