THE MICROSCOPE. 207 
in spite of a flood of medium one side of the mount, if there is a 
scanty supply of medium on the opposite side, or unless the medium 
is very thick, when it requires considerable heat or pressure to get 
the covers down—a process which thin covers and frail or delicate 
specimens could not endure. 
CLIPPING COVERS. 
When it is necessary to use clips, I make them out of brass 
wire not thicker than No. 23 nor thinner than No. 25, Stubb’s wire 
gauge, and bend it in the form of the letter U, so the shortest 
branch is from five-eighths to three-quarters of an inch long, while 
the other is a quarter inch longer. This is bent at right angles so 
as to stand upright, when both branches lie flat on a table. The 
other end should be bent so as to bear on the cover with its end 
transversely.* 
These clips are very simple, and one can be made in twenty or 
thirty seconds. Clips two or three inches long must be made of 
heavier wire, from No. 20 to 16. It has been said that clips should 
have a large ring at the end to bear on covers, to keep them from 
springing, or getting dished on top. When the ring is about as 
large as the covers, and the specimen considerably smaller than the 
covers, as is frequently the case, the cover is just as likely to spring 
and get convexed on top; and as the medium contracts or shrinks 
more under the edge of the cover than in the center, this convexity 
is increased until the covers crack or separate from the medium. In 
either case the mount is ruined. When covers are slightly dished 
in clipping them, the unequal contraction of the medium under the 
covers will flatten them straight and even across the top—probably 
more so than those not clipped at all. 
CENTERING AND RINGING CLIPPED COVERS. 
I lay two strips of pasteboard on the turn-table for the slide to 
rest on, while centering the cover, and then spin the medium around 
the cover, which can be accomplished while the turn-table is 
revolving quite slowly, but not as perfectly as without clips; still it 
will be in a far better condition to lay away to harden, when 
centered, ringed and cleaned as well as convenience will permit. 
One painful sight is to see the covers on slides inclined like a shed 
roof. I have overcome this evil by moving the clip about on the 
cover on turn-table, till it would run as true asa top. They don’t 
all remain so when hardened, but the most of them do, I think. 
Shed-roof covers on hardened slides can be levelled on the turn- 
* The tension can be increased or diminished at pleasure by springing together or 
spreading them. 
