34? DISCOURSE ON THE STUDY 



there ought to be no darkness, in fact, no shadow 

 at that place ; but, on the contrary, a degree of illu- 

 mination precisely as bright as if the metal plate 

 were away. Strange and even impossible as this 

 conclusion may seem, it has been put to the trial, 

 and found perfectly correct. * 



(25.) We shall now proceed to consider more 

 particularly, and in detail, 



I. The nature and objects immediate and colla- 



teral of physical science, as regarded in 

 itself, and in its application to the practical 

 purposes of life, and its influence on the 

 well-being and progress of society. 



II. The principles on which it relies for its suc- 



cessful prosecution, and the rules by which 

 a systematic examination of nature should 

 be conducted, with examples illustrative of 

 their influence. 



III. The subdivision of physical science into distinct 

 branches, and their mutual relations. 



* We must caution our readers who would assure themselves 

 of it by trial, that it is an experiment of some delicacy, and not 

 to be made without several precautions to ensure success. For 

 these we must refer to our original authority (Fresnel. Me'moire 

 sur la Diffraction de la Lumiere, p. 124.) ; and the principles 

 on which they depend will of course be detailed in that 

 volume of the Cabinet Cyclopaedia which is devoted to the 

 subject of LIGHT. 



