222 FACTS AND THEOKIES. 



and to other facts, "re mains unaffected. As when one 

 passes through a mountainous region, he sees new peaks 

 and crests, and every thing seems to change as he ad- 

 vances, yet every peak and crest was just as high, as 

 steep, as long and as broad, before he came. Whichever 

 theory as to the formation of the solar system prevails, 

 or if hereafter a better one shall be devised, every fact 

 now known as to the position of the orbits, and the 

 direction of the rotation of the planets, or as to fluid 

 bodies becoming spheroidal, or as to the internal heat of 

 the earth, or the condition of the planets and the sun, 

 or as to the spectroscopic lines in certain nebulae, will be 

 unaffected, and must have due consideration in every 

 future theory. 



So, too, in regard to light. The corpuscular theory has 

 come and gone; the undulatory bids fair to follow it; 

 but if it does, not one particle of knowledge will be lost. 

 The laws of optics now known will not be affected. The 

 angle of incidence will still be equal to the angle of re- 

 flection. The index of refraction for all known bodies 

 will still be found by dividing the sine of the angle of 

 incidence by that of refraction. Convex lenses and con- 

 cave mirrors will continue to magnify. The prism will 

 continue to give the bright* colors, and the spectroscope 

 to give the black lines in the solar spectrum with entire 

 indifference to Newton's corpuscules or Huyghen's 

 undulations. 



Every fact now known in regard to electricity will be 

 unaffected, though all present theories should be sup- 

 planted by one not yet thought of. Everything true 

 now will be true then, and must find its place and 

 weight in any satisfactory theory. 



The point I wish to emphasize is this : The destruc- 

 tion of a theory is never a loss to science. On the con- 

 trary, it is a gain. If to-day an angel should come to 

 our planet, and calling together the students of science 



178 



