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NOTES AND CORRESPONDENCE. 
Mr. Warington’s Portable Aquarium Microscope.—There is, 
perhaps, no department of microscopic investigation so inter- 
esting to most observers as the development, growth, and 
habits of vital organisms. The aquarium has now become 
popular, and thrives in the homes of many who do not pre- 
tend to cultivate science; but how often do we find that it 
is unaccompanied with any adjunct for assisting the eye to 
scrutinise the form and structure of its living tenants. Much 
of the interest and mental recreation which a study of the 
details of these remarkable beings will afford is lost, for 
want of that indispensable appendage, a simple form of 
microscope easy of application. To the ingenuity of Mr. 
Warington we are indebted for an instrument (described in the 
present ‘ Journal’) which meets all the requirements of the 
case, being cheap, simple, and not lable to get out of order. 
By reason of the position and other conditions under 
which the objects to be observed are situated, there will 
oftentimes be much difficulty in throwing light upon them, 
particularly when object-glasses of the shortest practicable 
focus are employed; for most frequently they require to be 
viewed as opaque objects. I therefore offer some suggestions, 
which I trust may lead to others of greater value. 
If the aquarium, glass tank, or live-box, with its fluid 
contents, be considered as a square prism, it will be seen that 
aray of light incident upon any one of its four plane sur- 
faces, may be thrown back again from the adjoining plane in 
various directions, within the angle of total reflection. We 
may sometimes avail ourselves of this fact for the illumination 
of an object in a peculiar position. Leta aa represent the 
glass sides of an aquarium, 6 the surface of the water. The 
object to be viewed at c, with the object-glass (d). If the 
rays from a lamp be thrown in the direction shown, by means 
of the condensing-lens (e), after passing through the first 
surface they will be refracted more towards the perpendicular, 
and on reaching the glass wall of the tank will be reflected 
back again on the object at c. It may be mentioned that 
the total reflection of the rays takes place from the outer 
surface of the plate glass; therefore, if a small specimen is 
situated in close contact with the imner surface, it may be 
found that there is ample space in the thickness. of the plate 
