58 Sir J, F. W. Herschel on the Action of Light in detejviinivg 



The prism fig. I. was cracked in the commencement of the 

 experiments, by being placed too near the flame of the lamp ; 

 but fortunately the light in this prism being incident at 4'5'^ 

 on the second surface, it was allowable to use another part of 

 the glass beyond the extent of the crack. 

 The rectangular piece 

 averaged from rays incident. raj-s transmitted. 



3 measurements . 100 78'o6 



4- .100 78-36 



5 .100 77-95 



The prism fig. 1, where the light was incident on the second 

 surface at an angle of 45°, 



averaged from rays incident, rays reflected and transmitted. 



8 measurements .100 76-97 



6 .100 75-23 



The prism fig. 2, where the light was incident on the second 

 surface at an anjvle of 60°, 



averaged from rays incident, rays reflected and transmitted. 



6 measurements .100 74-97 



6 .100 78-46 



The prism fig. 3, in which the light was incident on the se- 

 cond surface at an angle of 75°, 



averaged from rays incident, rays reflected and transmitted. 



6 measurements . 100 77*04 



5 .100 76-90 



Another set of measurements for the second prism gave 72'92 ; 

 and thinking that there arose rather more of extraneous light 

 in using the rectangular piece than in using the prisms, I made 

 another set of measurements with it, taking additional precau- 

 tions, and obtained 74 "02 ; but it is probable that in these two 

 last-mentioned cases some unnoticed cause of error had arisen, 

 making the results come out too small. 



Fig. 1. Fig. 2. Fig. 3. Fig. 4. 



"^--h-^f 



XVI. On the Action of Light in determini^ig the Precipitation 

 of Muriate of Platinum hy Lime-taater s being an Extract 

 from a Letter of Sir JoHs F. W. Herschel, KAL. F.R.S. 

 6;c. to Dr. Daubeny*. 



l^^HEN a solution of platinum in nitro-muriatic acid, in 

 ** which the excess of acid has been neutralized by the 



• Read before the British Association at Oxford, June 22, 1832 j and 

 communicated by request of the Author. 



