vi PREFACE 



It was with difficulty, and only after a careful examination of many 

 hundred volumes of scientific journals and transactions, that the com- 

 mittee were able to obtain copies of all of Professor Eowland's numerous 

 and scattered articles; but they are convinced that no paper of import- 

 ance has escaped their notice. In preparing for publication these me- 

 moirs and addresses, no alterations other than typographical have been 

 made. 



For permission to reprint some of the most valuable papers, thanks 

 are due to various publishers. The committee wish especially to express 

 their appreciation of the kindness of Messrs. A. and C. Black, and of 

 The Times (London) for permission to reprint from the Encyclopaedia 

 Britannica the articles on " The Screw " and on " Diffraction Gratings," 

 and of the Engineering Magazine Company, of New York, for permis- 

 sion to reprint the article on " Modern Theories as to Electricity." 



The committee acknowledge their indebtedness also to Mr. 1ST. Mur- 

 ray, Librarian of The Johns Hopkins University, who has personally 

 superintended the details of publication, and whose advice has been 

 often needed. The proofs have been revised by Mr. E. P. Hyde, Fellow 

 in The Johns Hopkins University, who has thus been of the greatest 

 assistance to the committee. 



THE JOHNS HOPKINS UNIVERSITY, 



BALTIMORE, MARYLAND, 



DECEMBER 1, 1902. 



