250 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK m. 



of many other scientific discoveries ; only, in this case, we may be 

 certain that the idea of combining lenses to form a telescope does 

 not belong to ancient times, or even to the middle ages. The first 

 mention of it is towards the end of the sixteenth century, when 

 Porta found that by combining two lenses, the one concave and the 

 other convex, "near, as well as distant objects could be magnified 

 and rendered distinct." But it was a Middelburg optician, Jean Lip- 

 pershey, who was the first to realise this combination, and constructed 

 the first telescopic lens (1606). Jacques-Adrien Metius in 1608 and 

 Galileo in 1609 appear to have solved independently Porta's optical 

 problem ; but it must be said that the great physicist and astronomer 

 of Florence had heard of Lippershey's discovery without having had 

 any exact account of the instrument itself. 



Now, how did the Dutch optician discover this ? On this point 

 nothing is positively known, as is proved by the fact that there are 

 two versions two different legends on the subject. According to 

 Arago these are as follows : 



Hieronymus Sirturus relates that a stranger, either man or demon, 

 presented himself at Lippershey's and ordered several convex and 

 concave lenses. On the day agreed upon he called to fetch them, and 

 chose two, one concave and the other convex. After having looked 

 through them and by degrees separated one from the other without 

 saying whether he did this in order to test the work of the artist or for 

 any other reason, he settled his account, and disappeared. Lippershey 

 forthwith set about imitating what he had seen, noticed the magnifi- 

 cation induced by the combination of the two lenses, fixed the two 

 glasses at the extremities of a tube, and hastened to offer the new 

 instrument to Prince Moritz of Nassau. 



According to the other version, Lippershey's children playing in 

 their father's shop, bethought themselves to look through two lenses, 

 one convex, the other concave ; these two glasses being placed at a 

 proper distance, showed the weather-cock on the Middelburg steeple 

 magnified and brought nearer. The surprise of the children having 

 awakened Lippershey's attention, he, to make the experiment more 

 conveniently, at first attached the glasses to a plank ; afterwards he 

 fixed them to the extremities of two tubes which slid one into the 

 other. From this moment the refracting telescope was discovered. 1 

 1 Arago, Astronomic Popalaire. 



