Faraday to George Biddell Airy   26 April 1854

Royal Institution | 26 April 1854

My dear Sir

The impression produced on my <<m>>ind by your reports¹ is first that observers have not yet learned what is requisite for a safe or a constant observation on their own part and next what circumstances about any given locality may affect the result. I do not know how far your observers have compared themselves with themselves or with others but without some proof of certainty in the results at one place it would be hardly worth while comparing them in different places. The following questions will illustrate my meaning[.]

Does an observer making three of four simultaneous observations in the same place obtain a like result by all?- if there is a difference what is the extent?

Does another observer obtain the like accordance or discordance with himself in the same place?- What is the state of accordance between him & the former observer?

Do observations made on two or four sides of the observatory by the same person agree together?- if not is the difference constant?

Do those made by two observers or more simultaneously in these different places agree for the same place & time?

If the results are satisfactory & the power of observing seems to be obtained then observations at places further apart would be required. I imagine a great difference is to be expected between a clear open space and the neighbourhood of a building and I conceive that no general results can be expected to agree well before the influence of all minor circumstances has been ascertained - the corrections in fact worked out[.]

Ever My dear Sir | Truly Yours | M. Faraday

G.B. Airy Esq | &c &c &c