230 TEAR-BOOK OF FACTS. 



series of sections which he had prepared, and by which he showed 

 that by the microscope he could at once determine what shell had 

 produced them. He also explained the rationale of the iridescence 

 of mother-of-pearl, — a discovery due to Sir David Brewster, who 

 proved that it was due to the diffraction of the rays of light caused 

 by the out-cropping edges of the laminse, and in some cases to the 

 minute plication of a single lamina. This phenomenon was also 

 shown by Barton's patent buttons, where the iridescence was pro- 

 duced by thousands of minute lines, so near each other as to require 

 a high magnifying power to resolve them. By taking an impression 

 with black wax under considerable pressure, the author succeeded in 

 obtaining the same iridescence as exhibited by the button itself. 

 This experiment Sir David Brewster had tried with success in 1815, 

 by taking an impression in wax from a mother-of-pearl button, and 

 by which he demonstrated the cause of the phenon 



The commercial value of pearls, the author stated, was still as 

 high as in the days of Cleopatra. A good Scotch pearl, with fine 

 lustre, of the size of a pea, fetches from SI. to 41, The famous 

 wager between Antony and Cleopatra gives us an insight into the 

 value of pearls. The two pearls which that luxurious Queen re- 

 solved to dissolve in vinegar, and serve up at the costly banquet, 

 were valued at ten millions of sesterces, about 76,0002. sterling. The 

 pearl in the possession of Mr. Hope, the largest of modern times, is 

 not worth a fourth of that sum. The weight of this pearl is 3oz. ; 

 it is 4A inches in circumference, and 2 inches in length. 



Notwithstanding the great value of the pearls, the shells of the 

 animals yield now a far more profitable return than the jewels. In 

 1856, the total value of the pearls imported into this country was 

 56,162Z., whereas the imports of 2102 tons of mother- of-pearl shells 

 •were valued at 76,544/. Mr. Bryson suggested that trials should be 

 made to produce artificial pearls from the Iridina, a nacreous shell, 

 haying a much higher lustre than any hitherto found. It inhabits 

 the Nile and Senegal rivers. 



NEW LEAF INSECT. 



Mr. Andrew Murray has exhibited to the Royal Physical 

 Society a beautiful photograph of the underside of a Butterfly, in 

 otiy like a dead leaf. He had received it from Dr. 

 William Traill, U.K. I.e., pr< sently stationed at Russelcondah, in 

 tin- Madras Presidency. Dr. Traill, in transmitting the photograph, 

 writes : — "1 wished to have sent you a curious insect, brought to 

 me as a Leaf Insect. In Singapore and the Straits, where a \ 

 of these singular forms are found, they are all allied to the OrtAop- 

 tera, or the ^em ra Mnvtm, Emputa, Pkatma, >Ve. I am a good deal 

 accustomed to their various forme, but on this ooc s com- 



pletely taken in, and until the animal moved, I thought it a dea 



leaf. To my surprise, I found it to ho a butterfly I W h D I 



its two anterior wingS ;\\hieh are slightly falcate at the tip) were 



pushed forward in front of i tral line on them 



ly met a similar central line on the posterior wings, so as to 



