422 
MR. E. H. GRIFFITHS OX THE VALDE OF 
and — '193 and — '300 as the differences, thus causing changes of '004 and '003, 
respectively, in our range, although causing differences of '010 and '008 in the 
elevation. 
Apart from errors of observation, we may, therefore, regard the limit of our range 
error as •003 in 11° C., i.e., 1 in 4000 ; and we believe it to be much less. 
As to experimental errors, it must be remembered that we have made the 
comparison of the platinum and mercury thermometers under the most favourable cir¬ 
cumstances. Both were immersed in the calorimeter, the cooling tube (Plate 2, fig. 2), 
having been removed to allow of the insertion of the platinum thermometer. The 
observer, with his eye at the telescope and his hand on the key could, by means of 
the current, set the temperature with extreme exactitude to any required reading E„, 
stirring being maintained at the same rate as during an experiment. Observations 
could thus be repeated at the same reading as often as necessary. 
Again, the observations taken by the observer at the galvanometer were enth’ely 
independent of the readings of the observer at the telescope, yet a difference of 
0°'004 C., on the repetition of an observation, was very unusual. 
Many hundreds of comparisons were made, the particulars of which we reserve for 
our second communication. 
We may mention that the comparisons made in 1892 differ from those of 1891 by 
'003 in range, but show a rise of about '010 in the actual elevation of E;,^. 
E,„ was one of three thermometers specially constructed for this work by Hicks. 
We set him a somewhat difficult task, as the dimensions of the bulb were strictly 
limited both in length and diameter, and the weight of mercury was also specified. 
The stem was divided into millimetres, about 40 millims. to 1° C., and the lower 
18 centims. were out of sight within the calorimeter tube, the graduation marked 0 
being within this tube and the 26th millimetre just appearing ahovm it. 
The reading 87'5 = 13°'990 C. ; the reading 537*5 = 25°'471 C. 
The graduations continued to 580 millims. 
Our method of observation obviated the necessity of attempting to divide the 
millimetres by eye. The thermometer was fixed in such a position that the view of 
the bore was unimpeded by any of the shorter graduations. When timmg changes 
of temperature the spider-wire of the telescope was placed on these graduations and 
the time of contact with the spider-wire observed. No attempt was made to take 
any reading terminating in 0 or 5, as these graduations extended across the bore and 
obscured the edge of the mercury column for about l/20th millim. Thus to obtain 
the time of passing a given point we were limited to the observation of four con¬ 
secutive transits, and for this reason, our “fixed points” were determined at 87'5, 
127'5, &c., and the time of passing these points deduced from the times at 86, 87, 
88, and 89, &c. 
A consideration of the behaviour of this thermometer (as well as of other narrow 
bore ones) rendered it evident that the ordinary method of calibration was insufficient 
