NATURAL HISTORY MISCELLANY. 189 
senting the different countries chiefly interested, any movement, 
if made at all, in reference to it, should be a concerted movement 
in England, Germany, France, if practicable, and this country, the 
same lenses being sent for study from one country to the other. 
Microscopists might thus be informed, not as to which objectives 
are the “best,” but as to which desirable qualities are possessed 
in an eminent degree by the lenses of the various makers.—R. 
H.W. 
Eyesight AND THE Microscorpr.—In using the microscope I 
have found that the best system is that recommended by Dr. Car- 
penter, who has probably had as much experience in this matter 
as any person I know of. It is to alternate the use of the eyes, 
always keeping the unemployed eye open. But I feel confident 
that it is of no use to keep the unemployed eye open if it be made 
to stare at a dead-black surface. It is the exclusion of light from 
one eye, and the consequent unequal action of the visual organs, 
that is thus produced, that causes the mischief that we dread ; 
and it matters not whether this unequal action be produced by 
covering the eye with the eyelid, or by excluding the light from it 
by other means,—the result is the same. In making observa- 
tions with the microscope, all extraneous light should be excluded 
from the eyes. Hence the value of a properly arranged shade. 
Such a shade, however, should consist of more than a mere flat 
sheet of pasteboard covered with velvet. It should have a per- 
pendicular portion, rising up in front of the face, and cutting off 
all light except that which comes through the microscope. And 
now, having provided a shield of this kind, which, by the way, is 
easily made of pasteboard blackened on the inside with dead- 
black varnish (made of alcohol, lamp-black, and a very little 
shellac), if we punch an inch hole at such a point that the unoc- 
cupied eye can see it in the same way that the other eye looks 
through the instrument, we will find that the fatigue experienced 
by that eye is vastly less than when it is exposed to the dead- 
black surface. A few trials will set at rest all questions on 
this head, and the change from light to darkness is easily made 
by simply slipping a piece of blackened paper or card over the 
hole. 
With few exceptions, we use altogether too much light with the 
microscope. Where a full flood of light is passed through a 
