130 ANNUAL OF SCIENTIFIC DISCOVERY. 



During a thunder storm, the atmospheric electricity attracted by the 

 wires passes over them to the chemically prepared paper, and thence 

 to the ground. As it passes from the wire to the paper, it emits a 

 bright spark, and produces a sound like the snapping of a pistol. At- 

 mospheric electricity never remains for any length of time on the 

 wires ; it will, however, sometimes travel many miles before discharg- 

 ing itself; I have seen discharges of electricity from the instrument, 

 which emanated from thunder storms forty or fifty miles distant. 



The effect produced by the Aurora Borealis on the wires, and the 

 record on the paper, is entirely different fro that of the atmospher- 

 ic current. Instead of discharging itself from the wires with a flash 

 and report, and without the aid of a conductor, as is the case with the 

 latter, it glides along the wires in a continuous stream, producing the 

 same result on paper as that produced by the galvanic battery. It is 

 well known that only the positive pole of the battery produces the 

 colored mark on the paper the negative having the contrary effect 

 of bleaching it ; the same is also true of the two currents from the 

 Aurora. The current usually commences lightly, producing a light 

 blue line just perceptible on the paper and gradually increases in 

 strength, making a dark blue, and then a black line till finally it 

 becomes so strong as to burn through several thicknesses of it ; it then 

 gradually disappears, and is followed by the bleaching process, which 

 entirely neutralizes the current from the batteries. 



In my diary of September 29, 1851, 1 find the following account of 

 the effects of the Aurora on the evening of that day : " All the lines 

 leading from the city are so strongly charged with atmospheric elec- 

 tricity this evening as to prevent operation. The surplus current on 

 the Chemical Line is equal to one hundred and fifty Grove's cups ; 

 and the same seems to be the case on the House and Morse wires. 

 The weather is cloudy, but through the clouds we can occasionally 

 see the brilliant scintillations of an Aurora Borealis." The next day 

 I ascertained that the Aurora, as seen from Providence, New Haven, 

 and other places, was very brilliant. February 19, 1852, I find the 

 following description of the effects of the Aurora of that date, in my 

 journal : " Toward evening a faint blue line appeared on the paper, 

 which gradually grew stronger and darker, until at last it burnecl it ; 

 then gradually grew fainter until it disappeared, when it appeared 

 again in a new form, bleaching instead of coloring the paper. This 

 singular phenomenon continued until we closed, at a late hour in the 

 evening. The Aurora was very brilliant in the evening." 



Mr. llowe, Superintendent of the Boston and Vermont Telegraph 

 Company, showed me specimens of paper taken from instruments 

 on that line, at 12 o'clock at night three hours after the batteries 

 were taken off which were covered with light and heavy blue lines 

 and bleachings. These were caused by the Aurora of the 19th of 

 February. 



Our troubles from the Aurora are not confined to the evenings 

 entirely, though they are more frequent then. On several occasions I 

 have predicted in the afternoon that we should have an Aurora in the 



