514 ELECTRICITY. 



charged in the ordinary way by using the balls of the dis- 

 charger, a bright spark will pass. Unscrew then one of 

 the balls, charge the jar again, and attempt to dis- 

 charge it by bringing up the point to the knob of the jar. 

 It will be found that the rapid passing off of the electrici- 

 ty through the point, will prevent any spark. 



4. 'Take a small lock of cotton, extend it in every di- 

 rection as much as may be practicable, and by means of 

 a linen thread, about five or six inches long, or by a 

 thread drawn out of the same cotton, tie it to the end of 

 the prime conductor ; then let the electrical machine be 

 put in action, and the lock of cotton, on being electrified, 

 will immediately swell out, by repelling its filaments from 

 each other, and will stretch itself towards the nearest 

 conductor. In this situation, the machine continuing in 

 action, present the end of a finger, or the knob of a wire, 

 towards the lock of cotton, and this will then immediate- 

 ly move towards the finger, endeavoring to touch it. But 

 take a sharp pointed needle in the other hand, and pre- 

 sent its points towards the cotton, a little above the end 

 of the above-mentioned finger, and you will find that the 

 cotton immediately shrinks upwards, and moves towards 

 the prime conductor. Remove the needle, and the cot- 

 ton will corne again towards the finger. Present the 

 needle, and the cotton will shrink again ; which clearly 

 shows that the needle, being sharp pointed, draws off the 

 electric fluid from the cotton, and puts it in a state of be- 

 ing attracted by the prime conductor ; which effect can- 

 not be produced by a wire having a blunted end, or a 

 round ball for its termination.' 



5. Lightning ruds. The philosophy of lightning rods 

 is very evident from the foregoing remarks. The rod it- 

 self forms a conductor from the top of the house to the 

 ground, and by being terminated above by sharp points, 

 the electricity of the cloud is drawn off silently. When- 

 ever a thunder cloud passes a house which has a light- 

 ning rod, the fluid passes down the rod constantly in a 

 silent and harmless stream. So great is this effect, that 

 it is aaiil that HI a large city like London where there are 

 many lightning rods, the thunder showers lose half their 

 violence. When the cloud, which, as it passes over the 



