38 De La Rive on the Aurora Borealis. 



and can adjust it so as to work with the greatest accuracy of 

 which it is susceptible. The method of doing this is clearly 

 explained in Messrs. Home and Thornth waiters paper of direc- 

 tions, and many of our readers will remember the information 

 furnished by Mr. Burder in the articles published in Recreative 

 Science on a portable equatorial. 



The student will gladly avail himself of this instrument (1) 

 to find stars, or other objects he wants to look at; (2) to dis- 

 cover the name of any star by determining its exact position, 

 and then ascertaining from an almanack or chart what body it 

 must have been to have occupied such a position at such a 

 time; (3) to obtain the time within a few seconds by watching" 

 the transit of any star convenient for such a purpose. It also 

 possesses a high educational value, affording to teachers the 

 means of giving their pupils an initiation into many processes 

 of practical astronomy that ought not to be neglected in any 

 civilized school. 



The construction of the star-finder displays considerable skill. 

 To render such an instrument generally useful, it was necessary to 

 make it handy, cheap, and not easily deranged, and in these 

 several particulars Messrs. Home and Thornthwaite have suc- 

 ceeded extremely well. The telescope, although small, is of 

 excellent quality, giving a good view of Jupiter's moons, and 

 clearly showing e Lyra as a double star, on a bright summer's 

 night. The movements are smooth and stead}^, the gradu- 

 ation accurate, and every part firm and strong. Thus the 

 student will find it an excellent aid to Ms fascinating pursuit. 



DE LA RIVE ON THE AURORA BOEEALTS * 



M. de la Bive conceives that two general facts relating to the 

 aurora are established : 1st, "the coincidence between the ap- 

 pearance of the Boreal and the Austral Auroras : 2nd, that 

 auroras are atmospheric phenomena which take place within 

 the limits of the atmosphere, but not beyond it." He seeks to 

 show that the positive electricity carried to high regions of the 

 atmosphere by vapours from tropical seas, and which the trade 

 winds accumulate near the polar regions, acts by induction on 

 the negative electricity with which the earth is charged. There 

 results, he says, "a condensation of contrary electricities in 

 those portions of the earth and the atmosphere which are 

 nearest each other, and in consequence a neutralization in the 



* Comptes Eendus, June 9, 1862, p. 1171. A similar account is given in the 

 Archives des Sciences (Geneye), No. 54, and accompanied with, a drawing of the 

 apparatus. 



