A while back I posted that I bought some new toys including a T4 and fairly quickly made a tripod for it.
Well, recently I have gotten back to the T4 and thought I'd share some discoveries.
- My T4 was made in 1948 and was the 34th T4 ever made. Over the years of production (up to the early '80's) they made a total of 439. I wonder how many still exist and, more importantly, how many are usable?
- I've spent a fair amount of time tracing out the electrical on it and have that figured out as well as all the lights working. Even outdoors (and the same with the T3) it's easier to use lights rather than mirrors.
- The other day I was looking for someone to clean the reticles and was having some difficulty finding the right person. So I read the manual - imagine that! Lo and behold, there is a set of instructions (six simple steps) to get at the 2 reticles and clean them off. Did it myself and they came out very well.
- And yes, I said 2 reticles. There is the standard fixed reticle and a moveable reticle (called the impersonal reticle) that is apparently useful in some observations. Haven't gotten that far yet.
- The striding level is amazing! It is built so that there is an air chamber at one end so that you can tip it up or down and adjust the amount of air in the bubble. Never seen that before. And the sensitivity is incredible. As you get close to level you can't turn a foot screw in small enough increments to move the bubble as little as you'd like. And the same with adjusting the level itself. The adjusting screws have to turn so little to really move the bubble around.
This is an incredible instrument. More reports to follow.
Thanks Dave! Always nice to see someone with passion for one of these instruments!
stay with it dave. you'll have it singing in a week. sid had some commentary on the purpose of the 'impersonal eyepiece'. since the t4 was so difficult to pull on to a star, once the operator DID make a pointing, the impersonal slider permitted up to about four more measurements from the same position. it is shifting the crosshair, right?
That's the basic idea as I understand it. And it depends on what you are measuring - that is apparent direction of motion - since you can rotate the eyepiece 90° so that it can shift up and down or sideways. Old Mr. Wild was one smart cookie to make all this stuff work.
And for those that might be interested, here's what it looks like looking through a T4.
In regard to the chambered vial ...
Depending on air temperature, add or take away air in the bubble so that it is aproximately 20 par wide. That's the intended operational width of the bubble. It is not necessary to perfectly center the bubble, only make sure that one end is not buried. When observing, record both ends of the bubble, and based on your sensitivity calibration, then compute the systematic error for the position of the bubble. Calibrating a T-4 Striding Vial can make for a weekend-long task, depending on your technique.
I recommend you purchase (from a used book seller): "Spherical and Practical Astronomy as Applied to Geodesy" by Ivan I. Mueller, Frederic Ungar Publishing Co., New York, 615 pages, 1969.
Dave-
Looking forward to more.
My first post '4 screw' was a T16.
Then when the T1AE hit the field crew, what an excitement to watch the results when it would "not work" if only just set up and not leveled.
Cheers
Derek
