NATUEAL PHILOSOPHY. 



tyndall's discovery. 



'• It consists," to use his own words, *' in subjectinfi^ the vapors 

 of volatile liquids to the action of concentrated sunli^^lit, or to the 

 concentrated beam of the electric light ; " and some of the results 

 which he records are of such singular, almost inconceivable, 

 beaut)% that for this reason alone, and putting aside their im- 

 portant application to many atmospheric phenomena, and proba- 

 bly to art, they have a claim to be noticed in these pages. 



He uses the experimental tube. It is connected with an air-pump 

 and with a series of tubes used for the purification of the air, and 

 at one end of the tube, which lies hoT-izontally and is closed by 

 plates of glass, is placed an electric lamp, so arranged that the 

 axis of the tube and that of the parallel beam issuing from the 

 himp are coincident. 



The substances whose vapors were passed into the tube, and 

 there exposed to strong light, are known to chemists as nitrite 

 of amyl, iodide of allyl, iodide of isopropyl, hydrobromic acid, 

 hydrochloric acid, hydriodic acid. When these vapors are ex- 

 posed to the above-described action, clouds of the most beautiful 

 appearance, and at some points vividly iridescent, show them- 

 selves in the tube. When the nitrite of amyl vapor is mixed with 

 a little air the cloud is white; but if air is freely admitted, and 

 the nitrite vapor thus attenuated, the cloud varies in color from a 

 milky-blue to a pure, deep blue. " There could scarcely," says 

 the author, "be a more impressive illustration of Newton's mode 

 of rejrarding the generation of the color of the firmament than 

 that here exhibited ; for never, even in the skies of the Alps, have 

 I seen a richer or a purer blue than that attainable by a suitable 

 disposition of the light falling upon the precipitated vapor. May 

 not the aqueous vapor of our atmosphere act in a similar man- 

 ner ? " 



The cloud yielded by iodide of allyl was extremely beautiful. 

 The whole column revolved round the axis of the decomposing 

 central beam, and was nipped so as to have an hour-glass ap- 

 pearance, while round the gobular dilatations dt'licate cloud-fila- 

 ments twisted themselves in spirals. It also folded itself into 

 convolutions resembling those of shells. When hydrogen is 

 made the vehicle of this vapor, the cloud assumes a pearly lustre, 

 such as Dr. Tyndall has often noticed in curtain conditions of the 

 atmosphere in the Alps. 



The action of light upon the vapor of iodide of isopropyl oc- 

 casions in the course of a few minutes some singularly graceful 



13C 



