ON DIRECT PROBABILITIES. 31 



for the thing itself: thus we talk of a temperature of 

 60, when, in fact, each 1 only means a certain length 

 on the tube of the thermometer. It will illustrate this 

 to take a case in which we do not confound the thing 

 and its measure; in the barometer, for instance, we 

 never say that the air's weight is 30 inches, but that the 

 height of the barometer is 30 inches. 



The technical words, probability and improbability, 

 must now be considered as meaning the same thing in 

 different degrees. If there be only one white ball out 

 of a thousand, we usually say that to draw the white 

 ball is possible, but not probable. We now speak of it 

 as having a small probability, namely TO^T) ', we might 

 say it has a great improbability, namely -f-^^j but this 

 phrase is not customary. The moment we obtain either 

 numerical measures, or distinctions which are not verbal, 

 the distinctions which are verbal frequently become su- 

 perfluous and inconvenient. Thus in the art of book- 

 keeping, profit and loss never appear as separate words, 

 but only as part of a complex term prqfit-and-loss, 

 meaning, one or the other, according to the side of the 

 account on which the item is found. To a mercantile 

 reader, we should say that probability means probability- 

 and-improbability the first or second, according as its 

 measure is greater or less than -J-. When the number 

 of favourable and unfavourable cases is the same, say 50 

 of each, the probability of the event is T 5 ^ or \ ; and in 

 this case we say in common life that there is a balance 

 of probabilities, or that the event has an even chance. 



By the word chance with the article (a chance) we 

 mean one single way in which an event may happen, as 

 when we say that every white ball adds a chance to the 

 prospect of drawing a white ball. In the first instance 

 above, the chances of white and black are as 20 to 27. 

 It is also usual to say that the odds are here 27 to 20 in 

 favour of black against white. 



Questions on probability are twofold in character : 

 1 , Where we know the previous circumstances and re- 

 quire the probability of an event. 2. Where we know 



