38 Arrangement and Formation of the Series. [CHAP. n. 



these assumptions, and therefore something resembling the 

 consequences which follow from them, is really secured in a 

 very great number of cases. But although this may prevail 

 approximately, it is in the highest degree improbable that it 

 could ever be secured, even artificially, with anything ap 

 proaching to rigid accuracy. For one thing, the causes of 

 deflection will seldom or never be really independent of one 

 another. Some of them will generally be of a kind such that 

 the supposition that several are swaying in one direction, 

 may affect the capacity of each to produce that full effect 

 which it would have been capable of if it had been left to do 

 its work alone. In the common example, for instance, of 

 firing at a mark, so long as we consider the case of the toler 

 ably good shots the effect of the wind (one of the causes of 

 error) will be approximately the same whatever may be the 

 precise direction of the bullet. But when a shot is consider 

 ably wide of the mark the wind can no longer be regarded as 

 acting at right angles to the line of flight, and its effect in 

 consequence will not be precisely the same as before. In 

 other words, the causes here are not strictly independent, as 

 they were assumed to be ; and consequently the results to be 

 attributed to each are not absolutely uninfluenced by those 

 of the others. Doubtless the effect is trifling here, but I 

 apprehend that if we were carefully to scrutinize the modes j 

 in which the several elements of the total cause conspire i 

 together, we should find that the assumption of absolute 

 independence was hazardous, not to say unwarrantable, in a 

 very great number of cases. These brief remarks upon the I 

 process by which the deflections are brought about must) 

 suffice for the present purpose, as the subject will receive a 

 fuller investigation in the course of the next chapter. 



According, therefore, to the best consideration which 

 can at the present stage be afforded to this subject, we may 



