Twelve inch cylindrical metal rod
- Made:
- 1948-1961
Twelve inch cylindrical metal rod, 'Merton's Helix', used to make primary and secondary rulings of 7500 lines/ inch, enclosed in perspex tube, 1948-1961.
Twelve inch cylindrical metal rod, 'Merton's Helix', used to make primary and secondary rulings of 7500 lines/ inch, enclosed in perspex tube, 1948-1961.