[ 5° 8 ] 
Improper Quantity is that which cannot bemeafured 
by its own Kind 5 but to which we aflign a Mcafure 
by the means of fome proper Quantity that is related 
to it. Thus Velocity of Motion, when we confider 
it by itfelf, cannot be mcafured. We may perceive 
one Body to move fader, another (lower ; but we 
can have no diftind Idea of a Proportion or Ratio 
between their Velocities,, without taking in lome 
Quantity of another Kind to meafurc them by. 
Having therefore oblervcd, that by a greater V elocity 
a greater Space is palled over in the fame time, by 
a lefs Velocity a lefs Space, and by an equal Velo- 
city an equal Space,- we hence learn to meafure 
Velocity by the Space faffed over in a given Time, 
and to reckon it to be in exact Proportion to that 
Space : And having once affigned this Meafure to it, 
we can then, and not till then, conceive one Velo- 
city to be exactly double, or half, or in any other Pro- 
portion to another 3 we may then introduce it into 
mathematical Reafoning without Danger of Confu- 
fon, or Error, and may alfo ufe it as a Meafurc of 
other Improper Quantities. 
All the Kinds of Proper Quantity we know, may, 
I think, be reduced to thefe four, Extenfion, Du- 
ration, Number, and Proportion. Tho’ Proportion 
be meafurable in its own Nature, and therefore 
hath Proper Quantity, yet as Things cannot have 
Proportion which have not Quantity of fome other 
Kind, it follows, that whatever has Quantity mud 
have it in one or other of thefe three Kinds, Ex- 
tenfion, Duration, or Number. Thefe are the Mea- 
fures of themfelvcs, and of all Things elfe that are 
meafurable. 
Number 
