320 WRITINGS OF JOSEPH HENRY. [1855- 



ho wever we place a non-conductor (for example a cake of bees- 

 wax) under the feet, the whole of the charge will probably 

 not be withdrawn but shared with the body, and the leaves 

 will only partially converge. It may also be shown by the 

 same instrument that in order to produce electrical excite- 

 ment by friction, it is only necessary that two dissimilar sub- 

 stances be rubbed together, one at least of which must be a 

 partial conductor. For example, if while a person is stand- 

 ing on a cake of bees-wax he place one finger on the knob of 

 an electroscope and another person strike him on the back 

 with a silk handkerchief, the leaves will instantly diverge, 

 showing that the whole body has received a charge of elec- 

 tricity, which is prevented from escaping into the floor by 

 the interposed non-conducting bees-wax. 



After the introduction of furnaces for heating rooms by 

 warm air, the public was surprised at exhibitions of elec- 

 trical excitement which previously had not been generally 

 observed. If our shoes be very dry and we move over the 

 surface of the carpet with a shuffling motion on a very cold 

 day, (particularly in a room heated by a furnace,) the friction 

 will charge the body to such a degree that a spark may be 

 drawn from the finger, and under favorable circumstances 

 a jet of gas from a burner may be thus ignited. There is 

 nothing new or wonderful in this experiment; it is simply 

 an exhibition of the production of electricity by friction, 

 which only requires the carpet, the shoes, and the air to be 

 dry, conditions most perfectly fulfilled on a day in which the 

 moisture of the air has been precipitated by external cold and 

 its dryness increased by its passage through the flues of the 

 furnace. In the ordinary state of the atmosphere, the elec- 

 tricity which is evolved by friction is dissipated as rapidly 

 as it is developed, but in very cold weather the non-conduct- 

 ing or insulating power of the air is so much increased that 

 the electricity which is excited by the almost constant rub- 

 bing of bodies on each other, is rendered perceptible. Every 

 person is familiar with the fact that on removing clothes, or 

 shaking garments in cold dry weather, the electricity evolved 

 by the rubbing exhibits itself in sparks and flashes of light. 



