62 THE EYE. 



They also painted spots of different colors on the oppo- 

 site sides of the cards, in order to see what compound color 

 would be produced in blending them by the twirling of the 

 card. The boys spent two whole days, during which they 

 were confined within doors by rain, in making a number 

 of these cards of various styles and patterns. They made 

 them to carry home with them to America. Lawrence 

 highly approved of this amusement. He said that such 

 cards were worthy of being regarded with special respect, 

 in view of their being capable of fulfilling a double func- 

 tion. They were equally adapted to interest children as 

 amusing toys, and philosophers as articles of apparatus il- 

 lustrating the persistence of vision. 



