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JOURNAL OF THE PLYMOUTH INSTITUTION. 
affections of existence. If some minds fear the full idea of evo- 
lution, let them remember that only lately we reached the idea 
that heat, light, force, motion, &c, were but correlatable "affec- 
tions." " Nothing ever returns, nor can return, to a state of 
existence identical with a previous state." (Grove.) 
A second proposition is, that ideas are the great method of our 
knowledge. An idea is a perception of generality, a "bond of 
unity, a light which illumines the dark mass of detail." (Coleridge.) 
The ideas of form and numbers evolved early in man's history ; 
architecture, geometry, astronomy, were so far perfect sciences 
many centuries before man felt general truths in languages, in the 
affections of matter, in natural history, &c. After the ideas of 
these elementary sciences had evolved, progress came in other 
physical aspects of existence — chemistry, electricity, &c. ; their 
ideas became more easy to us in natural history (W. Smith, Hutton, 
St. Hilaire, Schwann, Goethe, Darwin) ; after this came genera- 
lization and ideas on languages (F. Von Schlegel) ; and on society 
and government (Adam Smith, Buckle). The historical order of 
the evolution has been a necessitous one. Kepler's laws came from 
his idea, that a relation of times and distance must exist ; Newton 
had the idea of the oneness of the order of all motion ; Franklin 
had the idea of the oneness of electrical phenomena ; Faraday's 
idea was that polarity must exist in every part of the circuit, and 
he rejected the two poles. Since then the idea has evolved in us 
that heat, magnetism, light, motion, are correlated "affections;" 
the emissive and undulatory theories of light have passed away, 
and the wider idea and generalization, that light is an affection of 
an existence in space, seems like an a priori truth. The science of 
crystallography is framed on a few leading ideas; botany is a 
shapeless mass, without the ideas of Schwann, Goethe, Jussieu, 
and the natural system. The great impulse which Pascal and 
Lavoisier gave to knowledge was due to their two respective ideas. 
Virchow has lately illumined much darkness by his idea, that a 
"physiological type must exist for every pathological formation." 
These instances show that great advances in knowledge are chiefly 
the result of ideas. 
The idea of the alliances and oneness of phenomena takes the 
place of the assertive period of definition and specific differences, 
e.g., heat, light, electricity, motion, &c, are correlatable ; the animal 
and vegetable kingdoms are but series of allied forms; the word 
