Micrometric Correction for Minute Objects. By E. M. Nelson. 581 



assuming that the W. A. was "8, we have from column 1 the 

 ■correction • 00000505 to be added to each of those measurements ; 

 this gives ■ 00000993 OrooVoo) f° r the size of the fiagellum, and 

 •0000539 (y§35o) f° r fcne diameter of the termo. Fig. 141 is a dia- 

 grammatic representation of Dr. Dallinger's measurements enlarged 

 20,000 times. Fig. 142 is the same after the correction has been 

 .applied ; it will be noticed that the body of the termo is increased 



Table showing the Amount of Correction to be applied to the 

 Apparent Measurement of Minute Objects. 



t Number of waves to the inch. 



by 10 p.c, and that of the fiagellum by 100 p.c. From this it 

 will be understood how erroneous the micrometric measurement 

 of very minute objects must be, unless some allowance has been 

 made for the influence of the antipoints by which the magnified 

 image is formed. 



The figures in the above table give the size of the antipoint 

 and indicate the minimum visible for objects on a bright ground. 



* On account of the super-amplification of those layers of an object which are 

 not strictly in focus, and also on account of irradiation, the apparent measurement 

 of objects on a dark ground is not to be relied upon, so this correction, which for 

 objects on a dark ground is only a rough approximation, will not be needed. 



