ASTRONOMICAL TELESCOPES — PEASE 209 



storms sweoj) the surface. These storms, called sun spots, are so huge 

 that tlie earth would be lost in some of thorn. 



Those of us who sj^end not only the long watches of the night but 

 weeks of nights exposing the same plate upon the same object realize 

 what a great boon it would be to obtain these same photographs in 

 a much shorter time, or rather to spend the same time upon a spec- 

 trum of greater scale or upon fainter stars and nebulae about which 

 we have comparatively little direct knowledge. No search for the 

 polo could be of more interest to the explorer than are the ])roblems 

 of celestial objects to the astronomer. Many of them are so far 

 away that our telescopes are not powerful enough for us to decide 

 whether they are clusters or nebulae, but we shall not rest satisfied 

 until we learn their true character. Back in the sevonloentli century 

 Hevelius made drawings of the moon, engraving nearly 100 of them 

 on copper plates himself, showing the moon at its various phases. 

 Note the accuracy of his drawing, Plate 4, Figure 1, so far as general 

 features are concerned, the streaks radiating from some of the crat- 

 ers, the dark seas, the mountain ranges, and compare them with our 

 Ijost photographs to-day. We will admit that the photographic por- 

 trayal of the moon's features is splendid and that when we look at 

 an individual crater such as Copernicus the amount of detail is great. 

 But imagine that we could step into Jules Verne's projectile and 

 pay a visit to the moon, see it closely with its rills and valleys, its 

 craters and mountain peaks. Would it not be worth the while? 

 Actually we can not do this at present, but we may get all the 

 thrills by building a telescope of greater aperture which will bring 

 the image of the moon nearer to us. 



For many years we have been studying the problems of very large 

 telescopes. With the interferometer we have examined atmospheric 

 disturbances over regions 20 feet in diameter and can definitely say 

 that there is ver}^ little difference in the effect on the image between 

 beams of starlight 4 feet apart and 20 feet apart. Experience in 

 building our present machines and designing still larger ones shows 

 that the construction of such telescopes is, with all the increased 

 facilities of to-day, but a piece of straightforward work, no more 

 difficult than were others in their day. 



Machine shops are equipped with tools of ample capacity to finish 

 all required parts of large size or weight. Powerful cranes will lift 

 our materials and place them at our command. Precision bearings 

 of a size we need have already been tried on our 14-inch seacoast guns 

 and found to stand all that we ask of them. Many times you have 

 seen trucks, carrying large safes and castings, guns, and turbines, 

 rolling along our streets as though the movement of a weight of 

 100 tons were an ovory-day affair. A dome of any size is fabricated 

 as easily as our large steel buildings or ships. Its movement on 



