386 ACTUAL WORKING IN ORIGINAL RESEARCH. 



important principle in science. He, however, by these 

 experiments laid the fomndation of blowpipe analysis ; he 

 also discovered in the year 1740 that oxide of manganese 

 was a substance different from oxide of iron, and in 1746 

 showed that silica was distinct from other earths. 



When once a phenomenon has been divested of all 

 sources of interference, and obtained in its purest and 

 simplest form, a large number of experiments is of great 

 importance, because if we repeat an experiment with 

 every possible variety of substance, we are sure to include 

 the most feeble and the most conspicuous instances of the 

 phenomenon, and also the exceptional and contradictory 

 cases, if there are any. The discovery of extreme and 

 exceptional instances is often of great value, because it 

 enables us to draw important conclusions, and by the 

 further investigation of such instances we sometimes 

 detect an entirely new class of phenomena which an ordi- 

 nary instance would not enable us to suggest. But until 

 the particular phenomenon has been obtained in its purest 

 and simplest form, a multiplicity of experiments yield 

 such a mass of complicated and conflicting results that 

 even the clearest and most discerning intellect is utterly 

 unable to disentangle and explain them. The pheno- 

 mena of an experiment, even in its simplest condition, are 

 usually related to or inseparable from so many other 

 phenomena, 1 especially in the biological sciences, that it 

 is extremely difficult to classify and harmonise all the 

 results, some usually remaining unexplained even in a 

 finished investigation. These circumstances indicate the 

 comparatively small value of conclusions derived from the 

 results of crude experiments. 



1 See pp. 32, 33. 



