NATURAL PHILOSOPHY. 153 



the eye sees through the openings a most beautiful play of colors. They 

 dance and waver in the outline of the perforated black card in a manner 

 that appears magical. These effects are due to the fact that the eye retains 

 for a certain period the impressions of color which it receives, and one im- 

 pression has not time to be effaced before another succeeds it. The inventor 

 is J. Gorham, \vlio has thus succeeded in making a toy exhibit all the effects 

 of the well-known prismatic wheel. 



OCCASIONAL LUMINOUSNESS OF THE ATMOSPHERE AT NIGHT, AS 



OBSERVED ON THE ANDES. 



In a communication on the above subject, presented to the American 

 Association for the Promotion of Science, 18-39, by the Rev. George Jones, 

 U. S. N., the author first referred to the case mentioned by Humboldt, in his 

 Cosmos, which occurred in Germany about the year 1833, when the atmos- 

 phere was so luminous that people could see to read fine print. While at 

 Quito, in 18-30-7, he (Mr. Jones) noticed a singular luminousness, not con- 

 stant, but occasional, and made records of the phenomenon. About that 

 time, and before he had spoken to any one about it, an Irish gentleman, Col. 

 Lanegan, who had taken part in the revolutionary struggle in Ecuador, men- 

 tioned a similar case which he had observed at Macheche, about three days' 

 journey from Quito, when the night was so bright that his servant called 

 him up, and they started on a journey, supposing it to be day, but after a 

 while it became so dark that they could not see at all. Col. Lanegan attrib- 

 uted it to the zodiacal light, but he was wrong as to the cause. 



The Colonel's statement led Mr. Jones to make some inquiries on the sub- 

 ject, of Col. Stacy, at Quito, who told him that, in his night-marches on the 

 mountains, the air was often so bright that they could see everything dis- 

 tinctly, and again it was so dark that they went stumbling over every stone 

 that came in their way. 



Mr. Jones said his own observations were made on cloudy nights, when 

 he could get no light from the stars, and the luminousness of the atmos- 

 phere was such, at times, that he could read the headings of newspapers, 

 the New York Herald, and New York Journal of Commerce, for instance. 

 The next night would perhaps be so dark that he could not see his hand 

 twelve inches from his face. He could not account for this phenomenon, 

 unless on the supposition that all space was filled with luminous matter, 

 that vibratory matter is self-luminous, and that it is sometimes swept by us 

 in dense waves. This explanation, he admitted, was far-fetched, but he 

 could think of no other. 



MOTHER-OF-PEARL. 



A peculiar phenomenon is noticed when wax, stearine, or similar sub- 

 stances, especially if colored black by lampblack or graphite, has been 

 poured on a sheet of mother-of-pearl. It is that the inner surface of the 

 congealed substance, in a certain position to the eye, appears with the same 

 bright iridescence as the plate itself. This goes to prove that those colors 

 are not owing to a particularity of the substance of mother-of-pearl, but 

 solely to the condition of its surface, which consists of fine striae that bend 

 the rays of reflected light, and resolve them into the various colors. Its 

 being reflected light, is proved by the complete disappearance of the varie- 

 gated colors when the surface is exposed to homogeneous light, such as that 



