THE WOODWARD ILLUMINATOR. 179 



in such cases, in common with the modified " reflex," 

 its action, to some extent, is crippled; nevertheless, 

 nice resolutions are to be obtained with either instru- 

 ment, with either of which we are able to instantly 

 display the transverse stride of amphipleura pellucida, 

 frustulia saxonica, etc. The simplicity of Dr. Wood- 

 ward's device, its ease of working, and the facility it 

 affords for the comparison of objectives are in them- 

 selves strong points in its favor, and to these may be 

 added the satisfactory character of the resolutions ob- 

 tained. We gladly accord to Dr. Woodward our appre- 

 ciation of the value of his illuminator. 



We are informed by General Cox that the pin hole 

 apertures are only used when working with sunlight 

 illumination ; they also serve a useful purpose as an assist- 

 ance in measuring with greater precision the obliquity 

 of the illuminating pencils employed, thus enhancing 

 the value and capacity of the instrument. 



TOLLES' TRAVERSE LENS. 



It now remains to present to the reader the Tra- 

 verse Lens, devised by Mr. R. B. Tolles. The follow- 

 ing is the inventor's own description of this valuable 

 accessory, and is taken from the American Journal of 

 Microscopy : 



"With the advent of objectives of jncreased interior 

 angle aperture, the indispensableness of equivalent ac- 

 cessory means for the illumination of the object became 

 immediately evident.* 



* See"M. M. J.," July, 1871, p. 38. 



