OP ARTS AND SCIENCES. 523 



laboratory his explanations were clear and patient, and be always 

 bore in mind the necessity of making the student think for himself. 

 His students, whether elementary or advanced, regarded him with a 

 warm affection, whicli was well merited by his exceeding kindliness, 

 and his devotion to their interests. 



In addition to these labors as a teacher he continued to serve as 

 Director of the Laboratory, and even published an eighth book, 

 " Laboratory Practice" (1891), a series of experiments to be used in 

 fitting students for Harvard College, and in the corresponding College 

 elective study, a course which he had founded, and in which he took 

 till the end the strongest interest. 



In 1892 he was elected President of our Academy, but in spite of 

 a journey to Alaska, which gave him much needed change and recrea- 

 tion, he did not survive long to enjoy this well deserved honor. In 

 the summer of 1894, after a most harassing winter, he went to his 

 country house in Newport, where he had passed the summers for 

 more than twenty years, and as soon as the strain of the term's work 

 was removed broke down almost completely. Nevertheless, he man- 

 aged to make out the European order for laboratory material for the 

 following year in the midst of pitiable weakness, and then slowly, but 

 without pause, faded away, until he died, on September 3, 1894. 



ADDKESS OF HENRY BAEKER HILL. 



The scientific work of Professor Cooke began soon after his ap- 

 pointment to the Erving Professorship, and continued throughout his 

 life. At first he seems to have been drawn toward subjects which 

 were more or less intimately connected with mineralogy, his favorite 

 pursuit, but in later years he turned to problems which tax to the 

 utmost the patience and ingenuity of the investigator, and devoted 

 the last half of his scientific life to the determination of atomic 

 weights. 



Forty one years ago, in December, 1853, he presented to the 

 Academy a preliminary sketch of an investigation into the numerical 

 relation of the atomic weights, and the Memoir uiDon this subject 

 which appeared a few months later is noteworthy in that it was one 

 of the early attempts to classify the elements through their atomic 

 weights. It is, however, to us especially interesting in that it con- 

 tained a discussion of the errors involved in the determination of 

 atomic weights, which in a way foreshadows the investigations which 

 occupied him in after life. The conclusions which he reached in this 



