Hamstead Birmingham | 25 Augt. 1860
My dear Sir,
I gave you the foci yesterday1 of the lower prisms of the two lights, as if there were only six prisms.
It was an inadvertence on my part.
There were eight lower prisms in each light.
The positions of the foci were:
Fixed light
20. 23. 26. 30. 34. 38. 43. 48 mm
and for the Revolving light
16. 19. 23. 26. 30. 34. 39. 44 mm
above the focal plane, the “stop” or “guage-tube” having been placed 18mm above the metallic burner for the fixed Light and 14mm for the Revolving one.
Yours very truly | J.T. Chance
Profr. Faraday | &c | London
Please cite as “Faraday3838,” in Ɛpsilon: The Michael Faraday Collection accessed on