Marce# 7, 1884.] 
arrow. As fast as the ring enters the space abe, it 
becomes red-hot and non-magnetic, and a lack of equi- 
librium is thus maintained which results in a continu- 
ous rotation. 
The motion is necessarily quite slow on account of 
the considerable time required to heat the iron ring. 
In the actual experiment, moreover, considerable 
difficulty was experienced from the distortion which 
the ring underwent when softened by the heat, in 
consequence of which the speed of rotation became 
very irregular. With a permanent steel magnet, a 
speed of about one revolution in two minutes was 
obtained; and with a powerful electro-magnet, a 
weight of six grams was raised fifty centimetres in 
six minutes, and, in a second experiment (the ring 
having become quite distorted), ninety centimetres 
in thirty minutes. 
Of course, the source of energy is the Bunsen burn- 
ers; and the experiment leads at once to the fact, that 
the specific heat of magnetized iron is greater than 
that of unmagnetized. CHAs. K. McGEE. 
University of Michigan, 
Ann Arbor, Feb. 19. 
Congenital deafness in animals. 
The communication of Professor Bell in No. 54 of 
Science, in reference to Mr. Lawson Tait’s statement 
that no other animals than cats are affected with 
congenital deafness, calls to my mind the fact, that 
in my early boyhood I had a dog which was thus 
afflicted. I got him when a puppy; and, so far as we 
could determine, he was never able to distinguish any 
sounds. He was of the breed usually known as ‘ fist,’ 
and, so far as my memory serves me, was of a yellow 
color: certainly he was not pure white. What ren- 
ders this instance the more interesting, is the further 
fact, that a playmate of mine also had a deaf dog. I 
think he was of the same family, but not, I believe, 
of the same litter. That congenital deafness should 
be rare among wild animals, I can readily under- 
stand, since, in the struggle for existence, their 
defect would lead to an early extinction; but under 
domestication, where their conditions approach more 
nearly to those of man, I can see no reason why a 
defect of physical organization should not be trans- 
mitted by inheritance, as I believe it to have been in 
the cases above cited. It is a fact well known to 
aurists, that in some families there is a tendency 
to become hard of hearing, or even deaf, at about 
the same age; owing, doubtless, to certain evolutions 
which take place in their physical structure at that 
time. Swan M. BuRNETT, M.D. 
Washington, Feb. 22. 
A singular optical phenomenon. 
The windows of our office are provided with fly- 
screens having the ordinary mesh of something less 
than an eighthof aninch. Thirty feet across the way 
is a building whose windows are protected by acoarse 
sereen having a mesh a little less than half an inch 
in size. Standing about ten feet back from and 
looking through the fly-screen at the coarse screen, 
an inverted, magnified image of the latter is seen in 
mid-air, between the observer and the fly-screen; the 
inversion, of course, being only detected by the ap- 
parent movement made by the image on changing the 
position of the eyes. The explanation of the phe- 
nomenon is not difficult. The lines of the coarse 
screen throw nominally a single ray of light, which is 
inverted through the particular mesh of the fly-screen 
directly in line with it and the observer. Any other 
substance, such as a paper wad introduced in the 
coarse screen, will not appear in the image. It may 
SCIENCE. 
27d 
not be uninteresting to mention in this connection the 
fact, that while a short-sighted person, to whom I en 
deavored to show the same phenomenon in my home, 
using as an object the slats of a blind in a house 
a hundred and fifty feet away, was unable to see 
the actual slats, owing to their remoteness, their 
image was distinctly visible to her. Bod, 8; 
Deflective effect of the earth’s rotation. 
In a letter of mine, published jn Science, ii. No. 26, 
I suggested that the deflecting force produced by the 
rotation of the earth on bodies moving on its surface 
is not wholly represented by the rotation of a tangent 
plane, but depends, in part, on the centrifugal force 
resulting from the body’s relative motion in longi- 
tude, and is therefore greatest when the motion is 
perpendicular to the meridian. 
That my suggestion is not true, and that the force 
is the same for all directions of the motion, may be 
demonstrated very simply, as follows: — 
From the proposition announced in section 25 of 
Peirce’s ‘ Analytical mechanics,’ it follows that any 
tangent plane whose latitude is 4 rotates about an 
axis normal to that plane with an angular velocity 
equal to w cosec. A, w denoting the angular velocity of 
the earth about its polar axis. 
Therefore if P represent the point where the nor- 
mal axis pierces the surface of the sphere, and if a 
body be caused to move in any direction over the 
point P with a velocity v, it will, by the rotation of 
the tangent plane, be constrained to describe in space 
the spiral of Archimedes, whose equation is w= aé; 
and when @ = 27, u =v multiplied by the time of one 
rotation of the tangent plane. Hence, if one hour 
be the unit of time, u = 24» cosec. 4; and $a, = the 
radius of curvature at the origin of the spiral, = 60 + 
7 sin A, 
Now, the deflecting force at P is equal to the cen- 
trifugal force due the velocity v at the origin of the 
spiral, which is represented by v? + 3a: 
A ef, = a0 SIMA; 
But the centrifugal force, V2 + R, due the rota- 
tion of the earth at the equator, is known to be 
zag mg; mg denoting the weight of the body, and 
V = -by T R e 
Ma soe 0 2 oe Sia As 2 he 
whence, substituting for V’, we get, 
ps ze mg 24% sin aA 
hisalay 
The centrifugal force resulting from the body’s 
relative motion in longitude affects only the origin 
of the spiral, and not at all its elements, and hence 
has no influence on the value of /: consequently f is 
the total deflecting force, and is independent of the 
direction of the motion. J. E. HENDRICKS. 
Des Moines, Io., Feb. 14. 
A. carboniferous genus of sharks still living. 
I observe that in a late number of Science, Mr. Gar- 
man describes a new genus of sharks from the Japan- 
ese Seas, under the name of Chlamydoselachus. The 
figure of the teeth which he gives shows the animal 
characterized by Mr. Garman to be a species of the 
genus Didymodus (Cope, Proceedings Philadelphia 
Academy, 1883, p. 108, equal to Diplodus Agass. Poiss. 
fossiles, pre-occupied in recent fishes), which has 
hitherto been supposed to be confined to the carbo- 
niferous and Permian periods. The species possess 
two, three, or four denticles. Material in my pos- 
session enables me to fix the position of this genus, 
which I will endeavor to explain in the next (April) 
number of the American naturalist. Didymodus 
