524 Scientific Intelligence. 



9. Registration of Magnetic variations. — Eschenhagen, at 

 the magnetic observatory of Potsdam, employs a length of 

 abscissae equal to 20 mm per hour and obtains a fine curve by dia- 

 phragming the lens, determining exactly its chemical focus and 

 by employing a very small mirror. The slit employed is 0'25 mm . 

 The magnetic mirror is made in three parts or facets inclined to 

 each other at an angle of 3°. It is enclosed in a bell jar in which 

 the air is kept dry and free from sulphur vapor. The mirror 

 gives three beams. During a strong disturbance just before the 

 beam from the middle mirror leaves the drum, another point 

 appears on the opposite side, which continues the record. — Met. 

 Zeitschr.; Nature, April 6, 1893. j. t. 



10. Discussion of the Precision of Measurements toith examples 

 taken mainly from Physics and Electrical Engineering; by Silas 

 W. Holman. 176 pp. 8vo. New York, 1892. (John Wiley & 

 Sons). — Professor Holman's work is of somewhat novel character, 

 and will be of much service to students and workers in experi- 

 mental physics, pure and applied. It discusses with thorough- 

 ness, and with numerous practical examples, the general subject of 

 precision of measurements, first, direct, and second, indh'ect 

 measurements. The author's wide experience has enabled him to 

 select wisely the special kinds of measurements discussed, and it 

 would be difficult to find in so convenient a form elsewhere the 

 variety of material here brought together. 



11. Practical Physics: An Introductory Handbook for the 

 Physical Laboratory ; by W. F. Barrett and W. Brown. 

 Part I, Physical Processes and Measurements, the Properties of 

 Matter. 284 pp. 12mo. London, 1892. (Percival & Co.). — This 

 little volume presents in simple form, and with numerous ex- 

 amples worked out numerically, the introductory part of prac- 

 tical physics as needed Jby rather elementary students. 



II. Geology and Natural History. 



1. A new Geological Society. — A Geological Society has re- 

 cently been organized in Washington, D. C, for the presentation 

 and discussion of topics of interest to geologists. The Constitu- 

 tion and standing rules were subscribed to by 109 founders at the 

 first public meeting, March 8th, 1893. Its members are of two 

 classes, active and corresponding. The annual dues of the first 

 are $2, and of the second, $1. Meetings will be held on the sec- 

 ond and generally also on the fourth Wednesday of each month 

 from October to May, inclusive. 



The journals and bulletins of the various societies appear to 

 furnish sufficient opportunity for the publication of papers read 

 before the Society, so that for the present the Society will not 

 undertake to publish the papers presented. It will probably issue 

 one bulletin each year containing the address of the retiring 

 President and such other matter as the Council directs. All 



