In reply to a request, made some years ago, for information regarding his collaboration with Prof. Stokes, Sir William Crookes promptly sent a privately printed correspondence extending from Mar. 1876 to April 1879, relating mainly to the radiometer and the viscosity of ramified gases, and also various packets of letters relating to other subjects. His permission to make use of these documents has been fully taken advantage of, only such letters and passages as were of merely temporary interest having been omitted. In spite of the disclaimer in the letter next following, the reader will fully appreciate the value and the joint results of this combination of Sir W. Crookes’ unrivalled experimental skill and bold intuition, with the refined theoretical insight of Sir George Stokes.

Oct. 16, 1904.

My Dear Larmor,

In '76 to '79 I was corresponding with Sir G. Stokes frequently, and as I had the greatest difficulty in making out his writing I sent the letters to my printing office and got the head printer there (who could decipher almost anything) to set them in type. Then after collation and correction so as to get them correct I had a few copies printed off. No one but myself has ever seen them in this form, but now I send them to you—the second man of science who sees them.

These are only a selection; many of minor importance came between. But they serve to show the enormous indebtedness I, in common with most scientific men who corresponded with him, owe to Stokes.