512 PROCEEDINGS OF THE AMERICAN ASSOCIATION 
more distinctly felt in regard to the lower classes of instruments that are 
furnished to be iras and particularly in regard to popularizing the 
Binocular Microscope. 
In exhibiting photographs by Dr. Maddox of the Podura scale, Presi- 
dent Barnard gave an exhaustive review of the discussion in regard to th 
structure of the fine The traditional ‘note of exclamation,” or goose- 
is 
difficult with sufficiently high powers. Professor Smith, of Kenyon Col- 
lege, orta to make the objective its own illuminator. Others have 
replaced the mirror M placed behind the lenses by a plate of glass or à 
prism ; ne all these means P^ a glare of light by reflection from the sur- 
panad the lenses. The speaker had proposed 
mirror behind the outer pair, an in- 
mele abs rkuhn (fig. 100) which works exceed- 
ingly well with medium powers, say one-third 
` Fig. 100. 
- ipiertind in high powers, As ared 
si above the front pair), it Ped more light, and 
illuminates from any part or all parts of the 
circumference at will; on the other hand it is 
ut oe less easily applied, requiring the front lens to 
em ed in glass in : i 
shown in the photographs where the wedge- 
c 
pushing an pasakose far beyond its ordinary power were received with 
general distrust. 
In the itc which followed the reading of this paper, Dr. Ward 
remarked that the production of a beaded appearance, as a purely optical 
effect, should be —À am longer sienne vis rather an occasional 
accident to persons using high powers. As reme instance, in the 
case of a coarse and pisci si ese he aria vm while experiment- : 
ing upon an elater of Marchantia polymorpha, that beautiful double spiral 
