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Prof. "W. II. Miller on a new Form of 



possible to eliminate some sources of error, and to render the 

 observations more accurate than with the other reflective 

 goniometers in ordinary use, and in some instances to obtain 

 the means of making observations otherwise impracticable. 

 Besides, the construction of the new form is simple, and does not 

 demand any great nicety of workmanship, except of course in 

 the graduation of the circle and verniers. The instrument, made 

 by Messrs. Troughton and Simms, has for its support a tripod 

 with level! ing-screws, carrying a fixed disk 200 millims. in 

 diameter and 5 millims. thick, tapped for screws at the points 

 D, E, F, Gr — by which supports for the vertical mirror, tele- 

 scope, &c. mentioned later on can be attached to the instrument, 

 in a circle concentric with the disk, having a radius of 88 

 millims., the diameters through those points making angles of 

 45° and 32° with a fixed diameter of the disk. The graduated 

 circle, also 200 millims. in diameter and 8 millims. thick, is 

 divided on its edge into spaces of 20 / each, the degrees being 

 numbered up to 360°, is read off to 20" by each of two 

 verniers H, K attached to the circular plate, and is provided 

 with a clamp and slow-motion at L. It is tapped for screws 

 at the points M, N, 0, P distant 90° from one another, and 

 about 19 millims. from the edge of the circle. A circular 

 disk 100 millims. in diameter, and 8 millims. thick, is tapped for 



