[ 387 ] 



XI. Observations on the Anomalous Behaviour of Delicate Balances, and an 

 Account of Devices for Increasing Accuracy in Weighings. 



By J. J. MANLEY, Hon. M.A. Oxon., Daiibeny Curator, Magdalen College, Oxford. 



Communicated by Prof. E. B. ELLIOTT, F.R.S. 



(Received June 21, Read November 10, 1910.) 



CONTENTS. 



Page 



Introductory 387 



Preliminary observations and methods 389 



Conditions under which final experiments were conducted 392 



Some experiments with a balance having a circular beam 392 



Possible causes of observed irregularities 394 



Of side-slip 394 



Of flexure 



(a) General effects of flexure 395 



(b) Nature and degree of flexure 395 



(c) Differential flexure 396 



Of lateral displacement of a knife-edge 398 



Effects produced by variations in the temperature of the beam 400 



Variations in the temperature within the balance case 



(a) The differential bolometer 403 



(b) Experiments with the differential bolometer 405 



Method for maintaining the air near the beam at uniform temperature 407 



The minor undulations in a resting-point curve 410 



The major undulations in a resting-point curve 411 



Tests showing efficacy of the precautions advocated 412 



Summary 415 



Introductory. 



IN this communication it is desired to draw attention to certain difficulties which 

 were encountered during the standardization of a set of weights, and to show how 

 they were investigated and overcome. 



The weights were compared by the combined methods of vibration and reversal, 

 the sensibility of the balance being determined for each particular load either 



VOL. COX. A 469. 3 D 2 4.11.10 



