760 
Notes . 
The following extradl from microscopical observations made 
by Stephen Gray in 1696, and quoted by Mr. W. S. Kent in his 
“ Manual of the Infusoria ” now in progress, would seem to 
foreshadow the important modern discoveries of homogeneous 
immersion and immersion illumination : — “ Having by me a 
small bottle of water, which I knew to have in it some of those 
minute insedts which the deservedly famous observator Mr. 
Leeuwenhoek discovered by the help of excellent microscopes ; 
having seen them with the common glass microscopes, and with 
the first aqueous* as above mentioned, I poured a few drops of 
this water on the table, and taking a small portion thereof on a 
pin I laid it on the end of a small piece of brass wire, of about 
one-tenth of an inch diameter. I continued to lay on two or 
three portions of water, till there was formed somewhat more 
than an hemisphere of water ; then keeping the wire eredt I 
applied it to my eye, and standing at a proper distance from the 
light I saw them and some other irregular particles, as I had 
predicted, but most enormously magnified ; for whereas they are 
scarce discernible by the glass microscopes, or the first aqueous 
ones, within the globule they appeared not much different both 
in their form, nor less in magnitude than ordinary peas. They 
cannot well be seen by daylight, except the room be darkened, 
after the manner of the famous dioptric experiment, but most 
distinctly by candle-light : they may be very well seen by the full 
moon-light, and the pin sometimes takes up the water round 
enough to show its objects distinct.” Here the side of the 
spherule of water next the eye acts as a plano-convex lens, mag- 
nifying the animalcule in the centre of the sphere, the opposite 
half doing duty as an immersion condenser, and here the matter 
rested and was forgotten for one hundred and eighty years. 
The following rough and ready method of cleaning diatoms is 
given in the “American Journal of Microscopy” (ii., 1881, 
p. 93) : — “ A few crystals of bisulphate of potass are crushed, 
and a sufficient portion added to the material to be cleaned. The 
mixture is placed in a hollow scooped in a sound piece of char- 
coal, and heated before the blowpipe until it ceases to fuse 
readily: when the substance appears to be opaque, and of a 
whitish colour, it is to be removed, dropped into a small quantity 
of water, and boiled for a few seconds. The diatoms and sand 
are now liberated, and can be washed and separated by any of 
the usual methods.” It is claimed for the process that it saves 
the troublesome boiling in acid, and that the apparatus and ma- 
terials are easily procurable. 
A spherule of water held in a loop of wire, or a hole in a metal plate. 
