C|)t popular Science 0t 
AND 
BOSTON JOURNAL OF CHEMISTR 
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Volume XXIV. 
BOSTON, MAY, 1890. 
ivfi/M: 
BER.5. 
CONTENTS. 
Familiar Science. — Simple Scientific Experi- 
ments 65 
How Old is tlie World.' 66 
The Dwellings of the Indians of New Mexico 67 
The Dodder 67 
The Pearl 68 
Crocuses 68 
Agricultural Items 68 
Practical Chemistry and the Arts. — Gela- 
tine and Its Uses 69 
The Two Forms of Phosphorus 6g 
A Recent Invention in Photography ... 70 
To Detect Metallic Silver in the Presence of 
Lead 70 
Industrial Memoranda 70 
The Out-Door World. — A Successful A. A. 
Convention 71 
A Prize Worth Trying For 71 
Exchange Notice 72 
A Course in Botany 72 
The Gray Memorial Botanical Chapter . . 72 
A Pair of Colorado Robins 72 
The Spring Prelude 72 
Kditorial. — A Magic Square 5,400 Years Old 74 
Brief Studies in Biology 74 
Meteorology for March, 1S90 75 
Astronomical Phenomena for May, 1890 . . 75 
Coco, C.icao, and Coca 76 
The Chigger 76 
Literary Notes 76 
Medicine and Pharmacy. — The Rational Use 
of Medicine 77 
Nasal Catarrh 77 
An Instrument for Forcing Artificial Respira- 
tion, with an Account ol^ its Successful Use 
in Opium Narcosis 78 
Monthly Summary of Medical Progress . . 79 
Publishers' Column 80 
Ban^iliar Science. 
SIMPLE SCIENTIFIC EXPERIMENTS. 
ELECTRICITY. 
The illustration shows an amusing and 
instructive experiment in electric fishing, in 
Fig. 1. 
which a pencil serves for a rod, a piece of 
thread for a line, and a bent pin for a hook, 
while the bait is composed of a small lump 
of sealing-wax, which is melted around the 
head of the pin, as shown in the lower 
corner of the engraving. The fish should be 
about an inch long, and cut from thin tissue 
paper. If, before exhibiting the experiment, 
the wax is briskly rubbed with a piece of 
woolen cloth, sufficient electrical excitation 
will be produced to cause the fish to "bite'' 
very readily, and remain attached to the hook 
for quite a while. It is hardly necessary to 
say that the "bait" should always be pre- 
sented to the head of the miniature fish ; 
otherwise, the unusual phenomenon of a 
fish biting with its tail might be illustrated. 
MAGNETISM. 
Take a pair of iron tongs and a knife, and, 
holding them as shown in the engraving, ruli 
the knife-blade briskly with the end of the 
tongs, taking care to rub only in one direc- 
tion — towards the point of the knife. When 
the point is reached, the tongs must be lifted 
back towards the handle, and the motion 
repeated. The knife should be occasionally 
depth of focus of the eye is greatly improved. 
Objects can be placed very near to the eye 
and seen plainly, while, if viewed in the 
usual way, they would be very indistinct. 
At the same time, distant objects can be seen 
Fig. 2. 
Jturned over, so that the friction may be 
applied to both sides. In about a minute the 
knife-blade will be found to be magnetic, and 
capable of supporting a needle or steel pen, 
and the magnetism is quite permanent. The 
point of the blade corresponds to the north 
pole of the magnet. The cause of this phe- 
nomenon is not quite clear, and it is worthy 
of further investigation. 
optics. 
Take a piece of cardboard or opaque 
paper, and pierce a small, clean-cut hole 
through it, about the diameter of the head 
of a large pin. The proper size is easily 
found in one or two trials. On holding the 
opening before the eye and looking through 
it, the first eflect noticed will be that the 
Fig- 3- 
with perfect clearness, and the eftect of the 
minute opening placed before the eye is 
exactly the same as when a .photographer 
puts a small diaphragm, or "stop," in front 
of his objective : greater depth of focus and 
clearness of definition, but a loss of illuniinat- 
.ing power. 
A more curious experiment may be shown 
by holding the card between the eye and a 
strong light — a lamp-shade, for instance, or a 
window-curtain through which the light is 
shining. Then hold a pin between the eye 
and the hole in the card, as shown in Fig. 3. 
The head of the pin will be quite visible, but 
reversed, as sliown in the small illustration. 
The cause of this appearance is explained in 
the accompanying diagrams of the eye (Fig. 
4), where i represents the experiment under 
ordinary conditions : the rays of light from 
the pin are refracted by the lenses of the eye 
so that they cross each other, giving a re- 
versed image on the retina. In fact, we 
really see everything upside down, and it is 
probably only on account of long experience 
that we perceive objects in their natural posi- 
tion, just as the photographer soon forgets 
that the images formed on the ground glass of 
his camera are reversed, but selects his points 
