What is the instrument for measuring sunshine?

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Tags

1. #spherical
2. #recording
3. #campbell
4. #focus
5. #called
6. #specific
7. #performed
8. #duration
9. #purpose
10. #instruments
11. #specially
12. #glass
13. #recorders
14. #stokes
15. #sunshine
16. #which
17. #measurement
18. #designed