HERTFORDSHIRE NATURAL HISTORY SOCIETY. 
lix 
one else had photographed. Hitherto no one had thought of photo¬ 
graphing snow-crystals on a large scale, or hoar-frost, so as to show 
their structure. He also referred to the deposit of lead from the 
smoke in the chimneys of smelting works, which resembles the 
incrustation of hoar-frost on wire netting, and the cause of which 
is unknown; and he said that the Society could help the British 
Association Committee on Geological Photography as well as that 
on Meteorological Photography, in both of which their President 
was interested. 
The lecture was illustrated by means of the oxy-hydrogen lantern, 
kindly lent by Mr. S. Monckton White, to whom the thanks of the 
Society were accorded. 
Ordinary Meeting, 13th April, 1891, at Watford. 
John Hopkinson, Esq., E.L.S., E.G.S., etc., President, in the 
Chair. 
Mr. Bichard Gibbs, Mr. Henry Lubbock, and Mr. T. Poster 
Woodman, were elected Members of the Society. 
Mr. Ernest Brunton, Erogmore House, St. Albans, and Dr. Henry 
Case, Medical Superintendent, Leavesden Asylum, Watford, were 
proposed for membership. 
The following papers were read :— 
1. “ The Percolation of Bain through comparatively Light 
and through comparatively Heavy Soil.” By Edward Mawley, 
E.B.Met.Soc., E.B.H.S. ( Transactions , Yol. VI, p. 175.) 
The President said that this was a most important question, 
and one of the observations he would make with regard to it was 
that the result of these experiments with the surface of the soil 
kept free from vegetation was very different from what the result 
would be if vegetation were growing on the surface. The experi¬ 
ments carried on at Hash Mills, at first by Mr. Dickinson and 
afterwards by Dr. John Evans, from the year 1840 up to 1884, 
showed that 46 per cent, of the rain falling on the surface 
percolated through three feet of the ordinary soil of the district, 
with grass growing on the surface, in the winter, and 4 per cent, 
only in the summer, showing a difference of 42 per cent., and an 
average of 25 per cent, per annum. That showed practically that 
if we had vegetation on the surface, we must depend upon the 
winter rainfall for our water-supply. Experiments made for 22 
years at Lea Bridge with gauges three feet deep, with grass growing 
on the surface, gave a percolation of 28 per cent, throughout the 
year. There, also, the percolation was very much greater in the 
winter than it was in the summer. The difference between these 
results and those arrived at by Mr. Mawley was evidently due to 
vegetation, so they could not at all consider that on an average 
anything like the amount which percolates through Mr. Mawley’s 
gauges gets to the underground water-level. It had been assumed 
