160 REPORT—1896. 
latter course might readily lead to confusion, and would necessitate the 
retention of the constant factor J=4:2x107 in our equations whenever 
they involved electrical or mechanical measurements. 
To put the question in a brief and concrete form for the consideration 
of the Committee, I think that the views above expressed might be 
embodied in some such resolutions as the following :— 
1. That the thermal equivalents of the practical units of electrical 
energy above mentioned may be taken as convenient absolute units of 
heat. 
2. That when used to denote quantities of heat these units may be 
distinguished, if necessary, by prefixing the word ‘ thermal.’ 
3. That the ‘thermal watt-second,’ which is intended to represent 
10’ c.g.s. units of energy, be also called a ‘Joule.’ 
4. That the heat developed by an electromotive force equal to that of 
a standard Clark cell at 15° C., when acting through a resistance equal to 
one standard ohm, may be taken as 1-4340 Joule per second. 
5. That (pending the results of further investigations) the quantity of 
heat required to raise the temperature of one gramme of water through 
one degree of the centigrade air thermometer in the neighbourhood of 
10° C. may be taken as 4-200 Joules. 
6. That the thermal watt-hour, which is equal to 3-600 Joules, may 
be taken as equal to $ths of the kilogramme degree centigrade at 10° C., or 
as equal to 3:4 times the pound degree Fahrenheit at 50° F. 
7. That for the reduction of observations to the standard temperature 
of 10° C. or 50° F., the temperature coefficient of the diminution of the 
specific heat of water may be taken as -00036 per 1° C., or -00020 per 
1° F., over the range 10° to 20°. 
With regard to the last resolution I do not see that anything would be 
gained in the present state of our knowledge by adopting a more compli- 
cated or discontinuous formula of reduction, until we are prepared to 
extend it to higher ranges of temperature. 
The name ‘Joule,’as that of the father of the mechanical measurement 
of heat, would not, I think, be open to objection. At the same time I feel 
that the choice of a special name for the absolute unit of heat is one com- 
paratively of secondary importance. The really essential points to impress 
upon the world of science in general, and upon engineers in particular, 
are, that the specific heat of water is far from constant, and that 772 
foot-pounds are not very accurately equivalent to the B.T.U. Also that 
in measuring quantities of heat by the rise in temperature of a mass of 
water it is most important to have an accurately verified thermometer, 
and to state the limits of temperature between which the observations 
were taken. It would certainly be a great advantage for the reduction 
and comparison of observations to use always the same standard formule, 
such as those which you suggest ; but it would still be necessary in accurate 
work to state the limits of temperature for subsequent identification, should 
these formule prove on more exact investigation to be not sufficiently 
approximate. 
