Curiosities of Science. 29 



stopped : it may be tuned in unison with the loaded tuning- 

 fork by means of the movable stopper or card, or the fork may 

 be loaded till the unison is perfect. Then set the fork in vi- 

 bration by a blow on the unloaded branch, and hold the card 

 closely over the mouth of the pipe, as in the engraving, when 

 a note, of surprising clearness and strength will be heard. In- 

 deed a flute may be made to " speak" perfectly well, by holding 

 close to the opening a vibrating tuning-fork, while the fingering 

 proper to the note of the fork is at the same time performed. 



THEORY OF THE JEW^S HARP. 



If you cause the tongue of this little instrument to vibrate, 

 it will produce a very low sound ; but if you place it before a 

 cavity (as the mouth) containing a column of air, which vi- 

 brates much faster, but in the proportion of any simple mul- 

 tiple, it will then produce other higher sounds, dependent upon 

 the reciprocation of that portion of the air. Now the bulk of 

 air in the mouth can be altered in its form, size, and other cir- 

 cumstances, so as to produce by reciprocation many different 

 sounds ; and these are the sounds belonging to the Jew's Harp. 



A proof of this fact has been given by Mr. Eulen stein, who 

 fitted into a long metallic tube a piston, which being moved, 

 could be made to lengthen or shorten the efficient column of 

 air within at pleasure. A Jew's Harp was then so fixed that 

 it could be made to vibrate before the mouth of the tube, and 

 it was found that the column of air produced a series of sounds, 

 according as it was lengthened or shortened ; a sound being 

 produced whenever the length of the column was such that its 

 vibrations were a multiple of those of the Jew's Harp. 



SOLAR AND ARTIFICIAL LIGHT COMPARED. 



The most intensely ignited solid (produced by the flame of 

 Lieutenant Drummond's oxy-hydrogen lamp directed against a 

 surface of chalk) appears only as black spots on the disc of the 

 sun, when held between it and the eye ; or in other words, 

 Drummond's light is to the light of the sun's disc as 1 to 146. 

 Hence we are doubly struck by the felicity with which Galileo, 

 as early as 1612, by a series of conclusions on the smallness of 

 the distance from the sun at which the disc of Venus was no 

 longer visible to the naked eye, arrived at the result that the 

 blackest nucleus of the sun's spots was more luminous than 

 the brightest portions of the full moon. (See " The Sun's 

 Light compared with Terrestrial Lights," in Things not generally 

 Known, pp. 4, 5.) 



SOURCE OF LIGHT. 



Mr. Robert Hunt, in a lecture delivered by him at the 

 Russell Institution, " On the Physics of a Sunbeam," mentions 



