December 11, 1896.] 



SCIENCE. 



811 



period than to correlate both the Potomac and 

 the time-break with the Jurassic and assume 

 that the lower Cretaceous horizons of Europe 

 lack representation in our Atlantic series. 



In drawing attention to these matters of ap- 

 parent difficulty I have no intention to con- 

 trovert Prof. Marsh's view, but merely to 

 show how desirable it is that he set forth the 

 reasons therefor. G. K. Gilbert. 



Washington, D. C, December 5, 1896. 



LE CONTE'S elements OF GEOLOGY. 



To THE Editor of Science : In commenting 

 on Le Conte's ' Geology ' (Science, November 

 27th), Prof. C. W. Hall objects to ' the multi- 

 plicity of theories advanced and discussed.' 

 He says : "A text-book should be the expo- 

 nent of a doctrine. It should be constructed 

 on the definite and positive plan best adapted, 

 in the mind of the author, to expound his body 

 of principles. When several theories are pre- 

 sented and the student practically told to take 

 his choice, or when he is told that all are true, 

 the function of the text-book disappears." The 

 student who leans upon a text-book based only 

 on facts and well understood phenomena ' sub- 

 jects himself to the inspiration of positive 

 ideas, and, in his intellectual processes, ac- 

 quires that habit of decision so essential to prac- 

 tical success.' 



It is with diffidence that I venture to dissent 

 from Prof. Hall's opinion, because he is an ex- 

 perienced educator and I am not ; but it appears 

 to me that something is to be said in favor of 

 occasionally submitting to students alternative 

 opinions regarding an unsettled question. The 

 scientific text-book which presents only facts 

 and accepted principles, or gives only the 

 author's opinion on open questions, must tend 

 to leave the student with the impression that 

 scientific knowledge is complete. The state- 

 ment and discussion of rival hypotheses not 

 only exhibits the actual incompleteness of 

 knowledge, but illustrates the method of prog- 

 ress, and it appears to me quite as important 

 to the world's future that the rising generation 

 shall learn the method of research as that it be- 

 come acquainted with the results of research. 

 It may also be questioned whether the habit of 

 decision inspired by the exclusive assimilation 



of positive ideas will usually lead to the best 

 results when applied to the practical affairs of 

 life. Problems of affairs resemble, in the com- 

 plexity of their factors, the problems of such a 

 science as geology ; and the mind which habit- 

 ually suspends judgment until various points of 

 view have been considered may gain, through 

 the wisdom of its decisions, as much as it loses 

 through delay. G. K. Gilbert. 



Washington, November 30th. 



THE POSITION OF THE COMPANION OF SIRIUS. 



To THE Editor of Science: A brief statement 

 regarding the correspondence of the position of 

 the companion of Sirius as observed with the 36- 

 inch refractor of this observatory with the posi- 

 tions obtained from the published elements may 

 be of interest to the readers of Science. 



So far as I know, four sets of elements have 

 been published, which are based upon all the 

 micrometric measures previous to periastron, 

 namely, those by Auwers, Burnham, Howard 

 and Zwiers. Mr. Burnham gives no ephemeris 

 with his orbit (period, 51.97 yrs.), but from the 

 elements it is safe to say that his ephemeris 

 would not differ very widely from that com- 

 puted by Zwiers. An approximate interpola- 

 tion in the ephemerides by the other computers 

 gives the following position for 1896.8 : 



P. 



Howard (A. J. 235) 214.° 6 

 Auwers (A. N. 3085) 175. 7 

 Zwiers (A. N. 3336) 186. 4 



s. Period. 



4.^^75 (57.02 yrs.) 



3. 92 (49.40 " ) 



4. 05 (51.10 " ) 



The simple mean is 192. °2 4.^^24 



The mean of five measures of position angle 

 and four of distance by Prof. Schaeberle and 

 myself gives for the same date, 189. °3, 3.^^67 

 (A. J. 388). This communication is suggested 

 by the note on the same subject by ' H. J. ' in 

 the November 20, 1896, number of Science. 



K. G. AlTKEN. 



Mt. Hamilton, November 30, 1896. 



compliment or plagiarism. 

 My courteous friend. Prof. Fiske, hastens to 

 acknowledge that the quotation from Halsted's 

 Elementary Synthetic Geometry in Science, p. 

 656, shows that "the criticism is not applicable 

 to his more recent work. ' ' 



