144 ANNUAL OF SCIENTIFIC DISCOVERY. 



toward the stellar regions. He started from the point, that only one 

 eighth or tenth of the light- is available to the vision in the best achromatics. 

 The observations and trials confirmatory of this were made by means 

 of a Dolland telescope, of thirty-four inch aperture. The importance 

 of the conclusion, if correct, at which he has arrived, lies in this : 

 that a prospect thus opens of effecting a great penetrative or visual 

 power in the telescope, by the employment of eye-pieces truly achro- 

 matic, as by enlarging the object-glass with the ordinary eye-pieces. The 

 chromatic aberrations of converging or diverging refractions, it may be 

 easily made to appear, can be completely eliminated by two lenses of 

 the same kind of glass ; or, probably, by the two surfaces of a single 

 lense of considerable thickness. The other, or field aberration, it is 

 true, will remain for objects upon which the telescope is not truly cen- 

 tred ; but, since the employment of regular equatorial motions, this 

 last has ceased to possess its former importance in a scrutiny of minute 

 points of sight. 



NEW REFLECTING TELESCOPE. 



A NEW reflecting telescope has recently been constructed by Mr. J. 

 Lyrnan, of Lenox, Mass., and by him exhibited at the American Asso- 

 ciation, Albany. The focal length of the instrument is sixteen feet ; 

 aperture, nine and a half inches at the clear. The tube is composed 

 of thick Russia iron, the parts being fastened together by brass bands 

 with screws. The arrangement of observation is that of Herschel and 

 Lord Rosse ; the finder being placed on the left of the front end of the 

 instrument, (left to the person facing the object viewed,) and the eye- 

 piece on the right. The lower end of the instrument has attached to 

 it a frame-work, terminating in Ys, and resting upon two pivots at the 

 ends of a horizontal axis. In the centre of this axis is a socket, work- 

 ing upon a vertical axis, rising from the centre of a tetrapod, which 

 rests upon the ground or floor of the observatory, as the case may be. 

 The front end of the telescope is supported by two legs, lengthened or 

 shortened at pleasure, by a combination of cranks, cords and pulleys ; 

 the whole so contrived as to allow of every necessary motion with 

 smoothness and uniformity, without any cramping of the parts. With 

 this mounting, the instrument may be either portable or stationary. 

 In the latter case, declination and azimuth, and even hour circles, may 

 be used in connection with the foot-piece, if desired. One of the pecu- 

 liarities of this instrument is, that the large speculum is held in its 

 position by a system of triangles, so arranged as to produce perfectly 

 uniform pressure upon the lower surface ; and even the slight pressure 

 requisite is mainly counteracted by an antagonist pressure upon the 

 face. The great excellence of this telescope, however, lies in the re- 

 markably accurate figure of the speculum. The singularly sharp out- 

 line of the stellar discs, the great clearness of the components of almost 

 the closest double stars, seem to evince entire absence of spherical 

 aberration. Indeed, the figure must be a very close approximation to 

 the parabolic curve, if it is not the very curve itself. 



Prof. Caswell, of Brown University, writes to Silliman's Journal re- 



