98 Mr. J. P. Gassiot on Experiments made with RuhmkorflF's Coil. 



2. Through the flame of a spirit-lamp the discharge passes at 

 a separation of 1 to 2 inches; and if the inner and outer 

 coatings of a moderate-sized Leyden jar are attached to the ter- 

 minals of the coil by other wires, this discharge is mucli height- 

 ened in its intensitjr, a long, clear and brilliant white electrical 

 stream passing through the flame with a sharp rattling noise. 



3. If the terminals are of platinum wire, and the ends are 

 approximated to within O'l of an inch, a rapid continued dis- 

 charge takes place, and in a short time the negative wire becomes 

 red-hot ; the current being reversed, this wire instantly cools, 

 and the heat appears in the other, which has now become the 

 negative. 



This heating effect of the secondary current has already been 

 noticed by Masson, but the heat appears in the contrary direc- 

 tion to that which is produced in the primary. It is well known 

 that the disruptive dischai'gc which takes place in a secondary 

 coil only appears in the form of a spark in breaking contact with 

 the primary ; but if the ends of the terminal wires of a secondaiy 

 coil rest on a piece of bibulous paper saturated with a solution 

 of iodide of potassium, the iodine will be evolved at one tei'miual 

 on making, but considerably more at the other on breaking- 

 contact. In describing the terminals as positive or negative, it 

 must therefore be understood that the positive is that at which 

 the iodine is evolved at breaking, and remains cool in the dis- 

 charge throughout while the negative attains a red heat. 



I have been thus particular in the description, because the 

 heating of the positive electrode in the voltaic battery is in itself a 

 curious ph?enomenon long since observed (Phil. Mag.l838,p.436), 

 and the cause of which has not as yet been satisfactorily explained. 



4. If the discharge is taken between two metallic or two char- 

 coal balls in the vacuum of a good air-pump, the effects are very 

 marked ; the lower half of the negative ball is surrounded by a 

 bright, blue glow, while from the positive proceeds a clear, 

 bright, red stream of light. As the vacuum becomes more per- 

 fect this increases in brilliancy, until the dark space is left 

 between the red flame and blue glow, as in Mr. Grove's original 

 experiment, while the negative wire is surrounded with the 

 glow, the intensity of each light increasing in proportion to the 

 vacuum. Where the negative wire is sealed in a glass tube 

 having only its section exposed, the dark space is no longer per- 

 ceptiblcj as also noticed by Mr. Grove. 



5. The wires were attached to my double plate gold-leaf electro- 

 scope, the plates of which are 8 inches in diameter ; these were 

 separated about 0*4' of an inch, the leaves of the electroscope 

 attached to the outside terminal of the coil diverged at an angle 

 of 45°, and the discharge took place with a loud snap, the air 

 between the plates being charged and discharged as a Leyden jar. 



