Faraday to John Barlow   28 February 1855

Royal Institution: February 28, 1855.

My dear Barlow, - I return you Airy’s second note¹. I think he must be involved in some mystery about my views and papers; at all events, his notes mystify me. In the first, he splits the question into (a) action inversely as the square of the distance, and (b) metaphysics. What the first has to do with my consideration, I cannot make out. I do not deny the law of action referred to in all like cases; nor is there any difference as to the mathematical results (at least, if I understand Thomson² and Van Rees³), whether he takes the results according to my view or that of the French mathematicians. Why, then, talk about the inverse square of the distance? I had to warn my audience against the sound of this law and its supposed opposition on my Friday evening⁴, and Airy’s note shows that the warning was needful. I suppose all magneticians who admit differences in what is called magnetic saturation in different bodies, will also admit that there may be and are cases in which the law of the inverse square of the distance may not apply to magnetic action; but such cases are entirely out of the present consideration.

As to the metaphysical question, as it is called. If the admitted theory of gravitation will not permit us to suppose a new body brought into space, so that we may contemplate its effects, I think it must be but a poor theory; but I do not want a new body for my speculations, for, as I have said in the Friday evening paper, the motions of either planet or comet in an ellipse is sufficient base for the strict philosophical reasoning⁵; and if the theory will not permit us to ask a question about the conservation of force, then I think it must be very weak in its legs. The matter in the second note is quite in accordance with my views as far as it goes, only there is at the end of it a question which arises, and remains unanswered: When the attractive forces of the earth and moon in respect of each other diminish, what becomes of them, i.e. of the portions which disappear?⁶

Ever, my dear Barlow, yours truly, | M. Faraday.