ANOMALOUS BEHAVIOUR OF DELICATE BALANCES, ETC. 



401 



displacement of the II. P. with increase in temperature. It was accordingly decided 

 to investigate this point more fully, and for this purpose the following method of 

 procedure was adopted. 



14 16 



ia 



20 



The beam was first thoroughly fatigued with the load which it was desired to use 

 in the experiment, and so reduced to a normal condition. When the temperature 

 within the balance case was found to be constant, observations were made for the 

 determination of the R.P. for that particular temperature. The room was then 

 warmed about 2 C., and as soon as the temperature had again become constant, the 

 R.P. was re-determined. Proceeding in this manner, the Pt.P. was measured over a 

 range of 5 or 6 C. Finally, the room was cooled down to approximately the initial 

 temperature, and the first set of observations repeated. 



This last constitutes a very necessary precaution, for it may happen that appreciable 

 particles of dust may find their way more freely to one pan than to the other ; the 

 real values for the R.P. would, as a consequence, be more or less masked. If the two 

 sets of observations effected at the lowest temperature were in close agreement, we 

 felt justified in accepting the whole series. Upon one or two occasions only was it 

 found necessary to discard a series owing to a want of agreement between the first 

 and last experiments. 



Using the Gallenkamp balance, experiments were made with three different loads : 

 (a) with pans alone, (b) pans+100 gr., and (c) pans + 200 gr., the last named being 

 the maximum load for which the instrument was built. The results obtained are 

 plotted so that the curves show the apparent increase in the value of one of the loads 

 relatively to the other. 



The resultant graphs (Fig. VI.) reveal three important points : (a) for any given 

 load the R.P. can only be constant when the temperature is invariable ; (b) the 

 displacement of the R.P., due to a given alteration in the temperature,' increases 

 with the load ; (c) for this particular balance, the curve representing the changes 



VOL. cox. A. 3 F 



