148 SCIENTIFIC RECREATIONS. 



or concave mirror, of converging to a focus the rays of light falling on it from 

 any object, and at that point or focus forming an image of the object. 

 The following diagram will illustrate this. Let VW be a lens, and AB 

 an object between the glass, and F the focus. The ray, Ac, is so refracted 

 as to appear to come from a. The ray from b likewise appears in a similar 

 way, and a magnified image, ab, is the result (fig. 152). 



The ordinary Telescope consists of an object-glass and an eye-lens, with 

 two intermediates to bring the object into an erect position. A lens brings 

 it near to us, and a magnifier enlarges it for inspection. We will now give 

 a short history of the Telescope and its improved construction. 



Roger Bacon was supposed to have had some knowledge of the Tele- 

 scope, for in 1551 it was written : " Great talke there is of a glass he made 

 at Oxford, in which men see things that were don." But a little later, 

 Baptista Porta found out the power of the convex lens to bring objects 

 " nearer." It was, however, according to the old tale, quite by an accident 

 that the Telescope was discovered about the year 1608. 



Fig. 152. Converging rays to a focus. 



In Middleburg, in Holland, lived a spectacle-maker named Zachary 

 Jansen, and his sons, when playing with the lenses in the shop, happened 

 to fix two of them at the proper distance, and then to look through both. 

 To the astonishment of thfe boys, they perceived an inverted image of the 

 church weathercock much nearer and much larger than usual. They at 

 once told their father what they had seen. He fixed the glasses in a tube, 

 and having satisfied himself that his sons were correct, thought little more 

 about the matter. This is the story as told, but there is little doubt that 

 for the first Telescope the world was indebted either to Hans Lippersheim 

 or Joseph Adriansz, the former a spectacle-maker of Middleburg ; and in 

 October 1608, Lippersheim presented to the Government three instruments, 

 with which he " could see things at a distance." Jansen came after this. 

 The report of the invention soon spread, and Galileo, who was then in 

 Venice, eagerly seized upon the idea, and returning to Padua with some 

 lenses, he managed to construct a telescope, and began to study the heavens. 

 This was in 1609. Galileo's Tube became celebrated, and all the first 



