194 



SCIENCE. 



[N. S. Vol. II. No. 33. 



and to the development of the analogy be- 

 tween a dissolved substance and a gas, has 

 heretofore prevented a systematic consider- 

 ation of the more complex cases in which 

 the solubility of one substance is influenced 

 by the presence of a second. In the paper 

 before us, which is the first of a series of ar- 

 ticles on Ternary Mixtures, the exiDCri- 

 mental investigation of one of the simplest 

 of such cases is begun: viz., the case of 

 three liquids, two of which are non-misci- 

 ble, while the third is miscible with each of 

 the others in all proportions. Experiments 

 were made with chloroform and water, and 

 benzol and water, as non-miscible liquids, 

 while ethylalcohol, methylalcohol and ace- 

 tone were used as solvents. The quantity 

 of solvent being kept constant, the amounts 

 of the other two components necessary to 

 produce saturation were determined. The 

 results are found to be closely in agreement 

 with the ' mass law ': i. e., if x and y de- 

 note the amounts of the non-miscible liquids 

 the condition for saturation is .t " 2/ '^ = t' 

 where «, ;5, and C are constants. When 

 the curve showing the relation between x 

 and y is plotted it is in general found, how- 

 ever, that a single curve is not sufficient to 

 represent the experimental results. There 

 appear to be two sets of conditions leading 

 to equilibrium. A mixture of chloroform, 

 water and alcohol may, for example, be 

 saturated with respect to chloroform; in 

 which case a precipitate of the latter liquid 

 will be formed on the addition of either 

 chloroform or water. A mixture of the 

 same liquids may also be made which is 

 saturated with respect to water. The pro- 

 portions of water and chloroform are, of 

 course, difl'erent in the two cases. The pa- 

 per contains a discussion of several such 

 cases, as Avell as numerous tables of experi- 

 mental data. 



On the Secular Motion of a Free Magnetic 

 Needle. II. By L. A. Bauer. 



The accumulation and discussion of the 

 observational data used by Dr. Bauer have 

 been described in the first half of this paper 

 (Phys. Bev., Vol. II., No. 6), and have al- 

 ready been noticed in Science. Practically 

 all available sources of such data have been 

 thoroughly searched, and the results col- 

 lected constitiite in themselves a valuable 

 contribution to the literature of geomagnet- 

 ism. Bjr a combination and comparison of 

 these data the author derives in the present 

 paper certain important general laws re- 

 garding secular magnetic changes, which 

 can perhaps best be stated in the language 

 of the paper : 



1. "In consequence of the secular variation o£ geor 

 magnetism, the north end of a freely suspended mag- 

 netic needle, viewed from the center of suspension of 

 the needle, moves on the whole earth in the direction 

 of the hands of a watch." 



2. " The secular variation curves appear to develop 

 themselves more and more as we go around the earth 

 eastwardly; or, in other words, the secular wave ap- 

 pears to travel in the main, roughly speaking, west- 

 ward. ' ' 



3. "The north end of a free magnetic needle, 

 viewed from the center of suspension of the needle, 

 moves clockwise in making an instantaneous easterly 

 circuit of the earth along a parallel of latitude." 



4. "The secular variation and the prevailing dis- 

 tribution of geomagnetism appear to he closely re- 

 lated." 



Plates showing secular curves at different 

 stations, as well as ' instantaneous curves ' 

 for several latitudes, accompany the paper. 

 The author promises a mathematical dis- 

 cussion of the subject in the near future. 

 Apart from the interest and value of the re- 

 sults obtained by Dr. Bauer, the directness 

 and thoroughly scientific character of the 

 work done form a pleasant contrast to the 

 speculative and superficial methods by 

 which the complex problem of geomagnet- 

 ism are so often attacked. 



A Galvanometer for Photographing Alternating 

 Current Curves. By H. J. Hotchkiss and 

 F. E. MiLLis. 

 For the investigation of many important 



