424 
MR. B. H. GRIFFITHS ON THE VALUE OF 
in columns 5, 9, 14, 18, and 22, Table XL., and the curve numbers in the succeeding 
columns. Further, this difference would recur in each experiment. No persistent 
discrepancy of any consequence is observable. In our own work we have expressed 
the value of these ranges to another figure, but we refrain from printing it until we 
produce more evidence. One possible cause of error in our total range yet remains, 
viz., the difference caused by unequal lag at the beginning and end of that range, and 
this difficulty cannot be surmounted by means of the same method as that used for 
determining the comparative values of the smaller ranges. 
Our experiments on this point were of the following nature :— 
A platinum thermometer E (Pt) of exceedingly small capacity for heat (the external 
diameter was only 3/16 inch) was placed in the calorimeter. The coil of this ther¬ 
mometer was pressed tightly against its glass envelope, which was of egg-shell thin¬ 
ness, and thus the thermometer was rendered extremely sensitive. Its stem passed 
down a condenser-tube, through which the tank water was continually drawn bv 
means of the water pump. The stem-resistance, therefore, remained constant, and 
thus only one observation was required, whereas with N three observations had to be 
taken to accurately determine a temperature. The value of II when the temperature 
of the calorimeter was steady was determined at the initial and final points of our 
range. The temperature was then lowered to our usual starting-point (10° C.), and 
raised in the same manner as during an experiment. The value of R was ascertained 
when the reading of (mercury thermometer) again indicated the initial and final 
points. No doubt the platinum thermometer also lagged, but we proved by inde¬ 
pendent experiments that it did so to an extremely small extent, and, if uniform, the 
lag was of no consequence, as it would only affect the elevation and not the range. 
Now in the platinum thermometer we have no “ sticking,” &c., and there is every 
probability that the lag is regular. The observer at the galvanometer called at the 
moment when the “ spot ” was seen to pass the zero point, the other observer taking 
the mercury readings at the same instant. This was done over four or five consecu¬ 
tive plugs, and the resistance deduced at the moment of passing the required points. 
The results indicated that the lag of the mercury thermometer was greater at the 
commencement than at the end of our range by (at our normal rate of rise) about 
0°'008 C.* The “ stationary range ” would, therefore, require diminishing by about 
•008 in 11° C., or by 1 in 1400. 
In order to investigate this point more fully another platinum thermometer (Q), 
having a naked wire, was placed in the calorimeter. The coil of this thermometer 
had fifty turns to the inch, and thus the different parts of the wire were very close 
together. The results were not satisfactory, the conduction across the water, under 
* The average lag of the mercury thermometer proved to be less than we anticipated. It, of course, 
depends, in a great measure, on the thoroughness of the stiri’ing; but when the mass of mercury that 
has to be heated is considered, the extreme lag, observed at our rate of rise, viz., •02'), is surprisingly 
small. 
