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THE POPULAR SCIENCE MONTHLY 



black color. In parchment this color is 

 permanent, but in paper it is only tempo- 

 rary. Old paichment chronicles in the 

 Nuremberg Museum which have been treat- 

 ed in this way are now as legible as when 

 first they were written, though before the 

 application of the process all color had 

 faded out of the ink. The rationale of the 

 process is, that by the action of the ammo* 

 nia sulpho-hydrate, the iron of the ink is 

 changed into a black sulphuret. 



An Optical lUnsion. St. Simon, in his 

 famous " Memoires," describing the person- 

 al appearance of the twelfth Duke of Albu- 

 querque, characterizes his hair as " coarse 

 and greeny The question here arises, Was 

 the duke's hair really of this color, or was 

 St. Simon the victim of an optical illusion ? 

 That the latter was in all probability the 

 fact, is shown in a communication made to 

 the Paris Academy of Sciences by the ven- 

 erable M. Chevreul, " the oldest student in 

 France." On the day when the Duke de St. 

 Simon saw Albuquerque, the latter wore a 

 bullock' s-blood coat of coarse cloth, with but- 

 tons of the same, and his hair hung down 

 on his shoulders. " Now," says Chevreul, " if 

 we take hairs of a certain color, and arrange 

 them on a red ground in parallel lines, mak- 

 ing a small ribbon of them, and place beside 

 them exactly similar hairs on a white ground, 

 the former relatively to the latter will appear 

 green. If for white we substitute orange, 

 the hairs on the red ground will assume a 

 bluish tint ; if violet, a yellow tint ; if 

 green, a ruddy tint ; if blue, an orange tint ; 

 if violet, a greenish yellow ; and, finally, if 

 we substitute black for the white ground, 

 the hairs on the red ground will become 

 whitened. In short, if we look at a broad 

 surface of one simple color, we see it and 

 appreciate it absolutely. If we see it in 

 Juxtaposition with another color, or, still 

 better, at the centre of a broad surface of 

 another color, we see it relatively, and the 

 sensation produced by it will be quite 

 different." 



A Rat in the Telegfaph Service. A tele- 

 graph-inspector in England recently pressed 

 into his service a rat under the following pe- 

 culiar circumstances: It was necessary to 

 overhaul a cable of wires inclosed in iron 



tubes. A certain length of the cable had 

 to be taken out of the tube, and the men 

 commenced hauling at one end without 

 having taken the precaution to attach to 

 the other a wire by which it might be 

 drawn back into the tube after inspection 

 and repairs. The question arose, how the 

 cable was to be restored to its proper place ; 

 and here the ingenuity of the inspector was 

 manifested. He invoked the aid of a rat- 

 catcher, and, provided with a large rat, a 

 ferret, and a ball of string wound on a 

 Morse paper drum, he repaired to the open- 

 ing in the tube. The " flush-boxes " were 

 opened, and the rat, with one end of the 

 string attached to his body, was put into 

 the pipe. He scampered away at a racing 

 pace, dragging the twine with him until he 

 reached the middle of the length of pipe, 

 and there stopped. The ferret was then 

 put in, and off went the rat again until he 

 sprang clear out of the next flush-box. One 

 length of the cable was thus safe, and the 

 same operation was commenced with the 

 other ; but the rat stopped short a few 

 yards in the pipe and boldly awaited the 

 approach of the ferret. A sharp combat 

 here commenced, and it was feared that one 

 or both of the animals would die in the 

 pipe. But, after sundry violent jerks had 

 been given to the string, the combatants 

 separated ; the ferret returned to his mas- 

 ter, and the rat, making for the other ex- 

 tremity of the pipe, carried the string right 

 through, and so relieved the inspector from 

 his anxiety. 



Behavior of Metals with Hydrogen. 



From researches carried on conjointly by 

 Messrs. Troost and Hautefeuille, and re- 

 ported to the French Academy of Sciences, 

 it appears that potassium, sodium, and pal- 

 ladium, combine with hydrogen, while a 

 considerable number of other metals merely 

 dissolve this gas. Iron, nickel, and manga- 

 nese, oifer striking analogies in their be- 

 havior with hydrogen at different tempera- 

 tures. The facility with which they absorb 

 or give olF hydrogen gas depends greatly 

 on their physical condition. An ingot of 

 pure nickel gave out in a vacuum, at a red 

 heat, one-sixth of its volume of hydrogen. 

 Pulverulent nickel gave out 100 times its 

 volume, and remahied pyrophoric after the 



