442 
MR. E. H. GRIFFITHS OH THE VALUE OF 
a rising thermometer, for “ sticking ” is far less likely to occur when the mercury is 
advancino; than when receding^. 
We have found that all observations of slowly falling temperatures (when taken 
with a mercury thermometer) are unsatisfactory for the above reason. Again, the 
conditions resemble more nearly, in every respect, those prevalent during a “ J ” 
experiment. On this account, we did not desire to reduce the “ stirring heat,” even if 
we had been able to do so, since the loss, due to radiation, &c., would, at the higher 
portions of the range, have mastered the stirring supply, and the observations would 
have had to be taken on a falling thermometer, a mode of observation which, guided 
by the results obtained in previous years, we had decided to reject. 
It appeared unlikely that Newton’s Law of Radiation would hold over our range, 
and we anticipated a decided curvature in the line showing our ‘‘ non-electrical 
supply.” 
We first proceeded to determine Isolated points on this curve (ordinate = rise 
in temperature per second, abscissa = difference in temperature betw^een the calori¬ 
meter and the outside temperature), but these appeared to fall so nearly on a straight 
line, that we decided to follow its course over our range of temperature, using a small 
mass of water so that the chang-es in the value of the rise should be as marked 
as possible. A very large number of experiments wmre made in order to decide this 
point—for, if the exponential formula given by Dulong and Petit holds, the curvature 
ought to have been marked. Although changes in the specific heat of water and of 
the calorimeter would influence the inclination of the line, it appeared unlikely that 
they would affect it in such a manner as to straighten it ; and further, the effect 
of such changes would alter as the mass of water changed.* 
The numbers alone resulting from these observations half fill a large note-book, and 
to give them in full would occupy too much space. As an example, we venture to 
give experiments 51 to 54, exactly as they appeared in our notes. As the method 
employed never varied, we will, in other cases, simply give results, and we select this 
series because it was the first done by us with the object of tracing the “non-electrical 
supply ” curve throughout the greater part of our range. 
The numbers in the columns marked “ time,” are those given by the chronograph 
tape. New tapes were used after the readings at 343, 407, and 458, and the times of 
rising between these temperatures Avere not noted ; therefore, the experiments at those 
ranges are numbered as separate experiments although taken consecutively. 
No temperatures were taken whose readings ended in 0 or 5 because, as these were 
* We may state at once that (although some slight signs of cni’Tature are visible ■when the mass of 
water is great) by assiiming the non-electrical supply to be a linear function of the temperature (when 
the rate of stirring is constant), we introduce no error snfBcient to affect our results, and this con¬ 
clusion is based on the data supplied bjr more than 100 “ stirring and radiation” experiments. If the 
results were expressed in terms of the mercury thermometer scale, the curvature would, of course, be 
marked. 
