True enough, a study of photos will show that they do indeed sag but in other photos they will be almost straight with little sag no doubt due to the prevailing temperature. It can also be seen that in most photos the wires can't be seen on telegraph and power poles and that is how I normally handled them on the layout.
Now here though is a photo clearly showing the sag in the wires in February 1969.
Photo by R Merchant
And here is another photo of the same wires (on the left above and over the 48 class below) with very little sag in March 1981.
Photo from Train Hobby Country Stations of NSW Part 1
As an aside, last night we were looking at the above (and below) telegraph poles at Ardglen station on Ron Cunningham's Werris Creek layout and after counting the insulators (48) we couldn't decide if we (meaning myself) would do them with the stretchy thread or not. There would be quite a strain on the two end poles even with the smallest amount of stretch on each of the 48 wires and as such the end poles may need to be remade with brass rod (perhaps the second last pole at each end also).
Ardglen station on Werris Creek layout showing telegraph poles, pre-production Eureka 40 Class on HUB set
I had been wanting to try the look of the telegraph wires but due to the cost of the stretchy thread available in hobby shops I had only used some purchased rust coloured Berkshire Hobbies E Z Line thread for a small section of fencing, I wasn't that impressed with the rust colour as when stretched it took on a new copper wire look.
I also had a comment posted that discussed the colour of the wires, copper wires for instance being a whitish pale green and power lines being black due to the PVC coating. I feel that the black ink makes the wires go grey which in my mind is close enough to pale green not to matter. Regarding the black PVC coated power wires, I really can't remember if they were coated in 1965 or not but see below for further comment.
When I sourced the knitting in thread I decided to give it a go. Then came the decision regarding the sag and I felt that it would be very difficult to get 12 wires all with the exact same sag so I went for the taut look.
As can be read in my last post there does appear to be black knitting in thread available and certainly for power lines I might have a go at the sag as power poles don't carry many wires and if the wire is not stretched it will look thicker as power wires do. The advantage of this thread is that it will stretch a long way if you catch it when reaching into a scene so that alone is worth the effort. Incidentally, the E Z Line comes in white, black, green and rust so the green and rust colours may be available as well as white and black.
I think I will do some fences wires with the black to see if they look more like rusted wire than the rust coloured E Z Line. Of course white thread coloured with the black ink could look like new wire.
My layout is nothing more than an experiment in techniques and this is just another.
Because in the hobby we have to work with in the physical limits of the materials we have available to attempt to replicate the real world we have to rely heavily on impression and perception to fool the eye (and now the ear but that is another story).
There is a rule called the 80/20 rule and it goes like this, it will take the same amount of time/effort to achieve the last 20% of some target as it did to get to 80%. I like to think of myself as trying to achieve somewhere between 80-90% and this is both related to having a largish layout and not being so focussed that I am driven.
To me, my hobby is about pushing the boundaries of what can be achieved, sometimes it works, sometimes it doesn't. Does this particular effect work, I don't know at the moment but I think I will probably carry on with it.
Is this a justification for doing something 'wrong', perhaps, but it is all good fun.