OF ARTS AND SCIENCES. 3G5 



Many advantages will be apparent on comparing such a mounting 

 with an equatorial. Great steadiness would be secured, since the 

 mirror would be the only portion moved, and this would be placed di- 

 rectly upon a low pier. Instead of a large and expensive dome which 

 is moved with difTiculty, the mirror would be protected by a small shed, 

 of which the roof could be easily removed. It would, therefore, be 

 opened and ready for use in a very short time, and would quickly take 

 the temperature of the surrounding air. The object-glass would be 

 mounted directly upon a second pier, and, as it would not be moved, 

 would be in very little danger of accident. The tube could be made 

 of tin or other inexpensive material, as its flexure is of no importance. 

 It could easily be protected from the changes of the temperature so 

 troublesome in the tube of a large equatorial. If preferred, it might 

 even be exhausted of air, or filled with hydrogen, and the effect of the 

 changes of temperature thus greatly reduced. 



The eyepiece could be mounted on a third pier, and would be so far 

 distant horizontally from the mirror and object-glass that there is no 

 reason that it should not be enclosed iu a room which may be warmed. 

 The comfort in winter of working in a warm room will be appreciated 

 by those who have used a large telescope in a cold climate. The re- 

 sult is sure to be an increased precision in the observations, and a possi- 

 bility of prolonging them over longer intervals. A similar effect is 

 produced by the constant direction of the line of sight. No esi^ecial 

 observing chair is needed. There is no limit to the size of the attach- 

 ments which may be made to the eyepiece, since they need not be 

 moved. This is a great advantage in certain spectroscopic and photo- 

 metric measurements. A strong wind interferes seriously with many 

 observations, as it is impossible to make a telescope so stiff that it will 

 not be shaken by sudden gusts. In the plan here proposed the mirror 

 alone is exposed, and its surface is too small to give trouble. 



By means of a long handle the position of the mirror may be regu- 

 lated from the eye-end, and the declination of the object observed read 

 by small telescopes. If the mirror can be moved at right angles to 

 the meridian 5° from its central position, an object at the equator may 

 be followed for forty minutes, and other objects for a longer period. 

 Without this motion an object may be followed for three or four min- 

 utes by moving the eyepiece alone. Clockwork may be applied to the 

 mirror, or less easily to the eyepiece. The focal length may be 

 increased almost indefinitely if desired, and certain advantages will be 

 thus attained in the diminution in the defects of the object-glass, 

 although those of the reflector will not be affected. If the telescope is 



