May 23, 1884.] 
are parallel with its equator, the axial extremities 
become well-defined poles. 
Place the equator of the sphere, the light, and the 
eye, in the same plane, and the axis of the sphere 
vertical to it. Make the reflective angle as acute as 
possible. The reflection is a central luminous point 
Fig. 3. Fie. 4. 
at the equator in a vertical band terminating acutely 
toward either pole, fig. 3. If the reflective angle is 
about 90°, the reflection is crescentic, fig. 4. When 
the sphere is placed remote from the light and the 
eye, with its axis inclined toward the light, the re- 
se is a luminous point at its proximal pole, 
g. 5. 
If the sphere is brought’ nearer the light, thus 
increasing the reflective angle, a short curved tail de- 
Fig 6. 
Hse. 5. 
velops, fig. 6. This increases in length as the sphere 
is approached to the light, until, at close proximity, 
a, in fig. 7, results. Removal of the reflecting surface 
at any latitude on the sphere interrupts the reflection, 
as atc, fig. 7. The interposition of a comparatively 
small opaque body before the light, when the inclined 
sphere is in very close proximity to the light, divides 
the reflection, — a, b, fig. 7. Multiple sources of light 
multiply the reflections, which describe different 
curves, all radiating from, though not always reach- 
Ing, the pole. The greater the sphere in relation to 
the source of light, the more perfectly the form of 
the luminous point is reflected. If circular, it appears 
as a disk or brilliant nucleus. The extension of the 
reflection toward the equator constitutes a diverging 
train or tail. 
Fig. 7. 
Fie. 8. 
Changes in the positions of the three factors pro- 
duce a limitless variety of figures, which are sugges- 
tive of various cometic forms: for instance, fig. 8, 
two opposite spherical sectors, the analogue of figs. 1 
SCIENCE. 
617 
and 2, The resemblance of the reflections to cometic ap- 
pearances is increased if the striated reflecting sphere, 
with the inclined axis maintained, is made to describe 
about a light approximately the form of a comet’s 
orbit; then all the changes exhibited by a comet, 
from the first nebulous point to the fully-developed 
tail, are illustrated upon its surface, including the 
changes in the position of the tail in relation to the 
light, which occur during the small curve of a comet’s 
orbit. The reflections describe all the radii between 
a and }, fig.9. Itis surprising to what extent cometic 
behavior may be illustrated upon the polished spheres: 
position, elongation, abbreviation, disappearance, an- 
nular images, irregular images, are all quite possible. 
Fig. 9. 
If an hypothesis may be ventured, it is briefly this: 
if a sphere of meteoric dust of a diameter exceeding 
the greatest length of the comet’s train, having an 
axial rotation and inclination, does actually traverse 
the comet’s orbit, such a rotation would convert its 
superficial inequalities, varying densities, and possi- 
bly its individual atoms, in effect, into continuous 
striae, parallel with its equator; and such inclination 
would place it in position to reflect the images which 
comets display. Discussion of the hypothesis is re- 
served. Gro. O. WILLIAMS, M.D. 
Greene, N.Y. 
THE BIOLOGICAL INSTITUTE AT 
; PHILADELPHIA. 
Not a few of the readers of Science are 
looking upon the new departure in biology in 
Philadelphia with high hopes that it may 
become one of our most valued possessions. 
They regard it as a new and therefore great 
opportunity. But they will be sadly disap- 
pointed if its officers give themselves up largely 
to merely routine teaching, or are satisfied in 
taking a position towards biological science in 
any large degree conservative. ‘The United 
States is a poor field, or is rapidly becoming 
so, for the perpetuation of ancient methods in 
one of the youngest and most vigorously grow- 
ing of the sciences. And if any one cares 
to profit by experience, let him reflect upon 
those steps, which, within ten years, have led 
up to one of our most valued institutions, — 
the Johns Hopkins university, — or to the al- 
most incredible success of the Naples station. 
Broadly speaking, their conditions of prosper- 
ity have been two, — on the one hand, money ; 
