100 Proceed ivgs of the Royal Society of Victoria. 



sets up considerable oscillations in the"^ galvanometer, and these 

 oscillations can only be due to a very considerable want of 

 uniformity of temperature in the contents of the receptacle, 

 while in themselves they make it very difficult to decide a.t what 

 instant a certain deflection of the galvanometer has been reached. 

 Two other causes further increase the risk of error : — in order to 

 admit the silver receptacle, the calorimeter must be opened and 

 this introduces errors due to radiation and convection chiefly 

 from the person of the operator, who must come close up to the 

 apparatus, and also allows of evaporation, and the amount of this 

 evaporation can hardly be determined by re-weighing as the 

 removal of the silver flask would carry away a certain amount of 

 water. 



Any one of these objections would in itself have been almost 

 suflicient to justify the rejection of the method, but all of these 

 sources of error had to be carefully avoided when the next 

 method was devised ; and though each is fairly obvious, it 

 required a good deal of experimenting to detect and localise it. 



The first step in the attempt to improve the method was in the 

 direction of avoiding temperature-eflects due to the proximity of 

 the observer to the apparatus, and the attempt was made to carry 

 out the manipulations by means of rods and pulleys worked from 

 a distance, the thermometers being read by telescope. This 

 succeeded in so far as to avoid the rapid fluctuations in the tem- 

 perature of the calorimeter just prior to immersing the silver 

 flask, but the difliculties with the thermal junctions still remained. 

 The introduction of a number of junctions into both vessels would 

 perhaps have given a nearer approach to a correct mean diflerence 

 of temperature, but the conduction of heat along the wires would 

 have introduced a corresponding disadvantage. 



Guided by the failures in this direction, a start was then made 

 on rather diflerent lines. The first trials of the new method were 

 made in a very primitive manner, in order to give some idea 

 whether it would be worth while to construct the proper 

 apparatus. A large cylindrical tin vessel of about ten litres 

 capacity had coiled in it several feet of lead-pipe — it was, in fact, 

 the condenser belonging to a still used in the laljoratory for 

 distilling water. This formed the calorimeter, and through the 

 pipe was run a stream of warm water so regulated as to flow in 



