AND ITS CONGENERS. 219 



which is long and flexible, is connected with a larger 

 iron bottle, containing compressed air. Hoisting the 

 small bottle to a convenient height, the tap of the 

 larger bottle is carefully opened, the air passes through 

 the flexible tube to the smaller bottle, exerts its pres- 

 sure upon the surface of the liquid therein contained, 

 drives it up the other tube, and causes it to impinge 

 with any required degree of force against the disk of 

 the spray-producer. From this it falls in a fine rain. 

 A great many liquids, including coloured ones, 1 have 

 been tested by this arrangement, and very remarkable 

 results have been obtained. I will confine myself here 

 to a reference to two liquids, which commend them- 

 selves on account of their cheapness and of the bril- 

 liancy of their effects. Spirit of turpentine, forced 

 from the iron bottle and caused to fall in a fine shower, 

 produces a circular bow of extraordinary intensity and 

 depth of colour. With paraffin oil or petroleum an 

 equally brilliant effect is obtained. 



Spectrum analysis, as generally understood, occu- 

 pies itself with atomic or molecular action, but physi- 

 cal spectrum analysis may obviously be brought to 

 bear upon our falling showers. A composite shower 

 — that is to say, one produced by the mingled spray 

 of two or more liquids — could, it seems plain, be 

 analysed and made to declare its constituents by the 

 production of the circular rainbows proper to the re- 

 spective liquids. This was found to be the case. In 

 the ordinary rainbow the narrowest colour-band is pro- 

 duced by its most refrangible light. In general terms, 

 the greater the refraction, the smaller is the bow. 

 Now, as spirit of turpentine and paraffin are both 

 more refractive than water, it might be concluded that 



1 Rose-aniline, dissolved in alcohol, produces a splendid bow 

 with specially broad supernumeraries. 

 15 



