28 Mr. Charles L. Barnes on 



(b) The necessity of mathematics in divine 



things. These are enumerated as geography, 

 chronology, cycles, and natural phenomena, 

 arithmetic, and music. 



(c) The usefulness of mathematics in ecclesi- 



astical things, e.g., the certification of faith, 

 and the correction of the calendar. 



(d) The usefulness of mathematics in the State, 



for the sciences of hydrography, geography, 

 and astrology. 

 V. On perspective (i.e., optics), treated under four 

 heads: The organs of vision, the propagation of 

 light in straight lines, reflection and refraction, 

 and the propagation of the impressions of light. 

 VI. Of experimental science. 

 Whewell says of this work that its plan was " to urge 

 the necessity of a reform in the mode of philosophising ; 

 to set forth the reasons why knowledge had not made a 

 greater progress ; to bring back attention to sources of 

 knowledge which had been unwisely neglected ; to discover 

 other sources which were yet wholly unknown ; and to 

 animate men to the undertaking by a prospect of the vast 

 advantages which it offered." The work is thus a method, 

 rather than a treatise on science ; but Part V., on 

 perspective, describes the anatomy of the eye, and is his 

 own work ; he also discourses on vision, the laws of 

 reflection and refraction, and the construction of mirrors 

 and lenses. Part VI. is again devoted rather to the 

 philosophy of the subject than a description of experi- 

 ments ; but it includes an investigation into the nature 

 and causes of the rainbow. 



The Opus Minus is a summary of the Majus ; Tertium, 

 a preamble and supplement to the other two. Bacon's 

 fiery energy appears in the fact that all three must have 

 been written within eighteen months, though no trace of 



