242 LEADING AMERICAN MEN OF SCIENCE 



sympathize with each other. Professor Dana was compelled to 

 drop his college work, for longer or shorter periods, in 1869, 

 1874, and 1880, and in 1890 he finally relinquished the work of 

 teaching. All through the last four decades of his life he worked 

 under the oppressive limitations of nervous exhaustion. He con- 

 scientiously avoided all social excitements, very rarely attending 

 even the meetings of scientific associations. By thorough self- 

 control, by careful regimen as regards sleep and exercise, by the 

 conscientious economizing of the short working periods which his 

 weary head could bear, and by the watchful care of his wife, he 

 was enabled to keep up his intellectual activity and productiveness 

 beyond the age of four-score. 



In 1862 was published the book which has probably had, on the 

 whole, a larger influence on the general intellectual life of the 

 world than any other of Dana's writings the Manual of Geol- 

 ogy. Later editions of this work were published in 1871, 1880, 

 and 1895. The fourth edition was the last important labor of his 

 life, appearing only a few weeks before his death. In 1864, Dana 

 published a smaller book entitled, Text-book of Geology, of which 

 several later editions have been published, and which has been 

 very widely used in the colleges and high schools of this country. 



In 1872 was published Corals and Coral Islands an elegantly 

 illustrated book, in which were presented in semi-popular form 

 some of the results of Dana's work in the Exploring Expedition. 

 A second edition of this work was published in 1890. 



In the summer of 1887, Dana visited again the Hawaiian vol- 

 canoes, which he had first studied almost a half-century before. 

 Great changes in means of communication and in the condition of 

 the Hawaiian Islands had taken place since 1840, and the journey 

 was a far easier one than at the earlier date. It was nevertheless 

 somewhat of an adventure for a man seventy-four years of age. 



In 1890 was published Characteristics of Volcanoes. In this 

 work the Hawaiian volcanoes are very fully described, and the 

 general theory of vulcanism is discussed. In addition to the studies 

 of the Hawaiian Islands in 1840 and in 1887, Dana had seen in 

 his circumnavigation of the globe and in his European tours a 



