1898.] MICROSCOPICAL JOURNAL. 151 



one could be almost instantly found with a one-fifth 

 objective. This locates the radius near which the object 

 lies, to about oue-ei^ht of the circumference, or 45 deg. 

 Of course these angles can be subdivived by combining 

 the letters to make 16 points of 22^ deg, as " W. N. W." 

 for example, but few personscould do this without some 

 possibility of confusion. 



The clock-face, a somewhat more familiar object, gives 

 greater precis^ion by dividing the circumference into 12 

 segments of 30 deg, each. The principle is the same, 

 the directions being given by ihe hour figures, and the 

 distance of radius by decimals ; a system successfully 

 used in designating instantly the location of the bullet 

 holes made in target shooting, except that the radial 

 distances are given by ruled circles. Here the top 

 becomes 12, the bottom six, and intermediate points by 

 the familiar directions of the clock-face. Thus the 

 " 3, 9 " location would be at 3 o'clock, to the direct 

 right and 9-lOths out, or identical with the "E9" of 

 the compass method. By the clock method the hour 

 spaces can be readily halved by the eye, giving 24 seg- 

 ments of only 15 deg. each. It might be seen that an 

 object was at the right of 12, but not as far as 1 giving 

 12| ; while the pointer would, with the aid of the figures, 

 be recognized as midway between 12 and 3 o'clock, cor- 

 responding with N. E. of the compass ; so that *' li, 3 " 

 here would be identical with "N. E. 3" of the other. 

 With a very little practice one will recognize the 4 and 5 

 o'clock direction almost as accurately as the 3 or 6; and 

 the location of dozens of small shells, scales, or other 

 objects can be recorded almost as fast as the numbers can 

 be written. 



If instrumental precision be desired, it can be secured 

 by centering the cover-glass around the optical axis of the 

 microscope, and then, with the goniometer ocular or 

 with the graduations of the concentric revolving stage. 



