Immersion Lenses and New Befradometers. 65 



Y-On the History, Befradions, Definition, and Powers of 

 ' Immersion Lenses and New Bef Tactometers. By Eoyston- 

 PiGOTT M.A, M.D. Cantab., M.K.C.P., FeUow of the Cam- 

 bridge 'philosopliical and tbeEoyal Astronomical and Micro- 

 scopical Societies of London, formerly Fellow of St. Peters 



College, Cambridge. 



{Part 1.) 



T —History has handed down to us the labours of Claudius 

 Ptolemy, the Father of Optics. His celebrated experiment oi ren- 

 deiing a coin yisible placed in an empty vessel by hlhng it with 



NOTICE TO BINDER. 



In consequence of an error in page 66, 

 Number XXVI., a corrected leaf is now 

 sent for insertion. 



Refraction from Air into Water. 

 Bent Oar in Water. 



His very ingenious mode of setthng these points, as it i-eaUy 

 invok s thi im^portant princirje of the mob^n ^^^-^^ ^^^^l 

 may not be uninterestmg to those unacquamted with the expen- 

 ments Observing the c?ooked image of an oar m water and the 

 Sirbus apparent rising of the money as the water is poured mto the 

 vrerheTad a semi-?yhnder of " p^re glass " constmcted, to which 

 he adjusted a graduated circle, so that the diameter of the cyhnder 

 coincted precisely with the chameter of the .-"^^^^^^ f ^^ 

 inpntioned and also with the surface of the water. A smau 

 Tw body was placed at the centre of the circle ; a second 

 sSrly fitted to one of the quadrants out of the water ; a third 

 sMed on the lower part of the graduated circle nnmersed m the 

 tter. Observations'were then made upon the angles of mc^^^! 

 and refraction of such a degree of accuracy as to e^/^^^e om^^^^ 

 tion after a lapse of nearly two thousand years. TJie ^^at^on 

 of the conditions of refraction through a water lens was thus 

 anciently effected sufficiently exact for all the practical purposes of 

 modern theory. * 



