556 JAMES CLERK MAXWELL. 



passage or allusion was the subject of a long and searching 

 investigation; and many were the letters written to the 

 Librarian of the Eoyal Society and to scientific and literary 

 friends in different parts of the country, to gain information 

 respecting the meaning of obsolete words and symbols, or 

 the history of individuals. But besides this, and a comparison 

 of Cavendish's results with those obtained by subsequent 

 investigators, Maxwell repeated many of Cavendish's experi- 

 ments almost in their original form, only employing modern 

 instruments for the purposes of measurement. The intro- 

 duction and the appendices to the work evidence much 

 labour, patient investigation, and very extensive acquaintance 

 with the literature bearing on the subject. Maxwell was by 

 no means one of the class of " thinkers " who only read their 

 own writings ; his acquaintance not only with scientific 

 literature, but with nearly every other class of books was 

 astonishing ; and if any question of physics was brought 

 before him, he could generally give an account of nearly 

 all that had been done in the subject. In this respect 

 he resembled the late Professor W. H. Miller, whom Cam- 

 bridge men used to consult about everything. 



It would be impossible here to give any adequate account 

 of Maxwell's work in connection with the Cavendish papers, 

 but we may mention one experiment both on account of its 

 intrinsic importance and of the interest which Maxwell took 

 in it. Cavendish describes an experiment (see p. 104 of 

 The Electrical Researches) in which a sphere of 12'1 inches in 

 diameter was enclosed between two copper hemispheres 13 '3 

 inches in diameter, and the copper hemispheres, which were 

 supported in frames hinged together, and opened or closed by 

 silk cords, were brought together so as to enclose the sphere, 

 contact being made at the same time between it and the 

 hemispheres. The outer sphere was then charged, and the 

 connection between it and the inner sphere removed. On 

 separating the hemispheres, the inner sphere was found to be 

 discharged, or at least the charge, if any, left upon it was too 

 small to affect Cavendish's pith ball electrometer. Knowing 

 what fraction of the original charge could not fail to be de- 



