150 
DR. H. T. BARNES ON THE CAPACITY FOR HEAT OF WATER 
of the mechanical equivalent, but also the variation of the thermal unit over a 
limited range. More recently we have the exceedingly careful experiments of 
Miculescu, of Griffiths, of Schuster and Gannon, and of Reynolds and Moorby. 
It is evident from only a cursory glance at the work of these and the host of other 
investigators, that the science of calorimetry must he regarded as incomplete and 
approximate so long as its fundamental unit remains in doubt. To obtain, as is 
urgently needed, a complete series of determinations of the capacity for heat of water 
over the entire range of temperature is manifestly impossible by the older methods of 
calorimetry. A new method has long been required, more completely free from the 
influence of extraneous surrounding conditions. 
During a conversation which I had with Professor Callendar, in the autumn 
of 1896, we discussed the unsatisfactory state of our knowledge of the specific heats 
of water and mercury. Professor Callendar pointed out that what was required 
was a new method of calorimetry, which would reduce to a minimum many of the 
larger corrections inherent in, and making uncertain, the older methods. Such he 
considered possible in a continuous, or steady, flow method, in which a stream 
of liquid could be made to continuously carry oil' a definite and measurable supply of 
heat. This method he considered capable of great accuracy and free from nearly 
all the errors in the older methods. I very gladly consented to assist Professor 
Callendar in developing this method, which we commenced as a joint work early 
in 1897.* 
The early experiments with mercury will be discussed in full in another paper, and 
cannot be more than mentioned in this place. They were satisfactory in many 
respects, but must be considered more as preliminary attempts, the experience of 
which served so much to aid in later measurements with water. A calorimeter, 
designed for the determination of the specific heat of water, was set up and tested 
just previous to the meeting of the British Association at Toronto, to which body a 
preliminary note was sent describing the method in general terms. On the re-opening 
of the College session, in September of that year (1897), Professor Callendar was 
unfortunately obliged, through stress of work, to relinquish his connection as a joint 
observer in the experiments. My own duties, however, were such as to allow of a 
certain amount of time to be devoted to research, so that the work was carried on at 
intervals throughout the winter. During this session Mr. Russell W. Stovel, B.Sc., 
joined our graduate classes and devoted a large part of his time to assisting in the 
work. It is largely to his skill as an observer that it was possible to continue the 
work during this time. 
In the spring of 1898 Professor Callendar was called to London to fill the Quain 
Chair of Physics in University College, and was obliged to sever his connection 
entirely with the experiments. It was with extreme regret that we realized this, as 
* For theory of experiment and work done prior to 1897, see the paper liy Professor Callendar 
above, pp. 55-148. 
