202 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 2 8 



his tower in the hills of Florence, Italy, turned it to the moon and 

 the planet Jupiter, What he actually saw was but little compared 

 with Avhat we see to-day, but it was sufficient to stir the foundations 

 of thought to their very depths. Here was another world with moun- 

 tains and seas like the earth, and here another planet with not one, 

 but four, moons circulating around it. We are likely to think of 

 these developments as ancient history, yet the telescope is a very 

 recent tool of man, its advent being coincident with the settling of 

 America's eastern coast. Sixty-seven j^ears had passed since Cabrillo 

 had sailed these California shores, Pocahontas had just saved the life 

 of Cape. John Smith, and tlie Pilgrims had not j-et embarked in the 

 May-flower when Galileo made his first telescopic observations in 

 January, ]610. 



Telescopes continued to be made, and though there Avas little 

 progress in astronomical observations aside from charting the 

 features of the moon, sun spots, and the like, the telescope itself 

 was developed into a highly useful instrument, a step necessary 

 before its best work could be accomplished. The lens was first 

 mounted at the upper end of the quadrant bar and the eyepiece 

 at the lower end. Thi,s type of instrument necessitated two mo- 

 tions, and it was soon found that by tipping the post to point to 

 the north pole of the heavens, a single motion about the post would 

 keep the star in view, the post now being called the polar axis. 



In this tipped or equatorial instrument the quadrant arm is 

 developed into a tube with an axis through its center. Thi,s axis is 

 called the declination axis and is adjusted once for all. There are 

 many variations in the mechanical forms of the axes. In the 

 English type of mounting, for example, the polar axis is a yoke 

 with bearings at either end, Avith the tube sAvuug between its sides. 

 In the Gei-man type, of which the 86-inch I>iick telescope is an ex- 

 ample, the declination axis is attached to the upper end of the polar 

 axis, the tube being fastened at one end of the declination axis and 

 a counterweight at the other. In the forked type, as illustrated 

 by the 60-inch reflector on Mount Wilson, the upper end of the 

 polar axis above the two bearings is forked, either prong carrying one 

 end of the declination axis. In the turret type of telescope, with 

 which Governor Hartness, of Vermont, has spent man}^ a delightful 

 night, the polar axis is merged into the roof of the observatory, 

 the light being reflected into the turret by a 45° mirror placed at the 

 intersection of the declination axis and the tube. 



Having at first only simple lenses to work with, astronomers found 

 that if they wished to increase the size of the lens they nuist at the 

 same time increase its focal length. One of Huyghens' lenses, for 

 example, was 6 inches in aperture and 210 feet in focal length. These 



