NATURAL PHILOSOPHY. Ill 



THE MOST ADVANTAGEOUS FORM OF MAGNETS. 



To ascertain this has been the object of a series of experiments by 

 Dr. Lamont, of Munich. Three determinations were required the 

 magnetic moment, the weight of the mass, and the moment of inertia. 

 For this purpose Dr. Lamont procured hardened steel bars of various 

 forms, magnetized them to saturation, and investigated every form by 

 measurement for the above-mentioned determinations. The results 

 are that narrow magnets are more advantageous than broad, thin 

 than thick ; and consequently the most advantageous form is that in 

 which breadth and thickness disappear and the magnet is transformed 

 into a mathematical line i. e., a so-called linear magnet an im- 

 aginary one. Practically, there are two forms which appear advanta- 

 geous the flat, contracting to a point from the middle, and the flat 

 prismatic. Details are given of six series of experiments, also tables 

 of results, and engravings of the various form of magnets employed. 



GALVANIC POLARIZATION OF BURIED METAL PLATES. 



In consequence of the disturbances observed in the telegraphic 

 wires during the appearance of the northern lights in 1859, Prof. La- 

 ment was induced to contrive an apparatus at the observatory of 

 Munich, in order to examine more, closely into the occasional motion 

 of the earth's electricity, and to determine its magnitude and direction. 

 For this purpose large zinc plates were buried on the north, south, 

 east and west sides of the observatory garden, the north plate being 

 connected with the south and the east with the west by means of 

 copper wires brought into the observatory and connected with gal- 

 vanometers. As Prof. Lamont, in testing the apparatus, remarked 

 certain phenomena which he attributed to galvanic polarization, it 

 appeared to Dr. Carl advisable to subject the matter to more careful 

 examination and to obtain more accurate measurements. Through 

 the wire that connected two of the above-mentioned zinc plates a cur- 

 rent, which he calls the terrestrial current, was perpetually circulat- 

 ing, the intensity of which was indicated by a fixed deviation of the 

 galvanometer. Dr. Carl supposed that if a galvanic element were 

 inserted in these conducting wires and again renewed, then, provided 

 it caused no modification in the conductor, the needle of the galvano- 

 meter would return to its former position ; but if, on the other hand, a 

 state of galvanic polarization had been produced in the zinc plates, 

 then the deviation of the needle of the galvanometer, after the re- 

 moval of the element, would be greater or less than that exhibited by 

 it originally, according as the direction of the galvanic current had 

 been opposite to, or the same as that of the terrestrial current. On 

 trial, the latter result exhibited itself so unmistakably that no further 

 doubt could be entertained of the occurrence of galvanic polarization. 



INTERESTING OBSERVATIONS ON ELECTRICAL PHENOMENA. 



At a recent meeting of the American Academy, Prof. Win. B. 

 Rogers contributed the following observations relative to certain 

 electrical phenomena. 



