DEVELOPMENT OF METEOROLOGY—ABBE. 303 
with balloons or kites to any given level in the atmosphere. These 
authors make the point that as the surface of the ocean is an equipo- 
tential surface, therefore observations reduced from it upward to 
some other equipotential surface of gravity possess simpler relations 
to each other than when reduced to a uniform height above sea level. 
With the help of the Carnegie Institution, Bjerknes and Sandstrom 
are now still further developing and improving their method with 
the assurance of throwing new light upon atmospheric motions. 
Even when we study the motions of gases on a small scale in our 
laboratories, we have the greatest difficulty in understanding the proc- 
esses that go on right before our eyes; still more is this the case with 
those that go on in the atmosphere. The smooth flow of air, like that 
of water, made visible by some fine floating particles, suddenly 
changes without apparent cause into a series of whirls and vortices, 
and then from whirls back to a steady, smooth flow. A vortex ring 
of air traverses a large room to a distance far greater than a fine 
straight jet can do, as though its large front surface experienced less 
resistance than that of a small jet. 
Under hydrodynamics proper I may mention the names of Chree, 
Bigelow, Bjerknes, J. J. Thomson, Ekholm, Margules, Wien, Shaw, 
and Rayleigh; also the discussion between Airy, Ferrel, Wien, and 
Kelvin as to the tides in the atmosphere, resting on the interpretation 
of a certain formula in the memoirs of Laplace, a subject that was 
finally elucidated by Doctor Ling, of Columbia University. Not only 
do we owe the mathematical theory of heat to Fourier and Poisson, 
but especially to the former a posthumous memoir on the motions of 
fluids in which the internal motions and the distribution of heat are 
mutually interdependent. This memoir is but a fragment, establish- 
ing certain differential equations, the solution of which is rarely pos- 
sible when the boundary conditions are given; so that in general we 
must at present rely upon partial solutions and suggestions derived 
from experiments or observation. To Rayleigh and Stokes we owe a 
number of memoirs on fluid resistances, including the first solutions of 
problems involving viscosity or internal friction of fluids. To Prof. 
Joseph Reynolds we owe some beautiful experiments showing how 
the motion of a fluid changes from a laminar flow to a vortical flow 
whenever the excess of internal energy amounts to a very small limit, 
and vice versa. 
To Willy Wien, a pupil of Helmholtz, we owe the development of 
problems relating to vortex and wave motions in the earth’s atmos- 
phere. To Professor Pockels, another pupil, we owe a very ingenious 
memoir on the influence of mountain slopes in forcing moist air to 
ascend and form clouds and rain. It is the presence of aqueous vapor 
in our air and the consequent thermodynamic complications that 
necessitates a combination of hydrodynamics with thermodynamics 
