Journal of Applied Microscopy. 



117 



many objects are to be designated on 

 the same slide. 



By imagining- a compass dial to be 

 centered upon the cover-glass, with 

 North at the top, the location of any 

 object can be stated off-hand and instan- 

 taneously, and with definiteness enough 

 for all low and medium powers. Every- 

 thing in the general direction from the 

 center to the top would be North 

 (recorded as "N."); and by glancing over 

 that portion of the slide any object tol- 

 erabb' easy to recognize can be promptly 

 found under any power up to two-thirds, 

 and with a little adroit manipulation up 

 to one-fifth. In cases of special difficulty, 

 and often with higher objectives, a medi- 

 um power should be used as a finder, as 

 in other methods. By designating the dis- 

 tance from the center by tenths (esti- 

 mated) of the radius, further definiteness 

 is and should be attained with no appre- 

 ciable trouble. Thus an object stated to 

 be at "N. 5" would be half-way from 

 center to top; at "E. 9" would be at the 

 right and near the circumference; and 

 at "N. E. 3" would be on a radius mid- 

 way between the two former and about 

 one-third of the way out. This locates 

 the radius near which the object lies, to 

 about one-eighth of the circumference, 

 or 45°; which is good for low powers, or 

 for points near the center, but not pre- 

 cise enough for high powers working 

 near the circumference of lai-ge mounts. 

 Of course these angles can be subdivided 

 by combining the letters to make 16 

 points of 22*° as "W. N. W.;" but few 

 persons could do this without some 

 possibility of confusion. 



The clock-face, a somewhat more 

 familiar object, gives greater precision 

 by dividing the circumference into 12 

 segments of 30° each; the principle is the 

 same, the directions being given by the 

 hour figures, and the distances of radius 

 by decimals; a system successfully used 

 in designating instantly the location of 

 the bullet holes made in target shooting, 

 except that there the radial distances are 

 given by concentric circles. Here the 

 top becomes 12, the bottom 6, and inter- 

 mediate 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 nine-tenths out, or identical with the 

 "E.9" of the compass method. By the 

 clock method the hour spaces can be 

 readily halved by the eye, giving 24 

 segments of only 15° each. It might be 

 seen that an object was at the right of 

 12, but not as far as 1, giving 121; while 

 the pointer in the cut would, without the 

 aid of the figures, be recognized as about 

 midway between 12 and 3 o'clock, corres- 

 ponding with "N. E." of the compass; 

 so that "14, 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 directions almost as ac- 

 curately 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. Experts 

 would omit the "." after "N," etc. The 

 contraction "o'c." may be added to the 

 record, to indicate the clock method, as 

 "3,9 o'c"; but it is unnecessary, as these 

 entries have no likeness to the double 

 lines of the Maltwood system. 



If instrumental precision be desired, it 

 can be secured by carefully centering 

 the cover-glass around the optical axis 

 of the microscope, and then, with the 

 goniometer ocular or with the gradua- 

 tions of the concentric revolving stage, 

 measuring from this center the angular 

 distance of the object above or below 

 the longitudinal axis of the slide; and 

 then measuring with the ocular micro- 

 meter the linear distance from the cen- 

 ter of revolution. Thus an object at the 

 right and 60° below the axis would be a 

 5 o'clock, one at the left and 30° above 

 the axis would be a 10 o'clock, while 

 the minute hand, being about 47° 

 above the right, would be about a half- 

 past one, as already seen. By this 

 means the object can be easily located 

 within a single degree; but that is sel- 

 dom, if ever, necessary, as sufficient 

 accuracy for the cases to which this 

 method is applicable can be gained, 

 almost automatically after a little prac- 

 tice, by comparison with the picture of 

 the dial "in the mind's eye." 



R. H. WARD. 

 Troy, N. Y. , 



New Form of Photo-Micrographic Camera 

 and Condensing System. 



E. B. Stringer (Journal Royal Micro- 

 scopical Society, 1898, pp. 174-179) brought 

 before the Royal Microscopical Society a 

 form of apparatus for high-power photo- 

 micrography which possesses novel fea- 

 tures, and is very convenient in use. 

 The rear part of the camera extends by 

 means of sliding brass tubes, so that 

 both when at its shortest and longest 

 focus there is no projecting baseboard. 

 A door is provided at the side of the 

 camera for forcusing the image on a 

 white card in situ, and the whole camera 

 can be drawn backwards for looking 

 down the microscope when in position, 

 or for screen projection. 



Mr. Stringer avoids vibration by 

 clamping down nothing, and by support- 

 ing the apparatus on layers of cork and 

 felt. The microscope has a tripod 

 support, the feet of which pass through 

 holes in a triangular brass adjusting 

 plate onto a cloth-covered board 

 beneath. The focusing is by an endless 



