Letter to George F. Fitzgerald from A. Gray
Title
Letter to George F. Fitzgerald from A. Gray
Creator
Date
Identifier
GFF 9/38
Subject
Description
A handwritten letter from A. Gray to Professor George F. Fitzgerald, dated, 9th of February 189.
A. Gray thanks Fitzgerald for his thoughtful criticism of his book and agrees with many points. He explains that a planned discussion of Maxwell’s theory and mechanical models was accidentally omitted and will be added in future copies. He acknowledges that the Hertzian experiments provide useful analogies but don’t fully explain the motions themselves. Gray hopes to expand on these ideas further in future publications and invites any papers or references Fitzgerald can share.
2pp.
Transcription:
Dear Fitzgerald,
I thank you very much for your letter of the criticism with which on the whole I am disposed to agree. I had planned to give some further discussion and illustrations of Maxwell's theory of the medium, among them his own mechanical illustration and your model. But that part of the book through promised ar p. 177 was accidentally omitted. It ought to have been given as an introduction to Chap. V; and you will see that this would have given the emphasis to the action in the medium just where it is most needed. I think of having a note printed and bound up with future copies of Part I which will help to remove this particular reproach.
"With regard to the direction of vibration of the ether" I mean precisely what you say. But no doubt the statement is not so full or so explicit as it ought to be. I hope however it still will tend to remove misunderstanding. As to yours statement that everything is.
Bare about the direction of vibration is known experimentally. Sup to the question of "what changes in the medium accompanies electric and magnetic displacement?" I can't agree with it. What I referred to was the "direction of vibration of the ether." I can't think of anything going in which either it is experienced as electric force or magnetic induction which is not a result or manifestation of motion of a medium possessing inertia. The elastic jelly theory of the ether illustrates what I mean, though only imperfectly, as its rigidity requires explanation. When applied to explain the scattering of light by small particles, as in lord Rayleigh's theory of the blue sky, this theory does so satisfactorily if the direction of vibration of the jelly be at right angles to the plane of polarisation in a plane polarised beam.
Now whatever theory of the constitution and mechanism of the ether is adopted (and anything hitherto thought of probably only dimly shadows the reality) I take it that the electric and magnetic force or "displacements" correspond to motions of the ether, and these motions must be vibratory motions. To the nature of these motions the Hertzian experiments give a clue by making known to us their analogue, but they do not settle the questions at all as to what these motions are themselves.
The knowledge of these analogies & their relation to the plane of polarisation is a great step in advance of I wish I had devoted another paragraph or two to the matter. Part I was merely put in to avoid words of Space, and help some friends experiment to admire me of observation and perfection. I had not at all in mind the Theory of Light and I succeeded in making a better job of it I mean
publish it separately in some form or other. In that case I hope to do justice to J. I need hardly say that I shall be very glad of any papers or references on this subject you can give me.
Yours very truly,
A. Gray
A. Gray thanks Fitzgerald for his thoughtful criticism of his book and agrees with many points. He explains that a planned discussion of Maxwell’s theory and mechanical models was accidentally omitted and will be added in future copies. He acknowledges that the Hertzian experiments provide useful analogies but don’t fully explain the motions themselves. Gray hopes to expand on these ideas further in future publications and invites any papers or references Fitzgerald can share.
2pp.
Transcription:
Dear Fitzgerald,
I thank you very much for your letter of the criticism with which on the whole I am disposed to agree. I had planned to give some further discussion and illustrations of Maxwell's theory of the medium, among them his own mechanical illustration and your model. But that part of the book through promised ar p. 177 was accidentally omitted. It ought to have been given as an introduction to Chap. V; and you will see that this would have given the emphasis to the action in the medium just where it is most needed. I think of having a note printed and bound up with future copies of Part I which will help to remove this particular reproach.
"With regard to the direction of vibration of the ether" I mean precisely what you say. But no doubt the statement is not so full or so explicit as it ought to be. I hope however it still will tend to remove misunderstanding. As to yours statement that everything is.
Bare about the direction of vibration is known experimentally. Sup to the question of "what changes in the medium accompanies electric and magnetic displacement?" I can't agree with it. What I referred to was the "direction of vibration of the ether." I can't think of anything going in which either it is experienced as electric force or magnetic induction which is not a result or manifestation of motion of a medium possessing inertia. The elastic jelly theory of the ether illustrates what I mean, though only imperfectly, as its rigidity requires explanation. When applied to explain the scattering of light by small particles, as in lord Rayleigh's theory of the blue sky, this theory does so satisfactorily if the direction of vibration of the jelly be at right angles to the plane of polarisation in a plane polarised beam.
Now whatever theory of the constitution and mechanism of the ether is adopted (and anything hitherto thought of probably only dimly shadows the reality) I take it that the electric and magnetic force or "displacements" correspond to motions of the ether, and these motions must be vibratory motions. To the nature of these motions the Hertzian experiments give a clue by making known to us their analogue, but they do not settle the questions at all as to what these motions are themselves.
The knowledge of these analogies & their relation to the plane of polarisation is a great step in advance of I wish I had devoted another paragraph or two to the matter. Part I was merely put in to avoid words of Space, and help some friends experiment to admire me of observation and perfection. I had not at all in mind the Theory of Light and I succeeded in making a better job of it I mean
publish it separately in some form or other. In that case I hope to do justice to J. I need hardly say that I shall be very glad of any papers or references on this subject you can give me.
Yours very truly,
A. Gray
Source
RDS Library & Archives GFF collection of letters
Contributor
Rights
Copyright RDS Library & Archives. Publication, transmission or display is prohibited without formal written approval of the RDS Library & Archives.
Relation
RDS Science Archive
Format
Manuscript
Language
English
Type
Coverage
1870-1901
Collection
Citation
Gray, A., “Letter to George F. Fitzgerald from A. Gray,” RDS Digital Archive, accessed December 5, 2025, https://digitalarchive.rds.ie/items/show/2352.