Intelligence and Miscellaneous Articles, 159 



Remarking that ^(x) preserves the constant value ^>(X) in the in- 

 terval from I to A, and also taking account of the equation which 

 determines the position of the pole, we find, lastly, 



J ^(^r=^(\)(Z-X). 

 o 



The increase of vis viva produced in the bar by the effect of the 

 magnetizing is therefore proportional to the square of the intensity 

 of the magnetism and to the polar distance. The effect of demag- 

 netizing corresponds to an equal loss of vis viva — which is the 

 measure of the thermal effect produced, if that effect is the only 

 one which accompanies the demagnetization. — Comptes Mendus de 

 V Ac-ad, des Sciences, vol. lxxv. pp. 1619-1621. 



Appendix II. of the ' Washington Observations ' for 1870 con- 

 tains a very interesting report by Professors Hall and Hark- 

 ness on observations of Encke's comet during its return in 1871. 

 The report of Professor Hall is confined almost exclusively to the 

 micrometrical observations for position made with the filar micro- 

 meter of the 9^-inch equatorial of the JSTaval Observatory. In the 

 closing portion Professor Hall describes the appearances of the 

 comet from the evening it was found, October 11, to December 7. 

 The report is accompanied by four exquisite engravings, represent- 

 ing the comet as seen on October 17, November 17, December 1, 

 and December 2. A note is added on the general fact of a con- 

 densation of the matter of the comet and formation of a nucleus 

 as it approaches to, and an expansion of the matter and a disap- 

 pearance of the nucleus as it recedes from, the sun. 



Professor Harkness enters elaborately into the spectroscopic ob- 

 servations of the comet, and describes the instruments employed. 

 The spectrum consisted of three bright bands of the following 

 wave-lengths : 549*5, 510*6, and 455. By a process of interpola- 

 tion, Professor Harkness finds that the wave-lengths of comet II. 

 1868, observed by Dr. Huggins, are so nearly identical with the 

 above as to lead to the conclusion that the physical constitutions of 

 the two comets are identical, and that both are composed of incan- 

 descent carbon in a gaseous state. 



The investigation of the density of the supposed resisting'medium 

 in space is exceedingly interesting. Professor Harkness deduces 

 the density in terms of the height in inches of the column of mer- 

 cury which it will support, and finds that it is somewhere between 



220 285 



-— and j^of an inch, which is " enormously greater than that of 



the atmosphere at the upper limit of auroras." Hence the proba- 

 bility that auroras are propagated in a medium which pervades all 



