132 



PHYSICAL OPTICS, 



Comparlfon of we may aflign, by calculating the difference of the tw^o paths, 

 mea urcj. ^^^ interval for the firft difappearance of the brightefl hght, as 



it is exprelTed in the fourth line. The fecond Table contains the 

 refults of a (imilar calculation, from Newton's obfervations on 

 the (hadow of a hair ; and the third, from forae experiments 

 of my own, of the fame nature : the fecond bright line being 

 fuppofed to correfpond to a double interval, the fecond dark 

 line to a triple interval, and the fucceeding lines to depend on 

 a continuation of the progreffion; The unit of all the Tables 

 is an inch. 



Table I. Obf, 9. 



DItlance of the knives from the aperture 

 Diftances of the pa- 



N. 



per from the knives 



Diftances between 

 the edges of the 

 knives, oppofite 

 to the point of 

 concourfe 



li 



.012, ,020, 



8f 



.034, 



32, 



96, 



101. 

 131. 



.057, .081, 087. 



Interval of difappearance .ooooiaz, .0000155, .coooiSa, .0000167, .0000166, .0000166. 



Table II. Obf, 3. N. 

 Breadth of the hair ... 



Diftance of fhe hair from the aperture 

 Diflances of the fcale from the aperture - 

 (Breadths of the (hadow . - - 



Breadth between the fecond pair of bright lines 



Interval of difappearance, or half the difference 

 of the paths . - - - 



Breadth between the third pair of bright lines 



Interval of difappearance, | of the difference 



Table III. Exper. 3. 



Breadth of the objed 



Diftance of the object from the aperture 



Diftance of the wall from the aperture 



Diflance of the fecond pair of dark lines from each other 



Interval of difappearance, \ of the difference 



Exper, 



