236 DR. A. A. RAMBAUT ON UNDERGROUND TEMPERATURE AT OXFORD 
grass about 5 feet long by 4 feet wide. One edge of the pit coincided with the 
edge of the grass plot, and the corresponding side of the pit was made as nearly 
vertical as possible. Into this vertical face four iron tubes were driven horizontally, 
the tubes being formed with spikes at their ends to facilitate this operation. The 
tubes are 4 feet long, and into them the thermometers were inserted with the leads 
attached, the mouths of the tubes were sealed up with tow and red lead, and the pit 
filled in. 
The first four thermometers were placed at depths of (approximately) 6 inches, 
1 foot 6 inches, 3 feet 6 inches, and 6 feet respectively ; but Mr. Stone soon saw the 
advisability of placing another at a lower level, and intended to have gone to a 
depth of 20 feet. But as water was met with at a depth of 10 feet 6 inches, he 
decided to place it just above the water level, at a depth of 10 feet. 
This thermometer was buried, not directly under the four earlier ones, but in a 
separate pit at the other side of the Stevenson screen. This was apparently done 
to avoid disturbing the leads of the thermometers which were already in position, 
but it would have been rather more satisfactory if all had been placed in the same 
vertical plane. 
It is also, perhaps, to be regretted that one or two similar thermometers were not 
buried to considerably greater depths. The presence of water, however, complicated 
matters and introduced conditions different from those which prevailed in the dry 
gravel above. It is not, for example, to be supposed that the thermal conductivity 
or the diffusivity of permanently water-logged gravel would be the same as that of 
the drier material above it. Hence it would appear necessary to put at least two 
thermometers below the permanent water-level in order to study the flow of heat 
under such circumstances. Besides, it is highly probable that the gravel stratum 
is not very much thicker than 10 feet. Excavations in the neighbourhood show that 
the blue Oxford clay is likely to be met with at any depth 'below 12 feet from the 
surface, and in this, of course, the thermal conditions would be likely to prove wholly 
different from those in the gravel. 
The actual depths of the various thermometers as measured in October, 1898 
(when the pits were standing open to enable us to re-standardise the thermometers) 
were as follows : — 
Thermometer .1 2 3 4 5 
Depth . . . 64 in. 1ft. 6 in. 3 ft. 6g in. 5 ft. 84 in. 9 ft. 11^ in. 
These thermometers, with the Callendar and Griffiths resistance box, which 
could be connected with each thermometer through a switchboard, had been set up 
as I have stated, shortly before Mr. Stone’s death. 
On my appointment to the post of Radcliffe Observer, I took an early opportunity 
of examining the apparatus, and partly with a view of familiarising myself with all 
its details, I proceeded to determine the comparative values of the coils, and to 
