BIBLIOGRAPHY OF IIEUSCIIEL's WRITINGS. 591 



Herschel, W.: Synopsis of the Wi;iti\(;s of— Continued. 

 A. D. Vol. P. 



1807 U7 180 E.vijcrimni:ts for itn-caiiijaliiid the Caiiftc of the coloured concentric Rings, 

 discovered hij Sir Isaac Newton, between two Object-glasses laid upon 

 one another. By William Herschel, LL U., F. R. S. Read Feb- 

 ruary 5, 1807. 

 180-181 Introduction. 



182-185 I. Of different mctliods to make one mi of concentric rings visible. 

 185-186 II. Of seeing Rings hij Transmission. 



187-188 III. Of Shadoivs. When two or more sets of rings are to bo ex- 

 amined they may be distinguished l)y casting the shadow of a potnted 

 penknife upon one set or another. 

 188-193 IV. Of two sets of Rings. 

 193-194 V. Of three sets of Rings. 



195 VI. Of four sets of Rings. 

 195-198 VII. Of the Size of the Rings. 



196 VIII. Of Contact. 



197 IX. Of Measuring Rings. 

 197-198 X. Of the Number of Rings. 



198-199 XL Of the Effect of Pressure on the Colour of the Rings. 

 199-200 XII. Of diluting and concentrating the Colours. When the rings 

 grow wider by using a lens of larger radius, they are said to be di- 

 luted. 

 201 XIII. Of the order of the Colours. 



201-202 XIV. Of the alternate Colour and Size of the Rings belonging to the 



jyrimarg and dependent Sets. Certain of the dependent sets arc rings 



by transmission as seen reflected at the back surface of the lower 



plate. 



202-203 XV. Of the sudden Change of the Size and Colour of the Rings in 



different Sets. This is brought about by lotting the shadow of 



the knife-blade fall on one or the other set. 



204-208 XVI. Of the course of the Rays by which different Sets of Rings are 



seen. 

 206-207 XVII. Why two connected Sets of Rings are of alternate Colours. 

 207-208 XVIII. Of the Cause of the sudden CJmnge of the Colours. 

 208-209 XIX. Of the Place lohere the different Sets of Rings are to he seen. 

 209-210 XX. Of the Connection between different Sets of Rings. 

 211-212 XXI. To account for the Appearance of several Sets of Rings with the 



same coloured Centers. 

 212-213 XXII. Of the reflecting Surfaces. 

 213-214 XXIII. Of the transmitting Surfaces. 

 214-218 XXIV. Of the Action of the first Surface. 

 218-221 XXV. Of the Action of the second Surface. 

 221-222 XXVI. Of the Action of the third Surface. 



222 XXVII. The Colour of the reflecting and transmitting Surfaces is of 

 no consequence. 

 222-225 XXVIII. Of the Action of the fourth Surface. 



225 XXIX. Considerations that relate to the Cause of the formation of con- 



centric Rings. 



226 XXX. Concentric Rings cannot be formed by an alternate Reflection 

 and Transmission of the Rays of Light. 



"One of the most simple methods of obtaining a set of concentric 

 ring's is to lay a convex lens on a plain metalline mirror; but in this 

 case we can have no transmission of rays, and therefore we cannot 



