NINTH ORDINARY MEETING. 85 



The units encountered in electrical science are the most complex 

 of all ; and the labours of scientific men in overcoming them have 

 had an indirect effect in advancing the methods of elementary calcu- 

 lation. It is, however, only the notation for the principal units P 

 and Q in terms of L, M, T that is complex. Given P and Q the 

 notation for the remaining units is simple enough. Of the two 

 units of electric quantity the notation for the electi'ostatic unit is 

 the same as that for the unit of magnetic pole, while the notation 

 for the electromagnetic unit involves that for the magnetic pole. 



General symbols for a unit such as M and Y are of great service 

 in elementary calculations apart from the use in a notation for 

 derived units. The chemist is always using the phrases ' part by 

 weight,' and 'part by volume;' these ideas are expressed by M 

 and Y. 



NOTATION FOR GENERAL UNITS. 

 I. — Geometrical. 



Quantity. Notation. Dimensions. 



Length L 1 



Surface L by L, S P 



Volume L by L by L, V P 



Angle L arc per L radius 1° 



Sine L opposite per L along P 



Curvature Radian per L 1~^ 



II. — Kinematical. 



Time T t 



Velocity L per T 1 1-^ 



Acceleration L per T per T 1 1~^ 



Angiilar Velocity L arc per L radius per T t"^ 



III. — Dynamical. 



Mass M m 



Density M per V m 1-* 



Mass-vector M by L ml 



Momentum M by L per T ml t-^ 



Force M by L per T per T, F ml t-^ 



Pressure F per S m 1~"^ t— ^ 



Work M by L per T per T by L, W m P t-^ 



Activity W per T m 1'^ t~' 



IV. — Thermal. 



Temperature O d 



Heat M of water by 9, H m ^ 



Thermal capacity M of water by 9 per M d 



