DISCOVERIES IN THE CELESTIAL SPACES. 701 



already for two years constructed similar instruments, through 

 industry and thought.'' Zacharias Jansen, (who like Lip- 

 pershey, was a spectacle-maker at Middleburg), invented, in 

 conjunction with his father Hans Jansen, towards the end of 

 the sixteenth century, and probably after 1590, the compound 

 microscope, the eye-piece of which is a concave lens ; but, as 

 we learn from the ambassador Boreel, it was not until 1610 that 

 he discovered the telescope, which he and his friends directed 

 to distant terrestrial, but not toward celestial objects. The 

 influence which has been exercised by the microscope in. 

 giving us a more profound knowledge of the conformation 

 and movement of the separate parts of all organic bodies, 

 and by the telescope in suddenly opening to us the regions of 

 space, has been so immeasurably great, that it seems requi- 

 site to enter somewhat circumstantially into the history of 

 these discoveries. 



When, in May, 1609, the news of the discovery made in 

 Holland of telescopic vision reached Venice, Galileo, who w r as 

 accidentally there, conjectured at once what must be the 

 essential points in the construction of a telescope, and imme- 

 diately completed one for himself at Padua.* This instrument 



* The above-named physician and mathematician of the Margravate 

 of Ansbach, Simon Marius, after receiving a description of the action of 

 a Dutch telescope, is likewise believed to have constructed one himself 

 as early as the year 1608. On Galileo's earliest observation of the 

 mountainous regions in the moon, to which I have referred in the text, 

 compare Nelli, Vita di Galilei, vol. i. pp. 200-206; Galilei, Opere, 

 1744, t. ii. pp. 60, 403, and (Lettera al Padre Cristoforo Grienberger, 

 in materia delle Montuosita delta Luna, pp. 409-424.) Galileo found 

 in the moon some circular districts, surrounded on all sides by moun- 

 tains similar to the form of Bohemia. " Eundem facit aspectum Lunse 

 locus quidam, ac faceret in terris regio consimilis Boemia}, si montibus 

 altissimis, inque peripheriam perfect! circuli dispositis occluderetur 

 undique" (t. ii. p. 8). The measurements of the mountains were made 

 by the method of the tangents of the solar ray. Galileo, as Helvetius 

 did still later, measured the distance of the summit of the mountains 

 from the boundary of the illuminated portion, at the moment when the 

 mountain summit was first struck by the solar ray. I find no obser- 

 vation of the lengths of the shadows of the mountains. He found the 

 summits " incirca miglia quattro " in height, and " much higher than 

 the mountains on our earth." The comparison is remarkable, since, ac- 

 cording to Riccioli, very exaggerated ideas of the height of our mountains 

 were then entertained, and one of the principal or most celebrated of 

 these elevations, the Peak of Teneriffe, was first measured trigonometri- 



