G. H. KNIBBS. XXXVII. 
Professor King’s experiments of flow through a series of 
discs of wire gauge shewed some departure from the 
Poiseuille law expressed in equation (2), and similarly 
through discs of perforated brass, and through sandstone. 
F. H. Newell’s experiments of the flow of water and of oil 
through rock also shew some departure. Flow through 
Italian marble on the other hand shewed good agreement, 
the porosity being no doubt very small. 
Investigations have been made by Seelheim,’ by Welitsch- 
kowsky* and Wollny,’ the former shewing very good agree- 
ment with the Poiseuille law. 
King experimentally examined the effect of coarseness 
of grain on rate of flow, the results led to a theoretical 
investigation by Professor OC. 8. Slichter, whose fine mono- 
graph on the motion of ground waters leaves little to be 
desired.* 
d. Theoretical investigation.—lIf four spheres be placed 
in contact in different ways ona plane, the angles between 
the lines joining the centres will range between 60°, 120°; 
to 90°, 90°. The small angle may be called 9, see Figs. 2 
and 3, the former denoting the minimum interstitial area, 
the latter the maximum, and the area being 
Fig. 2. Sum of two shaded areas=r? (2v3 —7)=0°32251 r? 
Fig. 3. Shaded area = r* (4 — 7) = 0°85841 r’ 
A little consideration will shew that whether spheres 
are packed like Fig. 2 or Fig. 3, another sphere being on A 
in either, the result is absolutely the same: the figures 
represent two views of the closest system of packing. 
* Methoden zur Bestimmung der Durchlissigkeit des Bodens, Zeit. f. 
analyt. Chem. x1x., p. 387. 
” Archiv. f. Hygiene, 11., 499 —512, 1884. 
3 Forschungen auf dem Gebiete der Agricultur-Physik. xiv., pp. 1 — 28, 
1891. 
* Theoretical investigation of the motion of ground waters—U. S. 
Geolog. Survey, Report 1897-8, pp. 295 — 384. 
