418 Nomenclature and Notation in Calorimetry 



g 100 C, but the difference between ioogC. and g 100 C. 

 is much less than the probable experimental error in any 

 calorimetric operation. In a table containing a column of 

 quantities of heat expressed in numbers of gramme-degrees- 

 Celsius, the nature of the unit would be indicated at the top 

 of the column by gC; exactly as, in a column of tempera- 

 tures, the unit is indicated by the symbol C. or F. The 

 original British heat unit is then clearly expressed by lb F. 



A heat unit made up of any unit of weight and any unit 

 of temperature can be perfectly expressed in this system. 

 Thus, if there were any advantage in doing so, we might have 

 g F., lb C., k R. and many others, and their meaning would 

 be at once apparent on inspection. 



In oceanographical work, where the heat exchanges be- 

 tween one layer of water and another, or between the water 

 and the air are under discussion, I have found the most 

 convenient heat unit to be the fathom-degree-Fahrenheit, 

 or the metre-degree-Celsius, which are abbreviated for the 

 purposes of notation into f F. and m C., respectively. The 

 nature of this unit will be most easily understood by con- 

 sidering an example. 



In a paper, ' On the Distribution of Temperature in Loch 

 Lomond in the Autumn of 1885,' read before the Royal 

 Society of Edinburgh, and published in its Proceedings for 

 the session 1885-86, I have given, at page 420, a table 

 of the changes in the distribution of heat in the direction of 

 depth, between several pairs of dates, in the Luss basin of 

 Loch Lomond. At a certain depth, indicated by the inter- 

 section of the temperature curves, the temperature of the 

 water is the same on both dates. The season being autumn, 

 the layer above this depth has been losing heat, partly to the 

 air above and partly to the water beneath, while the layer 

 below the depth of common temperature has been on the 

 whole a gainer. Thus, taking the dates September 5 and 

 October 15, the intersection of the temperature curves is 

 found at a depth of 16 fathoms; and in the interval of 

 forty days the mean temperature of the water above this 

 depth has fallen by 5'8 F., from 55'oF. to 49'2 F. The 



