322 PERSONAL PREPARATION FOR RESEARCH. 



instance. In other cases where the effect is observable we 

 have not employed the correct method of observation. It 

 must also not be forgotten that, whilst making observa- 

 tions, we are very apt to be deceived by our senses ; a 

 large proportion of what we seem to observe, we do not 

 really observe, but infer. False observations, stated as 

 facts, are often more injurious to science than false 

 theories; the latter can usually be disproved, but the 

 former sometimes cannot, because the only opportunity 

 of doing so may have passed away. 



There are two general conditions favourable to the 

 detection of minute substances or actions : first, by increas- 

 ing the magnitude or intensity of the thing to be observed-; 

 and second, by the employment of more delicate tests or 

 means of observing. Thus 1. 'An intense light will 

 enable a smaller object to be seen. 2. A white picture 

 can be seen smaller than a blue. 3. A line can be seen 

 better than a point of the same diameter. The smallest 

 angle for a round body is 20"; a thread-like object is dis- 

 cernible under an angle of 3"; a glancing wire can impress 

 the eye at an angle of i".' 1 In the subject of chemistry, 

 detection of substances in very minute amounts is usually 

 facilitated by causing them to produce precipitates, or 

 coloured solutions ; and in other sciences, our powers of 

 observation are immensely extended by the aid of tele- 

 scopes, microscopes, spectroscopes, and a great variety of 

 other instruments, specially designed for the purpose, also 

 by the employment of special methods of manipulation. 

 The particular kind of test, instrument, or mode of mani- 

 pulation, is usually different with each different force, and 

 every different class of phenomena. Descriptions of these, 

 and of the various ways in which we may be deceived 



1 Bain, Senses and Intellect, 3rd edit., p. 220. 



