denominated the Aerial Reflector. 47 



the fitting up of the joint and stand requisite for supporting and 

 steadying so unwieldy an instrument. While the one instru- 

 ment would require two persons to carry it from one room to 

 another, and would occupy a considerable portion of an ordinary 

 apartment, the other can be moved, with the utmost ease, to any 

 moderate distance, and the space it occupies is scarcely known. 



2. It is more convenient ^br viewing celestial objects at a 

 high altitude than any other telescope. — When we look through 

 a Gregorian reflector, or an achromatic telescope of 4 or 5 

 feet in length, to an object elevated 50° or 60° above the ho- 

 rizon, the body requires to be placed in an uneasy and dis- 

 torted position, and the eye is somewhat strained, while the ob- 

 servation is continued. But, when observing similar objects 

 by the Aerial Reflector^ we can either stand perfectly erect, 

 or sit on a chair, with the same ease as we sit at a desk when 

 reading a book or writing a letter. In this way, the sur- 

 face of the moon, or of any of the planets, may be contemplated 

 for an hour or two, without the least weariness or fatigue. A 

 delineation of the lunar surface may be taken by this instrument, 

 with more ease and accuracy than with any other telescope, as 

 the observer can sketch the outline of the object by one eye, on 

 a tablet placed a little below the eye-piece, while the other eye is 

 looking at the object. For the purpose of accommodating the 

 instrument to a sitting or a standing posture, I caused a small 

 table to be constructed, capable of being elevated or depressed 

 at pleasure, on which the stand of the telescope is placed. When 

 the telescope is 4 or 5 feet long, and the object at a very high 

 elevation, the instrument may be placed on the floor of the apart- 

 ment, and the observer will stand in an erect position. 



3. This instrument is considerably shorter than a Gregorian 

 telescope, whose large mirror is of the same focal length. When 

 an astronomical eye-piece is used, the whole length of the instru- 

 ment is nothing more than the focal length of the speculum. 

 But a Gregorian, whose large speculum is 4 feet focus, will ex^ 

 ceed 5 feet in length, including the eye-piece. 



4. The " aerial reflector"" far excels the Gregorian in bright- 

 ness. The want of light in Gregorians is owing to the second 

 reflection from the small mirror ; for, it has been fuUy proved by 

 experiment, that, about the one-half of the rays of light which, 



