434: EDWARD M. NELSON ON 



watch paiuted in Arabic figures, when I have known them a.s= 

 Roman for the greater part of my life. 



It has been found that upon the outside of this diatom the 

 larger areolations belong to the depressed portions, and the smaller- 

 ones to the raised ; of course when an inside view is obtained the 

 reverse is seen. These features have neither been seen, nor could 

 have been found, with a monocular, but when known they can 

 be detected with a Wenham, but it is very doubtful if ever they 

 would have been discovered with that instrument. It is a very- 

 different thing to discover an object whose presence is unknown,, 

 and to find it when one both knows that it is there and knows • 

 what to look for. 



This then is the answer to the question, " What detail has been, 

 discovered with a binocular that has not been seen with a mono- 

 cular ? " It is perfectly certain that this structure would never 

 have been discovered with a monocular. 



Perhaps someone will ask, " "What light does the new binocular- 

 throw upon the interpretation of the Podura scale ? " The Podura 

 scale has undergone a more searching microscopical examination 

 than any other object, and yet it remains the microscopist's. 

 enigma. In a paper on this subject * the various views of several 

 observers were given, besides that of my own, which was that the 

 exclamation mark was a cuniform- shaped elevation and not a 

 plumelet. It has now been examined with an apo . 1/12 of 1 '4 N. A. 

 and No. 18 compensation eyepieces on the Parallel tube binocular.. 

 From an examination of this kind one would have expected an. 

 immediate and decisive answer, but this was not to be had, for 

 the object is a very thin one, and such objects, as has been already 

 pointed out, do not yield much stereoscopic relief. Of course- 

 nothing could be easier with either a monocular or binocular, by 

 means of a small cone, to make a strong image of a raised exclama- 

 tion mark, but would it be a true image ? The evidence supplied 

 by the Parallel tube binocular is that they are depressions. Sup- 

 pose there is a surface of cheese with grooves or furrows, more or 

 less parallel, on it, then if with a cheese-taster some scoops be made 

 in these furrows, with a small and slightly deeper depression at 

 the end, we shall have a rough representation of this object as- 

 ♦ R. M. S. Journ., 1907, p. 393, pi. 16. 



