Lesson DC. 



OPTIC8L 



149 



104. I*. What do you mean by the in- 



i of the net tile? 



/' Its deviation from the horizontal 

 position ; thus one point of the needle 

 appro iches the earth, or what is tech- 

 nically called dips, and this we find 

 increases or decreases according to our 

 position near or from the equator and the 

 poles. 



!IAL QCKSTIONS OX LESSON* VIII. 

 1. Is the magnetic influence uniform in 

 a magnetic 



hat is the difference between tbe 

 ends and the centre of a magnet ? 



hat are the ends of a magnet 

 called? 



4. 1- tin-re anything peculiar about the 

 attractive force of magnet-? 



5. Is the magnetic force increased by 

 usiner two magnets instead of one? 



6. Explain the meaning of the terms 

 direction, declination, and inclination of 

 a magnetic needle. 



[GRANDFATRKH "\VHITI:HRAI> refrains 

 from entering into the discussion of animal 

 electricity, because the subject is too 

 abstruse for the greater part of his pupil?, 

 and not so practically useful as the sub- 

 jects already considered]. 



OPTICS. 



INTRODUCTION. The science of Optics reveals to us the intimate nature and 

 affections of light ; and as we judge of the various objects around us, chiefly by our 

 sense of sight or vision, the science of optics becomes interesting to us all, and enables 

 ijTprehend many of the highly interesting, curious, and important phenomena 

 connected with vision; and hence its name, which is derived from the Greek word 

 optomai (OTTO/UK), to see; therefore the science of optics signifies the theory of light 



sion. 



In investigating this science, we have to consider the following points. I. The 

 general properties of light, and its effect on the organ of vision. 2. The reflection of 

 light from the surfaces of bodies. 3. The refraction of light, or the change it under- 

 goes in passing through transparent bodies. \;\ of colour^ 

 Modifications of reflected and refracted light 



1 IX. 



SOME bodies a< 1 passage of light, and of other bodies being seen through 



them ; they are therefore called transparent.* Some are exactly tl.< : thi, 



and are called opaque; others only admit of bodies being imperfectly s. . 

 them, nd are called setni-transparrn;. or h ;. If. transparent ; others ar. 



-ht, and are called luminoou; and some can only be seen by means 

 obtained from the luminous bodies. 



iv v now to treat of the theory of direct light, 



The word lra*,parmt U derived from l.r - Iran,, through or beyond, and parnu 



apparent. TbU word U frequently u-w in lead of d*pt>o*o*,, which ilfnines the Mftir, .- 

 from the Orrek word dlnr > f through. 



