356 



SCIENCE. 



diminish the rapidity by vibrating themselves more slowly, 

 and thus render the rays visible. Ultra violet rays could 

 consequently be transformed into violet, blue or green ; 

 blue ravs into yellow or red. What generally happens, 

 however, is that they change red rays to purely calorific 

 ones and thus make them invisible. 



We must here make several important observations. 

 First of all, violet rays do not only produce the greatest 

 fluorescence, but also the greatest phosphorescence. Red 

 rays produce neither the one nor the other. Luminous 

 or dichroic substances give a light differing from that 

 which they receive. It has been demonstrated, finally, 

 that the closest relationship exists between the two phen- 

 omena — That fluorescence can be considered as an in- 

 tense phosphorescence which can be seen in broad daylight, 

 but which dies with the light which gave it birth, while 

 phosphorescence is only a feeble but persistent fluores- 

 cence. 



" Solar phosphorus " generally reproduces luminous vi- 

 brations even when it has 'ceased to receive the latter, 

 and it can transform calorific rays into luminous ones. A 

 diamond acts in this way, also fluor-spath, and nearly all 

 artificial phosphorus. One of the last named gives forth 

 a light of various colors, if it is heated to different degrees 

 after being exposed to the light. Sulphate of strontium 

 produces a deep purple light at 20"', a violet light at 15 , 

 blue at 40 , bluish-green at 70 , greenish-yellow at ioo°, 

 and reddish-yellow at 200 , 



Moreover, phosphorescence, like fluorescence, can be 

 produced by means of an electric light rich in chemical 

 rays. If you expose to such a light a flower, a butterfly 

 or any other object covered with phosphorescent powder, 

 it will assume a magnificent appearance. The English 

 chemist, Crookes, prepared diamonds and rubies in this 

 way, by enclosing them in an air-tight glass ball placed 

 in the immediate vicinity of the negative pole, from which 

 a luminous current issued. The effect was superb, recall- 

 ing all sorts of fairy stories. Some African diamonds 

 shone with a brilliant blue light, and a large greenish one 

 produced such an intense radiance that it almost looked 

 like a lighted candle. In fact the light was quite suffi- 

 cient to read by, and the history of that famous stone in 

 the Temple of Hieropolis seemed really probable. A col- 

 lection of small diamonds from various countries, placed 

 in any receptacle that is air-tight, will produce parti-colored 

 fiery lights, blue, pink, red, orange, yellow, green and pale 

 green, all mingling together. 



In a third recipient, Crookes placed a quantity of un- 

 cut rubies, which, when the electric light fell upon them 

 shone with such a gorgeous red flame that they appear- 

 ed to be incandescent. Artificial rubies prepared by 

 Feil in Paris gave as brilliant a light as the real ones, 

 and white crystals became rose-colored or deep red. 

 Such wonderful carbuncles would have astonished even 

 the authors of the old legends. 



A curious thing occurred lately in the works of M. 

 Fleury, at Cette (Herault). The feed-water of the boiler 

 giving much incrustation, M. Fleury was advised to put 

 into the boiler some fragments of zinc as a de-incrustant, 

 and did so. In a few days, spite of oiling, the steam- 

 engine began to ivork very badly, the piston catching a great 

 deal, and it soon became necessary to stop and make exam- 

 ination. The piston was found to be covered with a thick 

 adherent layer of copper. It was put on the lathe, and at 

 certain ovalised points, the metallic layers were so thick 

 that the tool worked in copper alone. The explanation 

 given by M. Fleury is this : The boiler was connected with 

 the engine by copper pipes. Particles of zinc carried off by 

 the steam would form with the copper numberless small 

 galvanic couples ; hence the transport of copper to the 

 piston, which would principally attract them by reason of 

 its motion, and of the heating produced. It is remarked in 

 Les Mondes, that the eminently electric properties of ex- 

 panding steam may have helped in development of the 

 phenomenon. 



DRAPER'S SELF-RECORDING, MERCURIAL 

 BAROMETER. 



We are indebted to Dr. Daniel Draper for preparing an 

 abstract of his weekly Meteorological report for this 

 journal, the third of which appears this day in another 

 column. 



Dr. D. Draper is director of the Meteorological Obser- 

 vatory of the Department of Public Works, Central Park, 

 where all observations are made by self-recording instru- 

 ments, especially designed and arranged for this purpose. 



The great object Dr. Draper had in view when design- 

 ing these instruments, was to combine simplicity of 

 construction with perfect efficiency. His great success 

 is well known to all familiar with Meteorological Science, 

 and we propose in the course of a few articles to fully 

 describe these instruments, and illustrate the subject 

 with excellent wood cuts. 



We commence the series with a description of the ap- 

 paratus for recording Barometric observations. 



" I was led to construct this form of barometer from the 

 fact that with the photographic one it cannot be told 

 what the atmospheric fluctuations are until the next 

 morning, when the photographic plate is developed. 

 Even then, if there has been much variation in temper- 

 ature, it alters the sensitiveness of the collodion film, so 

 that it is very difficult to read the tracing. The con- 

 struction of the pencil instrument is as follows : 



In the pencil barometer the glass tube is 36 iuches in 

 length, the upper portion being of larger diameter than 

 the lower ; it is held firmly in a fixed position, and filled 

 in the usual manner with quicksilver; its lower or open 

 end dips into a tube or reservoir containing the same 

 metal. This reservoir is suspended on two spiral steel 

 springs, and has freedom of motion up and down. When 

 the pressure of the atmosphere diminishes, a portion of 

 the mercury flows out of the tube into the reservoir ; 

 this becoming heavier, stretches the steel springs, causing 

 the ink pencil fastened to them to maik downwards. If 

 the pressure increases the reverse movement takes place. 

 The ink pencil makes its mark on a ruled paper register, 



