452 Mr. E. H. Griffiths on 



therm, which is the exact equivalent of a " Rowland " could 

 be denoted by the phrase standard therm. 



Adopting the system of nomenclature above indicated I 

 venture to bring forward the following propositions for the 

 consideration of the Committee : — 



(I.) That 42 x 10 6 ergs be termed a " Rowland/'' 



(11.) That (pending the results of further investigations) 

 we assume that a therm at 10° is a standard 

 therm, i. e. the equivalent of a " Rowland/' 



(III.) In order to enable observers to express their results 

 in terms of a standard therm, we (pending the 

 results of further investigations) assume the validity 

 of the following expressions over the temperature 

 ranges indicated: — 



Kange 10° to 15°, 



Qio=-Q#{l--000415(«-10)}'; 



and over the range 15° to 20 c , 



Q 10 = Q,{ -99935 - -000284 (£- 10) } f. 



If this last suggestion was generally adopted we should be 

 able, when our knowledge of these changes became more 

 exact, to make the necessary corrections in the results of ob- 

 servations which had been reduced by these formulae. 



I have suggested the value 42 x 10 6 , since it is obviously 

 convenient to have as simple a number as possible, and the 

 adoption of this value would cause but little dislocation in 

 our existing system of measurements. True, this entails the 

 adoption of the somewhat low temperature 10° for the stan- 

 dard therm, but in order to secure a more convenient 

 temperature, say 15°, it would be necessary to replace 42 by 

 41*89 — a somewhat less convenient number. Further, the 

 close correspondence previously referred to between several 

 observers at 10° is an additional argument in favour of the 

 selection of the value above suggested. 



Of course propositions (II.) and (III.) would undergo 

 alteration as our knowledge became more accurate ; the 

 exact temperature at which a therm may be regarded as 

 the standard therm being ascertained by successive ap- 

 proximations. 



* The mean of the conclusions of Rowland and Bartoli and Stracciati 

 over this range. 



t The mean of the observations of Rowland, Bartoli and Stracciati, and 

 Griffiths over the range 15 c to 20°, the reduction from 15° to 10° being 

 made by the preceding expression. 



