•28 MR. L. F. RICHARDSON: MEASUREMENTS OF ATMOSPHERIC TURBULENCE. 
X. Summary. 
Part I. deals with notation. Measures of turbulence may advantageously be 
expressed in the form £ in 
** =*(*&) 
a t dpVdp/' 
where p is the pressure (here used as a measure of height), t the time, and x may 
be horizontal velocity in a fixed azimuth, or potential temperature, or water per 
mass of atmosphere. It is suggested that £ might he called the “ turbulivity.” Its 
dimensions are grm. 2 cm. -2 sec. -5 . Better still is the conductivity c = £p~ l g~ 2 . 
In Part II. the eddy-shearing stress on the ground is deduced from pilot balloon 
observations. Values on land in any self-consistent dynamical units are found to 
range from 0'0007 to 0'007 times the value of m 2 /p, where m is the mean momentum 
per volume up to a height of 2 km. and p is the density. Compare G. I. Taylor, 
‘ Roy. Soc. Proc.,’ A, vol. 92. 
In Part III. evidence is given to show that the eddy-viscosity across the wind at 
Liridenberg increases with height, and, except near the ground, is much greater than 
the eddy-viscosity along the wind. Here £ ranges from 10 4 to 5 x 10 5 . 
In Part IV. the spreading of a lamina of smoke is considered. Values of £ ranging 
from 7 to 140,000 are found. £ increases both with height and with velocity. 
In Part V. the derivation of ^ from smoke observations is examined more 
thoroughly. 
Part VI. deals with Osborne Reynolds’ eddy-stresses. For one occasion an 
attempt was made to measure simultaneously all six components of stress by 
observing the motion of thistledown. The three direct stresses are easily measured. 
Not so the shearing stresses however, one was found to be 2'4 times its probable 
error. 
Part VII. summarizes the theory of scattering of particles. 
Part VIII. contains numerical values derived from scattering. 
In Part IX. the turbulivity £ is estimated from the rising of cumuli in calm 
weather and found to be 10' 5 , applicable only in the sense of friction. Thus the 
whole range of £ observed in the free atmosphere was from 7 to a million in 
contrast with 0’2 in perfectly still air in a laboratory. The eddy-stresses observed 
have ranged in absolute value from 0'004 to 110 dynes cm. -2 . 
