62 Scientific Intelligence. 



resistance is progressively increased by the insertion of a column 

 of liquid, a point is reached where the discharge becomes con- 

 tinuous. Interposing in the circuit above described a column of 

 copper sulphate solution 112 mm. long and 3 mm. in diameter, 

 and magnetizing a needle by a discharge of 8 mm. tension, which 

 sufficed to magnetize it to its center, the author finds that now 

 the direction of polarity conforms to the law of Ampere, and is 

 the same at different depths. Stronger discharges, under tensions 

 of 10 or 12 mm., give the same magnetic moment. Weaker ones 

 magnetize the needle to a less depth. Since now the depth of 

 the magnetization is a function of the quantity of electricity dis- 

 charged, it is evident that two discharges in opposite directions, 

 of which the second is the stronger, should leave the needle in 

 the same condition as if it alone had acted. But if the second is 

 so feeble as not to magnetize the needle to the center, it will pro- 

 duce a shell of polarity opposite to that induced by the first dis- 

 charge. So that when the needle is acted on by hydrochloric 

 acid, the magnetism produced by the second discharge would be 

 found in the superficial layers, while that of the first would be 

 observed at a greater depth. This result experiment confirms. 

 A needle magnetized by an oscillatory discharge alternating in 

 direction and decreasing in intensity, the first of which magne- 

 tizes it to the axis, will be found to develop successively on 

 immersion in hydrochloric acid, the different polarities due to the 

 different discharges. The resulting polarity of a needle mag- 

 netized in this way is of course uncertain, depending upon the 

 direction and intensity of the discharge, and especially of the 

 latter portions which magnetize the superficial layers. — C. _K., 

 ci, 947, Nov., 1885. G. r. b. 



8. Astronomical Papers prepared for the use of the American 

 Ephemeris and Nautical Almanac. Vol. II, parts 3 and 4. Velo- 

 city of Light in Air and Refracting Media. Washington, 1885. — 

 Professor Newcomb obtains as the final result of his experiments 

 at Washington 299,86Uzb30 kilometers per second for the velocity 

 of light in vacuo. Professor Michelson's entirely independent 

 experiments at Cleveland give substantially the same result 

 (299,853±60). His former experiments at the Naval Academy, 

 after correction of two small errors which he now reports, give 

 299,91 OdbSO. All these experiments were made with the revolv- 

 ing mirror, but the arrangements of the two experimenters were 

 in other respects radically different. The first of these values of 

 the velocity of light with Nyren's value of the constant of aberra- 

 tion (20"*492) gives 149'60 for the distance of the sun in millions 

 of kilometers. On account of the recent announcement by Messrs. 

 Young and Forbes of a difference of about two per cent in the 

 velocities of red and blue light, especial attention was paid to this 

 point by both experimenters, without finding the least indication 

 of any difference. In Professor Newcomb's experiments, a dif- 

 ference of only one thousandth in these velocities would have pro- 

 duced a well-marked iridescence on the edges of the return image 



