Hie Influence of the Antijpoint, By E. M. Nelson. 271 



With my own apparatus the identical hair drawn by Mr. 

 Gordon (figs. 47 and 48) gives these results : — 



Dark ground, W.A. '97 = -0000394 in. 

 Bright „ „ '47= '0000275 m. 



The thicknessof this hair obtained from these data is * 0000356in. 



The antipoint value for W.A. 1*0 derived from Mr. Merlin's 



measurement of the hair is '000004486, that from my own 



measurement is * 000003776, and that published in my " Table " 



Journ. E.M.S., 1903, p. 581) is -00000404— this last being obtained 



from data given by the extinction of a " black dot." 



The mean of these three values, viz. ■ 00000410, may be accepted 

 as being very near a true value for practical use, and the accompany- 

 ing Table is calculated upon this assumption. 



It is remarkable that there should be so close an agreement in 

 the values of antipoints calculated from data obtained from such 

 different sources. 



The amplifier described by Mr. Merlin was used in the measure- 

 ment of the hair. 



Table showing the Amount of Correction to be applied to the 

 Apparent Measurement of Minute Microscopic Objects. 



The correction for objects measured on a bright ground is + 



dark „ — 



* Number of waves to the inch. 



U 2 



