Keiv Outlines of Chemical Philo<;ophy.^ 343 



In keeping a register of the variable action of M. Dp Luc's 

 columns, some attention is necessary in adjusting the pendulums 

 to the maintaining power; for if the pendulums be too long, or 

 too heavy, tiieir vibrations will be irregular, stopping at intervals 

 till the columns have accumulated sufficient power to put them 

 again into motion. If the columns be sufficiently powerful to 

 keep heavy pendulums in regular action when the weather is 

 cold, their vibrations will agree very nearly with the temperature 

 of the air at ail other seasons; but if the pendulums be very 

 short, they will vibrate too quickly for observation. 



The two elements which keep tiic ])endulu:ns in motion come 

 from the earth ; for when the electiometer is placed in contact 

 with the copper extremity of the series of columns, no action is 

 produced ; but when a person standing on the floor lays Ins 

 linger upon the zinc extremity, the pendulums will instantly 

 begin to vibrate, and continue in motion as long as the com- 

 munication with the earth shall remain in the same state. The 

 electrometer being removed to the zinc extremity, no action 

 will commence ; but let a communication be made between the 

 copper extremity of the series and the earth, and the pendulums 

 will vibrate as freely as befoie. 



Although the two elements which ):°ep the pendulums in mo- 

 tion come from the earth, yet the variable state of the earth's 

 electricity has no efl\3ct upon them, for they will make the same 

 number of vibrations in a given time, the temperature of ihe 

 air being the same, whatever tiie electrical state of the earth 

 may be. 



It is well known to every electrician that his machine acts 

 much better at one time than at another. This has been attri- 

 buted to various causes; but the true one is, the electricity of 

 the earth is variable, not only on diiferent days, but at different 

 times in the same day. 



The method that I use for determining this property of the 

 earth, is very simple, and yet it admits of considerable accuracy. 

 1 take a barouietcr tube about two feet long, and after having 

 drawn it once through a piece of silk held in my hand, I hold it 

 over one of my phial electrometers, at the distance of about an 

 inch. 



If the leaves of the electrometer diverge and remain perma- 

 nent, the angle which they contain is measured, and noted down 

 as the electri al state of the earth at that time. If the leaves 

 I)e not permanently electrified with the tube at that distance, it 

 is brought into contact with the electrometer, when a perma- 

 nent effect will generally be produced ; and the angle, being 

 measured, is entered in a column titled contact. But it will 

 sometimes happen, that the earth contains so little electricity, 

 Y 4 that 



