INTRODUCTION. 
stand at the other extremity of the scale. Theirs are the 
sciences in which experiment has been brought to its greatest 
perfection. But even so, statistical methods still find application. 
In the first place, the methods available for eliminating the effect 
of disturbing circumstances, though continually improved, are not, 
and cannot be, absolutely perfect. The observer himself, as well 
as the observing instrument, is a source of error; the effects of 
changes of temperature, or of moisture, of pressure, draughts, vibra- 
tion, cannot be completely eliminated. Further, in the problems 
of molecular physics, referred to in the last sentences of § 6, 
multiplicity of causes is of the essence of the case. The motion 
of an atom or of a molecule in the middle of a swarm is dependent 
on that of every other atom or molecule in the swarm. 
10. In the light of this discussion, we may accordingly give the 
following definitions :— 
By statistics we mean quantitative data affected to a marked 
extent by a multiplicity of causes. 
By statistical methods we mean methods specially adapted to 
the elucidation of quantitative data affected by a multiplicity of 
causes. 
| By theory of statistics we mean the exposition of statistical 
methods. 
The insertion in the first definition of some such words as “to 
a marked extent ” is necessary, since the term ‘statistics ” is not 
usually applied to data, like those of the physicist, which are 
affected only by a relatively small residuum of disturbing causes. 
At the same time, ‘statistical methods” are applicable to all such 
cases, whether the influence of many causes be large or not. 
REFERENCES. 
The History of the Words “Statistics,” “ Statistical” 
(1) Joun, V., Der Name Statistik ; Weiss, Berne, 1883. A translation in 
Jour. Roy. Stat. Soc. for same year. 
(2) YuLg, G. U., ““ The Introduction of the Words ‘Statistics,’ ¢ Statistical,’ 
inte $us English Language,” Jour. Roy. Stat. Soc., vol. lxviii., 1905, 
p. 391. 
The History of Statistics in General. 
(3) Jomx, V., Geschichte der Statistik, 1%¢ Teil, bis auf Quetelet; Enke, 
Stuttgart, 1884. (All published ; the author died in 1900. By far the 
best history of statistics down to the early years of the nineteenth 
century.) 
(4) MonL, ROBERT VON, Geschichte und Litteratur der Staatswissenschaflen, 
3 vols. ; Enke, Erlangen, 1855-58. (For history of statistics see 
principally latter half of vol. iii.) 
A