AS DETERMINED BY FIVE PLATINUM-RESISTANCE THERMOMETERS. 
255 
Values of x/tt/k deduced from the Half-yearly Wave. 
Thermometers 
From diminution 
From retardation 
compared. 
of amplitude. 
of phase. 
No. 5 and No. 4 
04445 
04236 
!) ^ J, 3 
4393 
4187 
Ft O 
33 ^33 3 3 ^ 
4306 
4129 
>> 4 ,, )> 3 
4287 
4092 
>) 4 ,, ,, 2 
4164 
4022 
9 9 
33 ° 33 3 3 ^ 
4033 
•0949 
Means . . . 
04271 
04102 
Mean of both , . . 04187 
I have omitted the results derived from the readings of No. 1, as they seem too 
much affected by short period variations to afford reliable results. This thermo¬ 
meter, too, is buried, in a surface soil which is of quite a different character from 
the sandy gravel containing the other thermometers. 
The values of x/tt/k deduced from the annual wave are, of course, much more 
trustworthy than those obtained from the half-yearly wave, and the larger discrep¬ 
ancies in the individual results from the latter are not surprising. It is, however^ 
satisfactory to note how these corroborate the others, showing, for instance, larger 
values resulting from the comparison of Nos. 5 and 4 than from that of any other 
pair. This may possibly be due to a smaller value of k for the stratum of gravel about 
4 feet thick which separates these two thermometers, than for the higher strata, or 
to the fact of No. 5 being buried at some distance (9 feet 6 inches) from the vertical 
plane containing the other three. 
Unfortunately, when the pits were open, no very critical examination of the 
character of the gravels at different depths was made ; but it is proposed to repair 
this omission when next the thermometers are dug up. 
The excessively close agreement of the mean values of \/ tt/k derived from the 
annual and half-yearly waves is very remarkable (especially in view of the fact that 
the results are deduced from the observations of a single year), and seems to indicate 
a high degree of precision in the observations. 
The systematically larger values found from the diminution of amplitude, as com¬ 
pared with those deduced from the retardation of phase must be traced to some 
other cause, and may possibly be due to the proximity of the Observatory building, 
the south front of which is situated at a distance of 36 feet from the thermometers. 
The temperature of the ground beneath the buildings would in all probability be 
different from that at an equal depth beneath the exposed surface. There would, 
