SOLAR UPHEAVAL AND MAGNETIC STORM. 51 S 



Sun that cast up matter with a rate of 120 miles per second. On writing to En- 

 gland he received reply that at the same time the British magnets were in agita- 

 tion. Many theories have been advanced in explanation. One quite ingenious 

 was announced by Barlow, who regarded the earth as a helix. He took a wood- 

 en globe and placed it on an axis inclined 2^j4° from a perpendicular, like the 

 axis of the Earth. He passed insulated wires around it in positions in relation 

 to latitude that isogonic and isoclinic lines are known to occupy on the real 

 Earth. Above the globe at different places he suspended horizontal and dipping 

 needles and then passed a strong electric current through the encircling; 

 wire. The needles behaved with remarkable similarity to those on the Earth, 

 dipping and changing declination very much as do actual magnetic needles. He 

 thought, therefore, that currents of electricity around the Earth induced terres- 

 trial magnetism. But how magnetic unrest on the Sun affects this earthly current: 

 is still unknown. Some think the Earth a vast thermopile, which, when one 

 side is heated by the Sun, produces changes in intensities of earth currents affect- 

 ing the strength of the magnetic induction in such a way that the needles are en- 

 abled to detect it. But no known fact in thermo-electricity substantiates this 

 idea. Again, the spectroscope, armed with a bolometer, reveals that sun-spots 

 emit less heat than the solar surface, rendering the theory untenable. The bond) 

 of union between auroras and oscillations of the Earth's magnetism is also unex- 

 plained. 



The whole series of experiments conducted during the last hundred years 

 may be summed up into three facts: i. The sun-spots have a periodic time of 

 about eleven years. If we have, say, this year a' maximum number of sun-spots,, 

 in eleven years another maximum will occur, requiring two years to reach the 

 greatest number and two years to decline, the remaining seven years of the eleven 

 presenting few periods of agitation on the Sun. 2. The number of auroras is the 

 greatest during the year of sun-spot maximum. 3. At the time of the greatest, 

 turbulence on the Sun the most rapid changes in electric force takes place on 

 Earth. 



The sun-spot of November 17th, the aurora, and the magnetic storm were 

 jtnong the most remarkable known. 



The present spot is so large that anybody can see it by simply viewing the 

 Sun with a smoked glass. 



The history of astronomy presents several such instances. In A. D. 807 a_ 

 large solar spot was seen by the inhabitants of Europe ; Kepler saw one in 1609 ; 

 and that of April 16, 1882, could also be seen without other optical aid than a 

 darkened glass. 



We timed the transit of the spot on November 19th, the time across central, 

 wires being 13 seconds. With a solar parallax on 8.8", the linear value of 

 I second of arc at the Sun's distance from the Earth is 450.309 miles. Since 

 I second of time of* the Earth's rotary motion is equal to 1 5 seconds of arc, 

 13 seconds is equal to 195 seconds arc in space, which, multiplied by 450.309 



