bringing him to the eyepiece which commands any point in the celes- 

 tial vault from the horizon to the zenith. 



This magnificent instrument, recently installed, fully meets the 

 most sanguine expectations of its projectors. A few weeks ago it was 

 turned upon the moon, bringing its volcanic cones, its rugged crags, 

 and its seamed mountain ranges within a few hundred miles of the 

 beholder. Then Saturn with its golden rings became the cynosure 

 of all eyes. There the giant planet stood forth, suspended in mid- 

 heaven by an invisible force, its belted surface and its family of 

 satellites a wonderful and tangible reality. But the climax of the 

 occasion was capped when the monster light-gathering power of the 

 great mirror, three times greater than that of its 60-inch neighbor, 

 was turned upon the awe-inspiring Hercules Cluster, revealing thou- 

 sands of suns massed together. A photograph made with a 100-inch 

 telescope reveals about 30,000 stars in this cluster; the brighter ones 

 in the center being widely separated. The invisible ones are only 

 obtainable on long exposure. 



The following account of the 100-inch telescope as published 

 in "Popular Astronomy" and written by Dr. George E. Hale, director 

 of the Mount Wilson Observatory, gives a concise account of this 

 great telescope: 



"After a series of tests extending over several months, the 100- 

 inch telescope of the Mount Wilson Observatory has been found to 

 be a complete success. The construction of this instrument, begun 

 several years ago, was necessarily an experiment, as it was by no 

 means certain, after the optical and mechanical difficulties had been 

 overcome, whether the atmosphere would be sufficiently tranquil to 

 permit clearly defined images of celestial objects to be obtained with 

 so large an aperture. Mount Wilson, situated in the favorable 

 climate of Southern California, where the best of results have been 

 secured with telescopes up to 60 inches aperture, is a site as promis- 

 ing as any that could be found. But as observations with smaller 

 instruments are insufficient to settle the question, the actual per- 

 formance of the telescope could not be predicted with certainty. 



"The tests, which permit the performance of the new instrument 

 to be directly compared with that of the neighboring 60-inch tele- 

 scope, show that the full gain in light gathering power, to be ex- 

 pected from the increased aperture, has actually been attained. The 

 100-inch telescope thus collects nearly three times as much light as 

 the 60-inch telescope, and concentrates it in images so sharp that the 

 gain in brightness is fully utilized. This means that the atmospheric 

 conditions on Mount Wilson have proved to be good enough to meet 

 the very severe demand. 



"The sharpness of astronomical photographs obtained with the 

 100-inch telescope may be judged from some large pictures of the 

 moon, which bring out very small details. These were taken with 

 the combination of mirrors that give the telescope an equivalent focal 

 length of 134 feet. Photographs of small nebulae taken at this 

 focus also show details of structure of, great interest. 



