his acute perception is his criterion for rejecting discordant observations. 

 Here, too, he found the mind was liable to be influenced by an unconscious 

 preference, and so made his selection from the several observations by a new 

 application of the mathematical law of probability. . . . 



In 1852 were printed Peirce's lunar tables, to be used in making computa- 

 tions for the Nautical Almanac, with which publication Professor Peirce was 

 long connected as consulting astronomer. Though intended to serve only a 

 temporary purpose, till the long-expected tables of Hansen should make 

 their appearance, these tables have ever since been retained in use as giving 

 results quite as accurate as are obtained by the aid of Hansen's computa- 

 tions. From 1852 to 1856 Professor Peirce made a laborious investigation 

 into the nature of Saturn's rings, and demonstrated that they are not solid, 

 but fluid, sustained by the planet's satellites. In j^jfappeared " A System 

 of Analytic Mechanics," consolidating "the latest researches of the great 

 geometers and their most exalted forms of thought," but containing brilliant 

 results of the author's own labor. From 1867 to 1874 he was superintendent 

 of the United-States Coast Survey; and in 1870, with the help of his asso- 

 ciates, there was published an edition of one hundred copies of certain papers 

 communicated to the National Academy upon "Linear Associative Algebra." 

 This work is an examination and enlargement of the new mathematical 

 science of quaternions. This science, in which distances and directions are 

 measured, not, as in ordinary algebra, by quantity, but by units of quality as 

 well, was developed by Hamilton in 1852, and is considered a most remarkable 

 achievement. Professor Peirce first explains the nature of qualitative and 

 quantitative algebras, and then shows that there may be a score or more of 

 algebras of distinct qualitative units. Among the important original re- 

 sults of his labor is a determination of the forms of equilibrium for a fluid 

 ir. an extensible sack in another fluid, and a theory of comets' tails. For the 

 past ten years of his life he published less. He withdrew more and more 

 from active work in the College, leaving his son, Professor James Mills 

 Peirce, to take his place in the class-room, while he gave himself up to the 

 enjoyment of the philosophic and religious beliefs which hi* lifelong pursuit 

 of science had unfolded and made dear to him. . . . 



At the time of the publication of his " System of Analytic Mechanics," 

 Professor Peirce announced that the volume would be followed by three 

 others, entitled respectively, "Celestial Mechanics," " Potential Physics," and 

 "Analytic Morphology." In them would have been expected some reference 

 to theology, but they were never published. In his recent lectures on " Ideal- 



