438 
MR. E. H. GRIFFITHS ON THE VALUE OF 
From the above results we drew the following conclusions :— 
(1.) That under the same conditions the quantity of heat developed was the same. 
(2.) That the work done increased slightly with the mass of water. 
(3.) That tr^ was a constant quantity.* 
If Nos. 1 and 3 were established, No. 2 was of little consequence, as we proposed 
to determine the heat developed for each mass of water. 
When it is remembered that our “ rate ” varied in the above experiments from 26 
to 34 revolutions per second, the close approximation of to a constant is remarkable, 
and, as we proposed to maintain a rate of, as nearly as possible, 30 revolutions per 
second throughout our experiments, it was evident that any assumption based on 
this conclusion, could lead to no appreciable error. Again, a considerable variation 
in the value of tr^ would have but little effect on the value of t, i.e, the time of 
rising 1° C. 
These experiments were regarded as only preliminary, and no special care was taken 
with regard to external temperature or pressure, and, it is probable, that many of the 
apparent discrepancies arose from such causes. Again, when the movement of the 
mercury column was so slow that from 50 to 100 seconds were taken in rising 1 miUim., 
it was difficult to estimate with great precision the time of apparent contact of the 
mercury column and the spider wire of the telescope. Personal errors of this 
description must, however, in the long run, tend to “mean out” and give a true average. 
Had we been able to bring our mechanical arrangements to such perfection that 
the rate of revolution was absolutely constant, it would have rendered the above 
investigation unnecessary, for the stirring correction would have been constant 
whenever the mass of water was the same. 
Although by the pressure regulator, described p. 378, the regularity of the motor 
was increased to an extent which those accustomed to the behaviour of these 
instruments hardly anticipated, we were unable to ignore the residual variations. It 
was, therefore, necessary to record the revolutions (the time per 1000 being taken in 
each case) throughout all our experiments. The labour, both of observing and 
calculating, was thereby greatly increased; but as we had no better means at our 
disposal, we had to submit to the inevitable. 
The establishment of the law that (with this stirrer) tr'^ might be regarded as 
constant, enabled us to apply with certainty the necessary corrections. 
As previously stated, our object was to deduce the rise in temperature per 1 second, 
at rate 30. If t is time of rise of 1° in any scale, then \jt — K'?*®, therefore, 
S. 1/^ = 3Kr^. Sr. Knowing l/ig (the rise per 1 second at any observed rate), and 
1/q (the rise at rate 30), we know 1/b — l/( 2 > is the term required to reduce the 
observation to the rate 30. 
The accuracy of the correction can be estimated by means of the above table. For 
* t = time rising 1° (in any scale), in seconds. 
r = rate of revolution, i.e., number of revolutions per second. 
