128 
quarter of our century,—the post-Pasteur 
period. 
But in the last analysis it is the higher sig- 
nificance of bacteriology which must always 
be regarded as its most important charac- 
teristic. By virtue of the discoveries upon 
which it was founded, to which it has led and 
upon which to-day it rests illustrious and se- 
cure, mankind has been enabled for the first 
time to arrive at an adequate comprehen- 
sion aud understanding of the microscopic 
world and of many important and familiar 
natural phenomena hitherto either not 
understood or misinterpreted. The origin 
of bacteriology is interesting and instruc- 
tive ; its scope is broad and comprehensive ; 
but these matters are of only moderate 
consequence as compared with its philo- 
sophical significance. At the beginning of 
our century, in absolute ignorance of bac- 
teriology and its wonderful teachings, man 
gazed with wonder or indifference on some 
of the most familiar, yet most mysterious, 
of natural phenomena. Organic matters al- 
most everywhere slowly ‘ decayed’ and dis- 
appeared ; sweet and sugary fruit juices 
‘turned’ rapidly and ‘spontaneously ’ into 
pungent or acid liquors; slow and innocuous 
‘decomposition’ often gave place to foul 
‘putrefaction’ and rapid ‘decay’ or destruc- 
tive ‘rots’; manure applied to land, even 
to land lying fallow, soon vanished alto- 
gether; ‘epidemics, ‘plagues’ and ‘ pesti- 
lences’ swept over the earth, and man could 
neither understand, nor explain, nor intel- 
ligently fight them; the microscopic world 
quivered with forms of life which seemed 
to be born in a day and to disappear like 
dew. The heavens had long since revealed 
the glory of God, and the firmament,— 
thanks to the interpretations of Coperni- 
cus, Galileo and Newton,—had abundantly 
shown his handiwork. But the microscopic 
world still sat in the shadow of darkness, 
awaiting the disclosure of its meaning. 
At last, in the fulness of time and largely 
SCIENCE. 
[N.S. Vou. XIII. No. 317. 
through the achromatic objective, a great 
light shone upon and from the under world. 
The mysteries of fermentation, putrefaction, 
organic decomposition, decay and the min- 
eralization of organic matters were reduced 
to their lowest terms and brought into line 
with other problems of biology. Epidemics, 
plagues and pestilences were proved to be 
merely the ravages of micro-parasites ; the 
life of the under world was scrutinized, clas- 
sified and studied, and has been found to 
follow in general the same natural laws as 
that of the upper world. Bacteriology has 
given to us a comprehension of the under 
world similar to that which astronomy and 
astro-physics have given us of the heavens ; 
the widely-accepted theory of present-day 
spontaneous generation has been proved to 
be amyth, and with the fading out of this 
ancient view of nature the last traces of 
medieval ideas of magic, alchemy and easy 
transmutation of the elements have dis- 
appeared from science. 
WitiiAM T. SEDGWIcK. 
MASSACHUSETTS INSTITUTE 
or TECHNOLOGY. 
CERTAIN STROBOSCOPIC PHENOMENA IN THE 
END-ON PROJECTION OF A SINGLE WAVE. 
In projecting a plane polarized wave ma- 
chine wave, ww, with a lens on a distant 
screen, S, one observes when the wave is in 
vigorous motion that the balls appear on 
the screen as stationary objects, symmet- 
rically disposed with reference to the axis 
of advance of the wave, or the direction of 
incident light, ZL, and at distances apart 
corresponding to equal phase-differences. 
Clearly the same effect must be produced in 
rotating the circle of reference, C; if pro- 
vided with balls, a, b, c—at equal angular 
distances apart on the circumference. As 
certain parts of this phenomenon are pe- 
culiar, I constructed a disk like C by sold- 
ering bright rods at right angles to its sur- 
face at a, 6, c—with an axle at C. 
