506 ELECTRICITY. 



The appearance of this spark is somewhat peculiar. 

 It is usually of bright yellow at the extremities, and blu- 

 ish in the middle. In discharging a Leyden jar, it is 

 short and intense in brightness ; when taken from a 

 prime conductor, it is much longer and fainter. The 

 length of the spark which can be drawn from a conduc- 

 tor depends upon the size of the machine, and the condi- 

 tion which it is in at the time of the experiment. Sparks 

 can without much difficulty be obtained several inches in 

 length. 



If, in receiving the spark from the conductor, the 

 operator, instead of presenting a small body like a brass 

 ball, presents a large fat surface, like the back of the 

 band, and if this surface is held at a considerable dis- 

 tance, the spark at a little distance from the prime con- 

 ductor will branch off into many beautiful ramifications, 

 presenting in the night, and under favorable circum- 

 stances, a splendid tree of fire. The size and beauty of 

 this tree will depend of course very much upon the ex- 

 cellence of the machine, and the circumstances under 

 which the experiment is made. 



This tendency of the electric fluid to give light when- 

 ever it passes through the air, produces many other re- 

 markable appearances, in working the machine in the 

 dark. Long sparks dart from the prime conductor to 

 the rubber. Bright lines and spots of light, ornament 

 the under surface of the rubber, and flashes and 

 trees of flame dart from side to side. These beautiful 

 appearances can only however be seen when the cir- 

 cumstances are highly favorable. 



There are many cases of common occurrence in 

 which this electric light appears. It is common for 

 children to amuse tUSms'elv^by rubbing the back of a 

 cat in the dark, to oJBtervProe sparks thus produced. 

 These are electrical, the fur of the cat being a most 

 excellent electric. A silk or flannel garment, will often 

 when taken off sparkle, and many a child, has, in a 

 cold winter night, been frightened at seeing sparks in 

 his bed, as he opens the blankets. The Aurora Borea- 

 lis is generally supposed, though without much direct 

 proof, to be an electrical effect. 



