250 GENERAL SCIENCE 



the heavy charge in an approaching cloud by sending 

 off a continuous stream of charged particles of air. If a 

 lightning rod is not a good conductor the induced charge 

 on the building may become so great that it attracts 

 the charge in the cloud. The spark coming from the 

 cloud, being very large, will then suddenly rush to the 

 ground over the lightning rod and may melt the rod and 

 set fire to the building. 



There is no need of being afraid during an electric 

 storm. It is no safer in a closet or a darkened room 

 than it is in daylight or in a well-lighted room. 

 Usually the safest place during a thunder shower is 

 near the middle of a room. To get under a tree stand- 

 ing in an open field is of course dangerous, because the 

 tree is the only tall object around. If a flash comes in 

 that direction the tree will be apt to conduct it to the 

 ground. It is not so dangerous to stand under trees in 

 the woods where there are many trees as it is to stand 

 under one tree in an open field during a thunder 

 shower. 



173. Current Electricity. --To understand what makes 

 the electric current flow, let us use what we learned about 

 temperature and the flow of liquids. Heat will flow 

 from an object with a high temperature to an object of 

 low temperature regardless of the quantity of heat in 

 either. If two objects of different temperature are 

 placed together, the cooler one will receive heat from the 

 warmer one. In the case of liquids, water will flow from 

 a high vessel into a low one if they are connected by a 

 tube, even though the low vessel may have ten times as 

 much water in it as the higher one. The water in the 

 high vessel has a greater downward pressure than the 

 water in the low vessel, hence the flow is in the direction 



