Intelligence and Miscellaneous Articles. 73 



netism N S is capable of inducing, the magnet will not be able to 

 sustain any more, and consequently a limit to its inducing power 

 must exist. The reaction of the armature upon the magnet will 

 also strengthen the adhesion between them : probably the effect of 

 this reaction will be influenced by the facility with which magnetism 

 permeates the steel of which the magnet is made, and be greater 

 in the softer kinds of steel. 



If this view be correct, the sustaining power of a common mag- 

 net cannot be considered as an exact measure of its magnetic in- 

 tensity. 



When a piece of soft iron is placed at a short distance from the 

 poles of an electro-magnet, under the influence of a galvanic cur- 

 rent, a comparatively trivial effect is produced, showing that the 

 magnet thus induced is but of feeble magnetic intensity. This is 

 owing, probably, to the facility with which soft iron is permeated 

 by magnetism, and consequently any considerable accumulation 

 prevented. But when the iron is in contact with the poles of the 

 electro-magnet, the magnetism, instead of escaping, will induce in 

 the armature polarity, and the armature reacting powerfully on the 

 soft iron of the electro-magnet, and receiving continuous additions 

 of magnetism from the galvanic current, will be attracted by the 

 magnet with increasing force until the attraction between them be- 

 comes immense. If the galvanic action be discontinued, the keeper 

 will remain applied to the electro-magnet, though less firmly; and 

 after it has been removed nearly all the magnetism escapes. 



If this explanation be correct, it will be obvious that the electro- 

 magnet will not be well adapted for the construction of magneto- 

 electrical machines, in which the armature is made to rotate rapidly 

 in front of the poles of the magnet without actual contact. 



I am, &c. 



No. l,Maze Pond, Borough, May 7, 1836. George Rainey. 



OBSERVATIONS ON THE SOLAR ECLIPSE OF MAY 15, 1836; AND 

 ON THE AURORA BOREALIS OF APRIL 22. 



To the Editors of the Philosophical Magazine and Journal of Science. 



Gentlemen, 

 I am well aware that you must have received various accounts 

 of observations made during the late eclipse: nevertheless, I beg to 

 trouble you with one or two made by myself at that time upon the 

 possibility of seeing the lunar mountains on the round or unbroken 

 side of the moon, although it may be presumed that an account of 

 the singular appearance at the time of the annular phase has been 

 transmitted to you. I saw the roughness of the moon's edge from 

 the beginning of the eclipse ; but at the time of the ring becoming 

 nearly equal on the eastern and western sides its narrowest part was 

 divided directly across in two places, the light of the sun passing 

 between the mountains. This affords an excellent method of cal- 

 culating the heights of the lunar mountains ; for it may be readily 



