NOTES AND MEMORANDA. 
99 
Resolution of Surirella gemma. — M. Adolf Schultze publishes 
the following note in ' Science Gossip ' for July : — " The resolution of 
this diatom is not so much a matter of magnification as one of illumi- 
nation ; whether the J- ^^^^ your correspondent will show the 
markings depends upon its quality, its correction, and upon the illu- 
mination used. A good ^ inch, inch, inch, or y^^ inch, will show 
these markings beautifully, but it is quite possible that the ^^^^ ^^^^ 
not do so, although it ought. I have, for instance, not resolved the 
lines into heads yet with my g^^- inch, whilst my Eoss's yL inch shows 
them splendidly. T use the narrow side of the flame of a paraffin lamp, 
place a bull's-eye condenser with its convex side next to it, and obtain 
thus parallel rays on the mirror or on the rectangular prism. I always 
interpolate a blue light modifier. Very oblique rays being essential 
for the resolution of Surirella gemma, a large dark-ground spot or 
rectangular stop of the condenser must be employed, and the latter, 
of course, must be racked up rather high. I have, however, obtained 
the best results by the use of one of Wenham's paraboloids. I put 
the dark-ground stop flush with its apex, and place this about J inch 
below the object. By changing the position of the mirror or rect- 
angular prism slightly, the true appearance as well as Hartnack's 
false ones, which Dr. Carpenter has figured, are easily obtained. If the 
lamp is placed in front of the microscope and the light passed through 
a bull's-eye condenser directly in the condenser or the paraboloid, 
the definition is still further improved. The use of monochromatic 
sunlight facilitates the resolution greatly. Owing to the shape of 
Surirella gemma, only a portion of the frustule can be resolved at 
one time without altering the focus." 
The Aquarium Microscope at Berlin.— The aquarium microscope 
is a feature which we trust Mr. Kent will introduce at our Westminster 
tanks. An instrument of this kind has been established at the 
Aquarium at Berlin by Dr. Zenker. In fact, there are more than 
fifty instruments in this institution, which are by the well-known 
makers, Beneche, Hartnack, Schmidt, and Haensch. Dr. Zenker has, 
we believe, already given lectures on the different microscopic speci- 
mens of the Aquarium by the aid of the oxy-hydrogen lamp and 
microscope. 
Professor Huxley on the 'Challenger's' Work.— At the dinner 
which was given to the ' Challenger's ' staff the other day. Professor 
Huxley delivered a capital speech, in proposing the health of the 
scientific staff. Among other things, he said,* " Take, again, the 
marvellous discovery that over large areas of the sea the bottom is 
covered with a kind of chalk, a substance made up entirely of the 
shells of minute creatures — a sort of geological shoddy made of the 
cast-off clothes of those animals. The fact had been known for a 
long time, and we were greatly puzzled to know how those things got 
to be there. But the researches of the ' Challenger ' Lave proved 
beyond question, as far as I can see, that the remains in question are 
* Vide ' Nature,' July 13. 
