abstracts: geology 301 



introduced by accidental bending of the index will be least if dM/d9 

 is constant over the whole range of moyement, M being the mutual 

 inductance of the coils and 9 the angle by which one is turned with 

 respect to the other. 



Features of design which affect the accuracy are briefly discussed. 

 These include permanent magnets, springs, and ratio of the torque of 

 the moving element to its weight. 



When a direct-current voltmeter is connected to two points on a 

 network, the reading is in general not a measure of the previous po- 

 tential difference of the points because the voltmeter takes a current 

 and thus alters conditions in the network. By taking a second reading 

 with the voltmeter shunted by a resistance equal to its own and using 

 a simple formula, this potential difference may be found. Similarly, 

 when a direct-current ammeter is inserted in one branch of a network, 

 the currents in the network are altered by the addition of the resist- 

 ance of the ammeter. By taking a second reading after adding extra 

 resistance equal to that of the ammeter, the same form of expression 

 will give the current in the branch before inserting the ammeter. 



The electrodynamic wattmeter is treated in considerable detail. 

 An equation by Laws is developed into a general correction formula for 

 the effect of both self and mutual inductance, from which the effect of 

 either can be found. 



The principal sources of error in electric energy meters and features 

 which should be improved in these and other electrical measuring in- 

 struments in the near future are briefly discussed. H. B. B. 



GEOLOGY. — Bibliography of the metals of the platinum group — osmium, 

 platinum, palladium, iridium, rhodium, ruthenium, 1 748-191 7. 

 Jas. Lew^s Howe and H. C. HolTz. U. S. Geol. Survey Bull. 

 694. Pp.555- 



The first edition of this bibliography, by Dr. Howe, was published 

 in 1897 as a volume of the Smithsonian Miscellaneous Collections and 

 gave a list of the articles on the metals of the platinum group found in 

 scientific literature to the end of 1896. A supplement to this edition, 

 prepared by Dr. H. C. Holtz, of Amsterdam, brought the record down 

 to 19 10 but was never published. Dr. Howe received the manuscript 

 of this supplement and has filled its gaps and brought the record down 

 to the end of 191 7. The 450 pages of bibliographic references are fol- 

 lowed by an author index and a subject index. R. W. Stone. 



