206 abstracts: terrestrial magnetism 



A list of 245 asteroids and 45 comets was observed. Many asteroids 

 were secured at more than one opposition. A good many were found 

 by means of photographic plates exposed for the purpose, and two were 

 discovered at the Observatory. For some time the asteroids discovered 

 by the Rev. J. H. Metcalf of Taunton, Mass., were observed systematic- 

 ally, for the purpose of securing sufficient data so that orbits could be 

 computed, and the asteroids found and identified at the following oppo- 

 sitions. In the list are 20 of these bodies. 



Considerable attention was given, also to the Watson asteroids. 

 In general, it was intended to make observations of the minor planets 

 only when measures had been lacking for some time. 



Many of the observations contained in this volume have been printed 

 in the Astronomical Journal and the Astronomische Nachrichten. Also, 

 a good many discussions of observations have appeared in the same 

 journals. 



There are three appendices to Volume VI which include : the Mass of 

 Titan from Observations of Hyperion; the Orbits of Phobos and Deimos; 

 the Orbit of Enceladus; a Determination of the Solar Parallax from 

 Observations of Eros; Orbits of Asteroids and Comets; Reports on the 

 Transit of Mercury of November 10, 1894; and a List of Publ'cations 

 issued by the United States Naval Observatory, 1845-1908. 



The introduction contains convenient summaries, so that the mate- 

 rial contained in the volume proper can be found easily. Asaph Hall. 



TERRESTRIAL MAGNETISM.— Two new types of magnetometers 

 made by the Department of Terrestrial Magnetism of the Carnegie 

 Institution of Washington. J. A. Fleming. Journal of Terres- 

 trial Magnetism and Atmospheric Electricity, 16: 1-12, pis. 1 and 

 II. 1911. 

 The instruments described are the result of the experience gained in 

 the land operations of the Department of Terrestrial Magnetism, which 

 has emphasized the great need of more portable and more compact 

 instrumental outfits than were heretofore in general use, without any 

 sacrifice in the degree of precision obtainable. The controlling condi- 

 tions in the designs and construction of the instruments described were : 

 (a) portability; (b) compactness; (c) simplicity; (d) minimum of loose 

 accessories; (e) readiness for immediate use; (f) the attainment of an 

 absolute observational accuracy equal to that of the best field instru- 

 ments now in use. 



The new instruments are of two types. The first is a theodolite mag- 



