SCIENCE. 



, kind, and of dimensions suited to the musical scale 

 rurioitict which he wishes to embrace, he perforates them all at 

 their summit or bottom, at the place where they are 

 (in ii6'~ * ^ e ^ xt 'J on 'he cylinder. He then takes spherical 

 Harmonica, moulds, and grinds down the glasses upon a turning 

 lathe both on the inside and on the outside, till they 

 are exactly of the same thickness. He next grinds 

 them gradually down on their rim perpendicular to 

 their axis, until when placed on the cylinder they give 

 out the exact sound which is wanted, which is done 

 by comparing the sounds with those of a well-tuned 

 organ. The same process is applied to every one of 

 the glasses ; so that an instrument fitted up in this way 

 is in every respect preferable to those made in the ordi- 

 nary manner. 



M. Biot, from whom we have taken the preceding 

 description of the harmonicon, remarks that persons of 

 a nervous temperament are deeply affected with the 

 tones of this instrument. 



10. Description of the Melodion. 



Description Thug musical instrument was invented about twelve 

 ot the me- y ears a g O by \j. Dietz, a German, and he has given 

 it the name of melodion from the sweetness and har- 

 mony by which it is characterized. We had the good 

 fortune to hear the instrument in actual use at Geneva 

 in 1814, a short time after its invention, and we are 

 surprised that it has not come into more general use. 

 This instrument was so complete that it imitated a 

 whole band of music, and its tone had a sweetness and 

 a force which we have never heard equalled. The 

 only printed notice that we have seen of it is that given 

 by Biot, which we shall follow. The melodion em- 

 braces five octaves, the different notes of which are 

 produced by the vibrations of metallic rods* of the 

 same material, but of unequal lengths, fixed at one end 

 and free at the other. The vibratoiy motion was com- 

 municated to them by a metallic cylinder or wheel, 

 which the performer turned by means of a pedal. The 

 surface of the cylinder, however, is not applied direct- 

 ly against the rods. Each of the rods carries at its 

 free extremity and at right angles to its direction, a 

 narrow and thin plate of copper screwed to it, and 

 having its surface covered with a small piece of felt 

 impregnated with colophane. This small band being 

 placed near the circumference of the revolving cylin- 

 der is made to descend by touching the key which 

 belongs to it till it comes into contact with the revolv- 

 ing cylinder and gives out its sound. The sound con- 

 tinues as long as the plate of copper is pressed against 

 the cylinder, and it may be increased or softened by 

 increasing or diminishing the motion of rotation of the 

 cylinder. The moment the finger is taken from the 

 key the plate of copper quits the cylinder and rests upon 

 a soft body which instantly makes its vibrations cease. 

 As the sounds of metallic rods are directly propor- 

 tional to their thicknesses and reciprocally to the : r 

 lengths, the rods must be lengthened and diminished 

 in, diameter in order to produce grave sounds. In this 

 case it is difficult to elicit their fundamental sound, 

 and when the flexibility of the rods is great the vi- 

 brations are uncertain. M. Ditty, has in a very in- 

 genious manner remedied these disadvantages. He 

 loads the metallic rods with email metallic discs per. 

 tbrated in the direction of their diameter, so that they 

 can be kept by friction on any part of the rod. By 



sliding these discs along the rod, the intonation of 

 the rod varies with the position, and the sound be- 

 comes more grave in proportion as these disct increase ^_ r i *' _^ 

 in magnitude. This double effect enabled him to ob- 

 tain very grave sounds with very stiff rods, and to 

 regulate the tuning of the instrument with the greater 

 facility. 



AEROSTATION. 



In our article on AERONAUTICS Vol. I. we have Aerostatic* 

 given a very full account of the history of aerial navi- 

 gation, and of the method of constructing, filling, and 

 using balloons, as well as the different pieces of appa- 

 ratus connected with them. Since that article was 

 printed, no essential improvements have been made 

 upon balloons, although numerous aerial voyages have 

 been performed in this country by the two Mr. Sad- 

 dlers, Mr. Graham, and Mr. Green; of whom Mr. Sad- 

 dler, jun. and Mr. Graham have fallen victims to their 

 intrepidity. 



Before the general introduction of gas illumination, 

 it was both an expensive and a troublesome operation 

 to fill balloons, even when they were of small size 

 and intended only for amusing experiments. Now, 

 however, that in almost every town coal gas is manu- 

 factured, the filling of balloons either for aeronautical 

 ascents, or for the purposes of amusement, has become 

 very easy. The gas obtained from coal is sufficiently 

 light to make a balloon, filled with it, rise with a 

 considerable ascensive power. The specific gravity of 

 coal gas varies from one-third to two- thirds of that of 

 atmospheric air ; but the gas obtained from oil varies 

 from two-thirds to nearly the same specific gravity at 

 atmospheric air, so that it is entirely unfit for aerostatic 

 purposes. 



One of the simplest and most beautiful experiments 

 in aerostation is to take a turkey's maw or stomach, 

 properly prepared, t and to fill it either with pure hy- 

 drogen gas, or the carburetted hydrogen produced from 

 coal. If it is allowed to escape in the open air it will 

 ascend rapidly in the atmosphere; but the best method 

 of showing the experiment is to let it off in a high 

 staircase, and observe it ascend to the cupola, where it 

 will remain near the highest point till the escape of 

 the gas allows it to descend. 



Small balloons, either for rising with rarefied air, or Sm*ll bal 

 with hydrogen gas, may be made by pasting together loons, 

 gores of lawn paper cut out as shown in Fig. 5. c f 

 Plate III. of AERONAUTICS. If they are intended for 

 rarefied air, their lower ends must be pasted round a 

 slender hoop, from which proceed several wires ter- 

 minating in a kind of basket sufficiently strong to sup- 

 port a sponge dipped in strong spirits of wine. When 

 the spirits are set on fire their combustion will produce 

 a much greater degree of heat than any ordinary flame, 

 and by thus rarefying the air within the balloon will 

 enable it to rise with great rapidity and to a very con- 

 siderable height. 



If the balloon is to be filled with hydrogen gas, the 

 paper should be well varnished ; the lower end of the 

 gores should terminate by being pasted round a small 

 tube sufficient for admitting the gas, and capable of 

 being completely closed after the gas is introduced. 

 When the balloon is filled it will then rise with facility 

 in the atmosphere. 



The new varnish invented by Charles Mackintosh 



* We understood that the melodion which we saw at Geneva consisted of a number of steel tubes of different lengths and bcier, 

 f These ate to be purchased in Ixmdon fur about tour or fire shillings each, 



