64 NOTES AND MEMORANDA. 
place exhibiting the same phenomenon ; and on the 14th of 
September, 1871, in a small stream about two miles from the 
first locality, I found Gomphonema constrictum, capitatum, 
acuminatum, and cristatum, all growing upon the same stipes 
along with intermediate forms. I took care to deposit speci- 
mens of my first gathering in the cabinet of the American 
Microscopical Society, New York, and, as I have said, the 
specimens I sent Dr. Arnott are in the collection of the 
Quekett Club in London; but as probably Mr. Archer will 
not have an opportunity of visiting either of these collections, 
I will gladly send him specimens, as I have secured a plen- 
tiful supply of all of my gatherings. 
I have in hand the microscopical work of the Geological 
Survey of New Hampshire, and I hope diatomists will be 
glad to hear that I shall ere long go to press with a report 
on the so-called “ infusorial deposits” of that state. I shall 
be at all times glad to furnish specimens to those interested, 
and, in fact, would be pleased to have the names and addresses 
of every one interested in the Diatomacee. 
A. Mrap Epwarps, M.D. 
Newark, New Jersey, U.S. 
Colcured Rings of Crystals as seen through the Microscope. 
—Dr. W. H. Stone has communicated to the Physical 
Society an account of an arrangement for exhibiting the 
coloured rings of uniaxial and biaxial crystals in a common 
microscope. 
The author was not aware that any arrangement had been 
hitherto supplied to the ordinary microscope other than an 
extra top to the eyepiece, containing a supplementary stage 
and an analyser. ‘This could only be considered a clumsy 
expedient. 
The objects to be attained were clearly two—first, to 
transmit the rays at considerable obliquity through the plate 
of crystals; secondly, to gather these up, and form a real 
image within the tube of the microscope. Amici had accom- 
plished this by a special combination of lenses which bears 
his name; it might, however, be done simply by placing a 
screwed diaphragm on the end of the upper draw-tube within 
the body of the microscope. The screw should be that ordi- 
narily used for object-glasses. ‘To this an object-glass of long 
focus was fitted, and another of higher magnifying power in 
the usual place. The whole body was then drawn out and 
adjusted to a telescopic focus on a distant object. The lower 
objective formed the object-glass of the telescope and the 
— objective with the Huyghenian eyepiece a compound 
ocular. 
