74 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



o-eneral object, as finally summed up by Mr. Mtiller, is to de- 

 termine the absolute mean value of the magnetical declina- 

 tion on the 15th of October, 1872, upon the entire surface of 

 the globe, with instruments and according to the tests em- 

 ployed up to this time by the different observatories. The 

 magnetic stations which possess self-registering instruments 

 should take the mean variation of the twenty-four hours re- 

 duced to an absolute value. Those who do not possess such 

 instruments should determine directly the absolute magnetic 

 declination at eight o'clock in the morning, and two and six 

 in the afternoon. Directors of observatories are requested 

 to transmit the results of their observations to Mr. Midler at 

 Milan, with the assurance that they will be carefully collated, 

 and the comparative results published in a special report. 

 1 B.Nov. 5, 1871, 79. 



ACTION OF THE MAGNET ON ELECTEIC LIGHT. 



Professor Houston calls attention, in the journal of the 

 Franklin Institute, to the action of the magnet upon electric- 

 al light, first noticed by him in the course of an experiment 

 upon the rotation of light by the magnet. In this he ap- 

 proached a compound bar magnet to the light, holding it 

 with one end pointing directly to the arch, in a horizontal 

 plane, equidistant between the carbon electrodes. When the 

 nearest end of the magnet was four inches from the* elec- 

 trodes, the light was instantly extinguished. 



The cause of this phenomenon, he thinks, is to be attributed 

 to the tendency of the flame to rotate on the approach of the 

 magnet. This might cause the extinguishing of the light in 

 two ways : either by the irregularities on the surface of the 

 carbon electrodes offering greater resistance to the passage 

 of the current from some points than from others, or by the 

 current being unable to pass through the greater distance of 

 the arched path which is always assumed by the light on the 

 approach of a magnet. 



Another assumption, which is perhaps as probable as any, 

 is that on the approach of the magnet there is a slight in- 

 crease in the non-conducting power of the medium between 

 the electrodes, produced by their polarization, and which, 

 though always acting, can only manifest itself in a striking 

 manner when the distance between the electrodes is near a 



