LIBER TERT1US. 553 



sed in mathematicis tantum observationibus et demonstrationibus 

 insudatur. Eae autem ostendunt quomodo hsec omnia ingeniose 

 concinnari et extricari possint, non quomodo vere in natura 

 subsistere ; et motus tantum apparentes, et machinam ipsorum 

 fictitiam et ad placitum dispositam, non causas ipsas et veri- 

 tatem rerum indicant. 1 Quocirca non male Astronomia (qualis 

 nunc habetur) inter Artes Mathematicas, non sine dignitatis 

 euae dispendio, numeratur ; cum debeat potius (si proprias partes 

 tueri velit) constitui Physicae pars quasi nobilissima. Qui- 

 cunque enim Superlunarium et Sublunarium conficta divortia 

 contempserit, et Materia Appetitus et Passiones maxime Catho- 

 licas (quae in utroque globo validae sunt, et universitatem rerum 

 transverberant) bene perspexerit, is ex illis quae apud nos cer- 

 nuntur luculentam capiet de Rebus Coelestibus informationem, 

 et ab iis e contra quae in coslo fiunt haud pauca de Motibus 

 Inferioribus (qui nunc latent) perdiscet; non tantum quate- 

 nus hi ab illis regantur, sed quatenus habeant passiones com- 

 munes. 2 Quamobrem hanc partem Astronomiae, quae Physica 



1 It is difficult to know what mode of investigation Bacon here intends to recom- 

 mend. The problem of astronomy necessarily is, before any investigation as to the 

 causes of the motions of the heavenly bodies can be undertaken, to determine what 

 those motions really are. The distinction between real motions and apparent motions 

 must be recognised before any progress can be made. And this distinction is not 

 between a fact and a theory in the common acceptation of the words, but between a 

 right theory and a wrong one. Bacon complains that the physical causes of the 

 occasional immobility and regression of the planets have not been inquired into : but 

 in this complaint is involved the theoretic assumption that the planets really are 

 stationary and really do regress. This assumption is made in order to account for 

 their appearing to us to change the direction of their motion. It is the obvious 

 explanation, but nevertheless a wrong one ; and if the phenomena in question are not 

 physical phenomena but optical, to what purpose is it to attempt to assign physical 

 causes for them ? And so in the other cases which he mentions. The value of any 

 hypothesis for the explanation of the phenomena of course depends on its simplicity 

 and its completeness, and the attempt to reduce all the celestial motions to perfect 

 circles was at the time at which it was made a great step in advance ; though the idea of 

 circular motion was unduly retained when it was found to be producing not simplicity 

 but complication. But consciously or unconsciously the mind is always introducing 

 principles of arrangement (ideas or hypotheses) among the objects of its attention, and 

 the error of the passage in the text is in effect the common one of assuming that the 

 form of hypothesis with which the mind happens to be familiar is on that account an 

 absolute fact. It is well to remark, as the Newtonian philosophy is often spoken of 

 as the great result of Bacon's methods, that none of Newton's astronomical discoveries 

 could have been made, if astronomers had not continued to render themselves liable 

 to Bacon's censure. 



2 This prediction has been fulfilled by the history of physical astronomy, and the 

 information gained respecting the "motus inferiores" may be divided into two parts, 

 " quatenus hi ab illis regantur" and " quatenus habeant passiones communes." To 

 the first belong the theory of the tides and those of precession and nutation, to the 

 second that of the earth's figure, which depends on the law of universal gravitation, 

 and which therefore may be said to be a result of our knowledge of celestial phe- 

 nomena. The way in which what takes place in one part of the solar system is, 

 so to speak, reflected in others, is one of the most interesting subjects in physical 

 astronomy. 



