I am reading my copy of Davis and Foote about adjusting the transit.
There is a level tube on the telescope.
So if the plate levels are in adjustment and I level the telescope level it will stay level as I rotate the transit around the vertical axis.
So it dawned on me the telescope level needs to be parallel to the telescope.
I assume the way to check this is level it, sight a rod, invert the telescope, level it and sight the rod again and it should read the same.
Have I got that right?
I would peg it like a level.:-/
> So it dawned on me the telescope level needs to be parallel to the telescope.
>
> I assume the way to check this is level it, sight a rod, invert the telescope, level it and sight the rod again and it should read the same.
You adjust the telescope level as you would a wye level vial by the two peg method.
Then you adjust the vertical circle vernier if necessary so that it reads correctly when the telescope is level.
Do not follow any suggestions regarding the adjustment of the vertical on the plumb bob, however.
The telescope level needs to be perpendicular to the vertical axis.
(Get it to stay in one location as you turn it around the vertical axis. When you find that spot, adjust the bubble to be centered.)
The line of sight through the horizontal crosshair needs to be parallel with the telescope bubble and therefore perpendicular to the vertical axis.
> The telescope level needs to be perpendicular to the vertical axis.
> (Get it to stay in one location as you turn it around the vertical axis. When you find that spot, adjust the bubble to be centered.)
>
> The line of sight through the horizontal crosshair needs to be parallel with the telescope bubble and therefore perpendicular to the vertical axis.
Isn't the problem with that method that it depends entirely upon the vertical circle vernier being in good adjustment, i.e. that the telescope is perpendicular to the vertical axis when the circle is set to an altitude angle of 0-00-00?
Since the vernier can be out of whack, I'd think it's a better practice to adjust the telescope level by the two peg method and then check that the vernier reads 0-00-00 when the telescope is level.
> I am reading my copy of Davis and Foote about adjusting the transit.
By the way, probably the best accounts of adjusting transits and levels are in the earlier surveying texts. The 1940 3rd Edition of Davis & Foote gives on Page 301 as Steps 5 and 6 the same directions I mentioned earlier, i.e. adjust the telescope level by the peg test and then adjust the vernier to read zero.
The telescope bubble is the key feature and everything else is adjusted around it.
I agree that the vertical circle is adjusted last.
I have the third edition of Davis and Foote.
> The telescope bubble is the key feature and everything else is adjusted around it.
Not to be nit-picky, but isn't the horizontal collimation of the telescope the key feature? The cross-hairs are adjusted and then the line of sight through the horizontal hair is oriented horizontal by the two peg method. With the telescope in that orientation, the telescope vial is adjusted to indicate level, (and then, of course, the vernier reading is adjusted to zero).