1 



POPULAE SCIENCE NEWS. 



[December, 1889. 



naphtha is entirely iVee from that element. 

 The important fact thus seems to be settled 

 that silver chloride is not changed to an oxy- 

 salt by the action of light. 



In a paper recently read by Dr. D. G. 

 Brinton, upon the origin of the ancient 

 Etruscan race of Italy, he takes the ground 

 that they were related to, or descended from, 

 the Libyan family, the modern descendants 

 of which aie the Kabyles of Algeria. Dr. 

 Brinton points out the numerous points of 

 resemblance between the two peoples, and 

 clearly shows that linguistic science, concurs 

 with tradition, archeology, sociologic traits, 

 and anthropologic evidence, in assigning a 

 genetic relationship of the Etruscans to the 



ancient Libyans. 



-t^^ — 



An interesting and novel mineralogical 

 specimen in the shape of a pseudomorph of 

 native copper after azurite, is described by 

 Mr. W. S. Yeates. The reduction was 

 probably accomplished by heated volcanic 

 gases thrown up from below. 



1604, when it was noticed that Bolognese 

 phosphorus, (sulphide of barium) after be- 

 ing exposed to sunlight, and removed to a 

 dark room remained luminous for a consider- 

 able time. The sulphides of strontium and 

 calcium also possess the property in the 

 highest degree, the latter substance being the 

 base of the well known luminous paint, 

 which has come into quite extensive use. 

 The color of the phosphorescent light is very 

 variable, and even with the same body, it 

 changes with the manner in which it is pre- 

 pared. In strontium compounds, green and 

 blue tints predominate ; and with the sul- 

 phides of baruim, orange, yellow, and green, 

 are more often observed. 



The duration of phosphorescence also 

 varies greatly. With the sulphides of calcium 

 anj strontium it may last as long as thirty 

 hours, while with most other substances it 



PHOSPHORESCENCE. 



Phosphorescence is the property which 

 a large number of substances possess of 

 emitting light when placed under certain 

 conditions. 



The element phosphorus, from which the 

 term is derived, when exposed to the air in 

 the dark, gives oft" a dim light, as can easily 

 be obseived by rubbing a match over a rough 

 surface, taking care not to use force enough 

 to cause it to ignite. This is, however, due 

 to a slow oxidation, or combustion, and is 

 not, strictly speaking, a true phosphoi'escence, 

 which is not accompanied by chemical 

 change. 



Certain insects, such as fire-flies, and many- 

 marine animals, as well as decaying organic 

 matter, give oft' a more or less brilliant light, 

 and even some plants have been observed to 

 emit flashes of light on warm summer even- 

 ings. We once observed a piece of fish 

 placed in an ice-chest to shine with a very 

 brilliant light. In this instance no decay had 

 taken place, as the fish was perfectly fresh 

 and sweet, and was eaten the next day. 



In the above cases there is undoubtedly 

 more or less chemical change or oxidation, 

 but there are numerous substances which 

 give off light without any alteration in their 

 composition. Fluor-spar, and certain varie- 

 ties of diamonds, for instance, when heated 

 to 600° or 700° F., emit a bluish light, and 

 when a lump of sugar is crushed, or two 

 quartz crystals rubbed together in the dark, 

 quite a brilliant phosphorescence may be 

 observed. The largest size lozenges when 

 broken apart show the phenomena very well. 



The most interesting variety of phosphores- 

 cence is that caused by insolation or exposure 

 to the sun's rays. This was first observed in 



air) metals, and liquids, do not phosphoresce 

 at all. 



The cause of phosphorescence by insola- 

 tion cannot be definitely explained, but, if we 

 accept the undulatory theory of light, we 

 may suppose, that, the light waves striking 

 against certain bodies, have the power to in- 

 duce similar vibrations in their substance, 

 just as in the case of sound, a musical note 

 may cause a string tuned to the same note to 

 vibrate in unison with it, or, as a current of 

 electricity passing through a coil of wire may 

 induce another current in a neighboring coil. 

 We may suppose that the molecules of phos- 

 phorescent substances are adjusted, or tuned 

 as it were, to the vibratory periods of certain 

 light waves, so that when they fall upon 

 them, a similar vibration is induced in their 

 substance, which continues for a longer or 

 shorter time after the original light is with- 



A'Viis^Nr, 



only lasts for a few seconds, or even fractions 

 of a second. To study this latter class of 

 substances, an ingenious machine was de- 

 vised by M. Becquerel, by which a body may 

 be exposed to light and immediately viewed 

 in darkness for a definite length of time. It 

 consists substantiallv of a wheel revolving at 

 a known rate of speed to which the substance 

 under observation is attached. As it re- 

 volves, it passes alternately from light to 

 darkness, and as the speed of the wheel is 

 known, the time of the exposure, and the 

 duration of the phosphorescence can be 

 readily calculated. With this instrument, it 

 is found, that, a large number of substances 

 become phosphorescent by insolation, includ- 

 ing many minerals, silk, amber, dry paper, 

 and even the teeth. Uranium compounds 

 emit a brilliant light, which, however, only 

 continues from three to four thousandths of a 

 second. On the other hand, quartz, sulphur, 

 phosphorus, (when out of contact of the 



drawn. Currents of electricity under certain 

 conditions, are also very eftective in inducing 

 phosphorescence, and the light emitted by 

 various substances, when placed in highly- 

 exhausted glass tubes, through which such a 

 current is passed, is, in many cases, brilliant 

 and magnificent to the highest degree. 



INDIAN JEWELRY. 



In the United States mineralogical exhibit 

 at the Paris Exposition, are several unique 

 specimens of jewelry collected among the 

 Indians of Arizona and New Mexico. They 

 are composed principally of turquoise, a 

 phosphate of alumina colored blue by copper, 

 and are interesting as indicating that this 

 beautiful mineral was prized as a gem by the 

 aboriginal inhabitants of this country, as well 

 as by those natives of oriental lands who dis- 

 covered it independently. 



In the engraving. Fig. i represents a neck- 

 lace of perforated beads of turquoise, with a 



