62 THE ANATOMY OF SCIENCE 



11, where and P represent the knots, A, B and 

 C the beads. At the end of a minute we lower the 

 photographic plate one centimeter and open 

 the shutter again, thus giving upon the same 



Figure 10 



plate the picture OT'. At the end of the second 

 minute we repeat the process, getting the pic- 

 ture 0"P", and so on. Or we might have left the 

 shutter open and moved the plate steadily at the 

 rate of one centimeter a minute, in which case 

 the beads would have traced continuous lines 

 upon the plate, such as A A' A", B B' B". Now 

 when we examine the plate we see that the bead 



