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Scientific Proceedings, Royal Dublin Society. 



the field of view — say, even two or three degrees out of the 

 centre — the particular division on the card which is seen imprinted 

 on the object still gives its correct bearing. 



Plate XII. shows the appearance of the instrument in its 

 complete form. 



a, Piece of parallel glass coated on its upper side with sulphide of lead, b, Silvered 

 glass mirror, c, Frame carrying tinted glass to reduce brilliancy of image of land- 

 scape if desired, d, A lens whose focus is equal to the radius of the compass-card 

 /, /, Plain glass window. 



