XXI. 
THE PERCOLATION OF RAIN THROUGH COMPARATIVELY LIGHT 
AND THROUGH COMPARATIVELY HEAVY SOIL. 
By Edward Mawley, E.E.Met.Soc., F.B.H.S. 
Read at Watford, 13 th April, 1891. 
Before considering the observations themselves it may not be 
out of place if I preface this modest enquiry with a brief history 
and description of the percolation-gauges with which they were 
made. 
About ten years ago, when residing at Croydon, I was desirous 
of testing for horticultural purposes the effect of mulching upon 
the moisture and temperature of the ground. I consulted my 
friend Mr. Baldwin Latham, M.Inst.C.E., also a resident in 
Croydon, and well known as a leading authority on all matters 
relating to underground-water, and he advised me to employ for 
this purpose percolation-gauges similar to those he had then in use in 
his own garden. Acting upon Mr. Latham’s suggestion I had 
made two open slate cisterns, each three feet square and three feet 
deep. These were sunk into the ground to within a few inches of 
their upper edges, and in the centre of the bottom of each cistern 
was inserted a pipe which led into a small covered chamber at the 
side. Over the bottoms of these cisterns I placed a layer of pebbles, 
and over these some gravel, the two layers taken together being 
three inches deep. The cisterns were then filled up with ordinary 
garden soil to the depth of thirty inches, or to within three inches 
of the top of them. The stones and gravel were introduced beneath 
the soil with a view to equalise the drainage over the whole area 
of each of these percolation-gauges, for such they had now become. 
In the chamber at the side under the ends of the conducting-pipes 
were placed cans capable of holding several gallons of water apiece, 
to receive the drainage from the gauges. In the centre of each 
gauge was inserted one of Symons’ earth-thermometers, with its 
bulb at the depth of one foot below the surface of the soil. 
I was so much pleased with the working of these gauges that 
when I removed to Berkhamsted, about six years ago, I brought 
them with me and had them sunk side by side in my present 
garden in a line with my rain-gauges and other meteorological 
instruments. The mulching experiments having been completed, 
I thought that it would be interesting to employ them here as 
permanent percolation-gauges. One of the gauges was accordingly 
filled with some of the lightest soil, and the other with some 
of the heaviest soil obtainable in the neighbourhood. In all other 
respects, however, the arrangements are precisely the same as those 
I have described as having been used for the experiments at 
Croydon. The light soil is composed chiefly of disintegrated clay, 
vegetable earth, and numerous flints; while the heavy soil is mostly 
a stiff yellow clay with an equally liberal addition of flints. Both 
are natural soils and were placed in the gauges as nearly as 
