178 THE NATURE STUDY COURSE. 



and in a watch. Simple examples are the windlass of the well- 

 digger and the capstan of the house-mover or anchor-raiser. 



Every farmer's boy is familiar with the pulley in the "block 

 and tackling" of the horse-fork. City pupils often see cranes and 

 derricks in use to move heavy merchandise or building material. 



Loading-planks, hillside roads and stairways are inclined 

 planes. When the inclined plane moves against the weight it 

 is called a wedge. The wedge used in cleaving wood consists 

 of two inclined planes back to back. Axes, knives, chisels, 

 jack-planes, and needles apply the principle of the wedge. If 

 the inclined plane winds spirally around a cylinder the 

 machine is called a screw. The screw-nail, boring auger, letter- 

 press and cider-press are examples. 



Now and again the teacher will witness or hear of some 

 circumstance that may open the way to teach a lesson in 

 physical science as for example, when it was reported that one 

 of the girls had dropped her brooch in a cistern, the loss was 

 made the opportunity to give an elementary lesson on reflected 

 light. A hammer that fell in a well while a man was repair- 

 ing the cover was brought to the surface by a magnet. The 

 circumstance was related during the Nature Study period and 

 the interest it excited was utilized in the teaching of a lesson. 



A picture fell because a pupil tied a " granny " knot on the 

 hanging cord. The accident started a series of short lessons 

 and exercises that ended after a week or two in a knotting 

 competition. The honor of being most expert was awarded to 

 the one who could make the longest cord out of ten pieces, 

 each four inches long, strong enough to hold up a fruit basket 

 filled with bricks, and at the same time have the greatest 

 variety of knots in it. It is worth while to know how to tie a 

 shoelace properly, and to tie a horse safe to a post by a rope 

 that is to go around his neck. It takes some thinking to tell 

 why one knot holds while another nearly similar one slips. 

 The teacher who knows the topic and knows his profession can 



