SCIENTIFIC SUMMARY. 
437 
moves uniformly at such, a speed that the component of water-weight down 
the inclined bed is balanced by frictional drag on the bottom. The fluid in 
the neighbourhood of the stream is known) not to move as a solid mass, the 
centre moving faster than the sides, and the different fluid layers rubbing 
against one another. The adhesion of the fluid to the solid against which it 
moves, also gives rise to sliding or rubbing action. It is desirable to have a 
set of experiments in which the conditions can be varied more than can be 
done by such methods. He thought it instructive to try a limited mass of 
water, and a virtually unlimited surface, such as is given by a disk in rota- 
tion. This apparatus he had constructed. "Within the outer vessel is placed 
a thin copper chamber, the diameter of which is unalterable, but the depth 
variable at pleasure. The disk is placed concentrically within it ; so that 
there are two cheese-shaped masses of water, one above, one below the 
disk, which are dragged into rotation on the side next to it, and retarded 
next the sides of the pan. The couple required to rotate the disks is equal 
to that formed by the disk or fluid when the motion is uniform. Hence the 
tendency of the chamber to rotate is measured by suspending it from a 
trifilar suspension. A weight suspended by a cord measures the force 
required to keep the index at zero. It appears that a rough cast iron disk 
has a frictional resistance almost exactly as the square of velocity ; whereas 
a turned brass disk gives a value of x decidedly less than 2. The resistance 
is a little greater when the mass of water is larger. He proposes to try 
the effect of temperature on fluid friction in viscous as well as in mobile 
fluids. 
Specific Magnetism of Iron — forms the subject of an essay by Dr. 
Auerbach of Breslau. He shows that this is not without influence on the 
galvanic behaviour of the metal. If a current be conducted through an 
iron wire, phenomena appear which do not occur with other metals. The 
following are some of the known facts : — 
(1.) The actual galvanic conductivity has been very variously stated, 
between 12*35, and 15-9 per cent. 
(2.) Resistance increases with rise of temperature. 
(3.) The heat generated by the current, by Joule’s law, is 448*0 as against 
478*9 for copper. 
(4.) On closing the circuit, an extra current takes place in the opposite 
direction ; on opening, in the same direction. 
(5.) Longitudinal magnetization of iron influences its resistance. 
In examining the last (5) phenomenon, the great difficulty was to exclude 
the influence of temperature. An adiathermanous magnetizing apparatus 
was made by winding the copper on a wide glass tube, into which a caout- 
chouc tube was introduced, with a smaller glass tube within it; the wire itself 
being wrapped in paper. 
Special arrangements were made also to reduce the intensity of (4) the 
extra current. 
These due precautions having been observed, a large transient diminution 
of resistance, and a smaller permanent diminution, were observed, the former 
amounting to 2 per cent. 
A. New Form of Spectrometer — is described by Dr. J. W. Draper, differing 
from the ordinary spectroscope, in the fact that whereas that deals with wave- 
