480 TRANSACTIONS OP SECTION 6. 



Finally a method of calculating the open circuit characteristic of a single- 

 phase motor was given. The applied pressure was assumed to be sinusoidal, 

 and the effect of saturation on the shape of the current wave was taken into 

 account. 



4. Some Preliminary Notes on a Study as to Human Susceptibility to 

 Vibration. By W. Pollard Digby and Captain Sankey. 



The authors pointed out that the variation of individual human sensitiveness 

 has been investigated in regard to senses of taste, sight, sound, and weight; and 

 remarked that the phenomenon of the fact that different persons are affected in 

 different manners by the same conditions of vibration calls for investigation. 

 The phrase ' human susceptibility to vibration ' was coined to cover the range 

 of sensitiveness of various people to vibrations of short duration of different 

 amplitude and frequency, together with their opinions as to when these vibrations 

 approached or exceeded the point of being a nuisance. 



The authors have employed both verbal standards of degree of vibration and 

 precise unit of measurement. The former ranges from 1 to 8 degrees, 

 imperceptible vibrations being classed as 1, and perceptible vibrations consti- 

 tuting an excessive nuisance as 8. The precise unit of measurement is that 

 of a vibration having a maximum linear amplitude of ith millimeter at a fre- 

 quency of 10 cycle per second. From their investigations, so far confined to only 

 a limited number of cases, the authors deduce that : — 



(1) The range of vibration classed as imperceptible is a wide one. Generally 

 vibrations having an intensity of O'lO to 0"20 unit are imperceptible, but are in 

 a lesser number of cases classed as faintly or very faintly perceptible. 



(2) In regard to very faintly perceptible vibrations, three persons classed this 

 as under 010 unit, six as between O'lO and 0'20, six as between 0'40 and 0-50, 

 while seven persons could only distinguish vibrations in excess of 0'50 unit. 



(3) All individuals show a fatigue effect and lose their sense of discrimination 

 after thirty or forty minutes. Generally the sensitiveness is diminished. 



(4) Individuals are divisible into two broad classes. Those capable of dis- 

 crimination of vibrations of small intensity do not give consistent opinions as 

 to vibrations of large intensity. The opposite effect is observed in those capable 

 of classifying vibrations of larger intensity. 



(5) So far the general consensus of opinion points to conditions of per- 

 ceptible vibration just attaining a nuisance being reached for a mean intensity 

 of one unit. Persons of delicate intensity rate this in the neighbourhood of 0'70 

 unit, and persons of coarse perceptiveness at about two units. 



The authors suggested that it will be of interest to ascertain the effect of 

 variations of conditions of physical health, age, sex, and occupation in this 

 respect. 



They concluded by asking for the co-operation of members of the British 

 Association by their acting as subjects for experiment, and urge that from many 

 points of view, not least the legal one, there should be some definition of what 

 exact intensity of vibration constitutes a nuisance. Assistance in the further re- 

 search contemplated by the authors will only involve spending about forty-five 

 minutes in Westminster, during which time the visitor's hand is placed on a 

 table and the opinions are expressed of the vibration of the table, whether im- 

 perceptible, just perceptible, or a nuisance. 



5. Interim Report on Gaseous Explosions. — See Reports, p. 130. 



6. The Electrical Conductivity of Light Aluminium Alloys. 

 By Professor Ernest Wilson. 



The last report on the exposure tests of a certain series of light aluminium 

 alloys was made in 1908. ' The present paper includes tests made in July 1911. 



1 See Brit. Assoc. Reports, 1908. 



