Juny 12, 1918] 
patiens Balsamina and Tropwolum majus. 
There can be no doubt, therefore, as to the 
eause of the disease, and land on which any 
of the common Solanaceous plants have wilted 
should not be planted to Ricinus, unless it is 
known positively that the wilt was not of 
bacterial origin. Dwarfing is usually the first 
sign of the disease in seedling Ricinus plants. 
Erwin F. Sirs, 
G. H. Goprrey 
Unitep STaTEs DEPARTMENT OF AGRICULTURE, 
July 1, 1918 
CELLULOID LANTERN-SLIDES 
LANTERN-SLES made by the simple process 
of merely drawing or writing with ink on thin 
sheets of celluloid are often useful in pre- 
senting to an audience simple diagrams and 
sketches, tabulated data, mathematical expres- 
sions, et cetera. 
Some years ago Mr. E. D. Tillyer, one of 
my colleagues at the Bureau of Standards, told 
me of slides that had been made by tracing on 
sheets of gelatine, which were afterwards 
bound between plates of glass to keep them 
flat. I found these of great use in illustrating 
a lecture with diagrams that I copied from 
published articles—far more convenient than 
blackboard sketches or large paper charts. 
But the method is subject to three somewhat 
annoying defects: 
(1) Continual clogging of the pen and 
spreading of the ink while tracing a drawing, 
(2) impossibility of making inconspicuous 
erasures, (3) necessity of binding each tracing 
between two sheets of glass. The first two 
defects were removed by substituting for the 
gelatine a less soluble material, the third by 
constructing a set of glass pockets into which 
the slides could be slipped. 
A slide of simple character can be made by 
writing or sketching directly upon the sheet 
of celluloid, using an ordinary steel pen of 
proper fineness, with india or colored ink. 
More complicated drawings and diagrams from 
publications are most easily made by tracing. 
Mistakes may be erased by wiping with damp 
cloth or paper. For firm, smooth lines of uni- 
form thickness the ordinary draftsman’s tools 
SCIENCE 
43 
are needed: straight edge, French curves, 
ruling pen, and compass pen. Very fine lines 
are produced by scratching the surface with a 
needle point. Although scarcely visible on the 
slide, these will show up black and sharp when 
projected on the screen. Typewriting directly 
on the celluloid also projects well. 
Other transparent materials can, of course, 
be used instead of celluloid. Gelatine yields 
fairly good slides but is difficult to work be- 
cause of its solubility. Even tracing cloth 
and waxed paper are usable; although their 
limited transparency produces a rather dark 
field, and the texture of the material shows 
plainly. 
To fit the standard 33 inch & 4 inch lantern- 
slide cover-glasses the celluloid should be trim- 
med to 8 X 33 inches. During the process of 
tracing, it is more convenient to have the 
celluloid somewhat larger than 3 384 inches 
to allow sufficient margin for holding it 
against the original by means of thumb-tacks 
or a paperweight. The margins may be trim- 
med later, leaving the drawing centrally lo- 
cated on the slide. 
A glass pocket to hold celluloid slides in the 
projecting lantern is easily made from two 3} 
< 4 inch lantern-slide cover-glasses. These 
are held apart by strips of card, 7/32 inch wide 
and somewhat thicker than the celluloid, 
pasted along the entire length of each short 
edge and along an inch or so at each end of 
one of the longer edges. The glass plates are 
bound together by strips of black paper pasted 
over the edges as in making an ordinary lan- 
tern-slide, except that the binding is omitted 
where the separating strips of card are absent. 
The longer edge that is entirely free from 
binding forms the top of the pocket; the 
central opening left in the opposite edge is for 
inserting a piece of card to eject the celluloid 
slide when it can not be shaken out. Both of 
the longer edges of each glass are ground 
smooth and are somewhat beveled on the sides 
that form the interior of the pocket, so as to 
facilitate insertion and removal of the cellu- 
loid. A small white lable in an upper right- 
hand corner serves as a thumb mark for guid- 
ing the lantern operator. 
