AXJGUST 16, 1895.] 



SCIENCE. 



193 



praise. The pure geomagnetician will find 

 additional satisfaction in the fact that Pro- 

 fessor Hellmann appears to have abandoned 

 his original intention of publishing the 

 earliest meteorological and magnetic charts 

 in one and the same volume. This diifer- 

 entiation of purely meteorological and mag- 

 netic matter cannot be too highly com- 

 mended. 



As announced in the title, the purpose of 

 this number is to reproduce in facsimile the 

 earliest geomagnetic charts. The amount 

 of careful and painstaking research, as 

 evinced by the many copious notes follow- 

 ing the text, necessary for the completion of 

 this task can only be thoroughly appreciated 

 by those who have made similar attempts. 



Plate I, gives Halley's famous lines of 

 equal variation or magnetic declination for 

 the epoch 1700. 



Plate II, the earliest (1721) lines of equal 

 magnetic inclination by W. Whiston for 

 southern England and the Channel. 



Plate III, the earliest general chart of the 

 lines of equal inclination by J. C. Wilcke, 

 published in 1768. 



Plate IV, Humboldt's attempt at a repre- 

 sentation of the distribution of the intensity 

 of the earth's magnetism on both sides of 

 the equator passing through Peru,. 



Plate V, the earliest delineation of the 

 lines of equal magnetic force by Hansteen, 

 published in 1825 and 1826. 



A limited number of copies of the above 

 can be obtained from the reviewer at the 

 price named. L. A. Bauer. 



University of Chicago. 



SCIENTIFIC JOURNALS. 



THE PHYSICAL REVIEW, VOL. III., NO. 1, 



JULY-AUGUST. 



Thermal Conductivity of Copper. By R. W. 



Quick, C. D. Child and B. S. Lanphear. 



In a former paper (Phys. Rev., Vol. II., 

 No. 6) the writers have given an account 



of experiments made to determine the con- 

 ductivity of copper at temperatures ranging 

 from 70° to 170°. The present article is 

 devoted to experiments upon the same cop- 

 per bar at temperatures below 0°, the re- 

 sults being, so far as the writer is aware, 

 the first that have been obtained for this 

 range of temperatures. Several modifica- 

 tions in the method employed were made 

 necessary by the new conditions. As a 

 cooling bath, in which one end of the test 

 bar was immersed, a mixture of solid CO 2 

 and ether was used. The temperature ob- 

 tained by this means was about — 70°. The 

 formation of frost on the surface of the cold 

 bar was a source of some annoyance, but 

 was finally prevented by placing the bar in 

 a large box filled with dry air. The tem- 

 perature of the bar was measured, as in the 

 previous experiments, by the resistance of a 

 coil of fine copper wire, whose temperature 

 coefficient was determined by reference to 

 the melting points of ice and mercury. 



The results show a variation in conduc- 

 tivity from 0.921 at — 51° to 1.059 at 13°. 

 It is to be observed that the increase of 

 conductivity with rise of temperature cor- 

 responds with the behavior of the bar at 

 high temperatures. The increase is, how- 

 ever, more rap)id for temperatures below 0°. 

 On the other hand, the average value of the 

 conductivity for the range — 54° to — 13° 

 is found to be slightly greater than the 

 average value between 70° and 170°. Ei- 

 ther, therefore, the results have been af- 

 fected by some undiscovered source of er- 

 ror, or else the curve of conductivity must 

 possess a maximum at some temperature 

 between — 14° and -|-70°. Determinations 

 of conductivity for temperatures lying be- 

 tween this range are to be desired. 



On Ternary Mixtures. I. By W. D. Ban- 

 croft. 

 The attention which in recent years has 



been devoted to the subject of dissociation, 



