THE BINOCULAR MICROSCOPE. 435 



^seen in a Parallel tube binocular. Dra^Ying3 and pliotomicro- 

 -graplis of many microscopical objects are of little value, the things 



that are vv^anted are models of the structures. We want models 

 of diatoms and models of insect scales. I put forward no definite 

 -opinion upon the structure of the Podura scale, and still keep 

 -^n open mind regarding it ; all that can be said is that this 

 'depression image is a fair description of the appearance of the 

 ^exclamation marks as viewed critically under a Parallel tube 

 i-binocular. The exclamation mark is an enigma still, and no one 



has any pretext for saying, "I know all about the Podura scale, 

 i^or I have examined it under a high-power binocular." 



"Those who have read iwy former paper on binoculars * will 



notice that my views have undergone modification. At the time 

 'of writing it the Parallel tube binocular had been only three months 



in use, but now it has been fairly constantly employed for four 



years. Previously, in company with many other microscopists, 



I was obsessed with the idea of the perfection of the Wenham 



binocular images, and had not adopted at that time the Greenough 

 ;image as a standard for stereoscopism. It will be seen, from 



what has now been written, that the superiority of the images in 

 "the Parallel tube binocular is recognised both as regards their 



sharpness and stereoscopic relief. 



In conclusion, one improvement for the Parallel tube binocular 



anay be suggested, which may with advantage be adopted when 

 •-that instrument is made, let us hope, in this country. At present 



■the tube separation adjustment is effected by rack and pinion, 



wliich is far too quick ; a movement by a right- and left-handed 

 ■ screw would be more delicate and far preferable. I regret that, 

 -owing to my not possessing a Stephenson's binocular, experiments 



with that instrument have not been included, but there is no 

 ixeason to doubt that the results would have been precisely 



similar to those obtained with the Wenham. 



J^Ew Points of Microscopical Interest Brought Forward 



!1. The adoption of the Greenough as a standard for stereo- 

 scopic relief. 



-.* 



Q. M. C. Journ., 1914, vol. xii., No. 95, p. 378. 



