MR. TOMLINSON'S MANUAL OF NATURAL PHILOSOPHY. Ie any person of
active pursuits is at a loss to employ his spare time, or if any idler, with a mind not utterly unfitted for
intellectual attention, is weary of his profitless life, let him pur- chase Mr. TostststsoN's Manual. To the contemplative it will afford a fund of curious and interesting knowledge, exhibited by means of instruments, found in almost every house, and illustrat- ing the natural laws by which we live, or enjoy life. To the speculative it will afford ample food for speculation on the nature and properties of some of the most recondite and subtile 'processes continually going on around us, continually affecting us, and yet
constantly baffling us in their final causes or modi operandi. To those who combine curiosity with patient industry, and who wish to know surely what they do know, the Student's Manual of Natural Philosophy will set them in the way of putting nature to the question, by a series of experiments on a variety of sub- jects, conducted with simplicity, ease, and cheapness.
The reader will understand that Mr. Tostusfsosis work is not an original treatise : on the contrary, its object is to popularize
discoveries shrouded in volumes mysterious to the world; but so to popularize them that he shall avoid " the extremes of the merely popular and the strictly mathematical. The plan, how- ever, is original ; and it cannot be caled a compilation even as re- gards its matter. Apparently a teacher of natural philo-ophy, Mr. TOMLINSON has mastered his subjects without a view to book-writing : he has repeated, tested, varied, and extended the experiments connected w ith them, and thus made the knowledge his own before he attempted to impart it to others. This training, too, has given an original cast and freedom to his manner; which is admirably expositional. With much of earnestness, arid at the same time of ease, he unites great clearness, and has hit the difficult medium between a wearying diffuseness and a tasking brevity.
The subjects discussed are a dozen. The Thermometer intro- duces heat ; the Barometer, the atmosphere ; the Hydrometer, waters; and the Hygrometer, vapours. The history and explana- tion of the little instrument called the Vernier, or Noniva, in- volves the measurement of surfaces, and admits an episodical account of weights and measures. The Compass, besides the pro- perties of the magnet,the uses of the needle, and the philosophical results which have been deduced from its observation, serves as a peg for a sketch of its history. The chapters on the Tuning Fork and on Musical Glasses, give rise to an account of the theory of sound ; an interesting exposition of its general nature, and a curious description of a series of elaborate experiments on musical sounds. The Prism enables the author to treat of light, the Te- lescope of optics, each involving the discoveries of la:km-sox; colour, repulsion, and several other subjects, are begot upon a Soap Bubble; and the Sun Dial involves the construction of that instrument, the laws upon which it is based, and a history of time-measuring.
The book, to be appreciated, requires to be read throughout, ia one of its sections at least. All that independent selections can do, will be to convey an idea of the author's manner ; and not always of that very advantageously, because they must of neces- sity come from episodical parts. The chapter likely to be the most generally interesting from its subject, is that on Musical Sounds ; but, requiring much space for developing the leading principles of acoustics, and involving in some of its parts arith- metical calculations, we must confine ourselves to incidental passages. Here, in the philosopher's fiddle, is a hint when should set all instrument-makers on the alert. The number of musical sounds we have every reason to believe is limited ; but what limit can be set to the beauty of their tone, if instruments were constructed on principles best adapted to develop their respective qualities?
SAVA ET'S VIOLIN.
The great object of this philosopher's reseirches was to determine what were the essential elements of the violin, and what were merely ornamental or em- pirical details. On considering the principle of the instrument, lie arrived at the opinion that the vaulted or curved form of the face and back is not a neces- sary part of the structure. In the caper imental violin which lie constructed, he employed 6 it surfaces uf very thin wood. The face and back were each formed of two pieces, similar and equal to each other,-21 lines thick atone edge, and gradually tapering towards the other edge, which was about 1 .me thick ; the thick edges of the two were then joined together. The next pecu- liarity which we may mention is, that the sides of the Instrument were straight instead of being fancifully curved, as in ordinary violins. The reason for this change was, that the sides might enter into undisturbed vibration from corner to corner of the instrument, and thus aid the sound, which is prevented in the common construction. The form of the instrument was that of a trapezium, or four-sided figure, of which the end near the handle was shorter than the remote end. There is, in common violins, a bar, called the bar of harmony, passing along the under surface of the face of the instrument, for the purpose of strengthening it. This bar is placed a little on one side of the middle line or axis of the instrument, and the soirnding-post, or soul, is placed at a short distance on the other side. Now this is a defective arrangement, as the bar stiffens, and retards the vibration of one side of the axis more than of the other. Savart, therefore, placed his bar of harmony along the central axis, and thus equalized the vibratory power on the two sides of it. The sounding-post has usually been considered as a kind of support for the upper surface, but Savart found that its only effect was to connuunicate the vibrations from the face to the back of insti want, and the point at which he fixed the post in his violin was such as to convey the sonorous vibrations more perfectly and energetically from the face to the back of the instrument. An unprovent was next tuade in the perforations of the face of the instrument. Savart covered the two holes on the face of a violin with paper, and found that the sound was very materially injured thereby; this he attributed to the stop- page of communication between the air within the body of the instrument and the external air. Having thus determined what was the real office performed by these boles, he next directed his attention to the form in which they are generally made. This form represents an Italian 5; but Savart considered that the margin of such an aperture must necessarily be variously affected in its vibration, according as it coincided with, or was inclined to, the direction of the
fibres of the wood. He accor tingly made those openings in the form of a parallelogram, that is, the edges were straight and parallel. By this arrange- ment the fibres and the margins of the holes were in the same direction, and the vibrations of the wood at those parts were rendered more symmetrical, while at the same time fewer fibres were cut.
There can be no doubt that many parts of ordinary violins tend to damp rather than to improve the tonea. Accordingly, Savart took every precaution to insure cooperation in every part of his violin, as much as possible. Before the instrument was put together, be brought the tablets which were to form the face and back into precisely the same vibratory state; so that each one should yield the same sound, anti the same nodal distribution of sound on its surface, as the other. Ile conjectures that the old makers were cogn'zint of the importance of this adjustment. Here, then, we see in bow many ways Savart's violin differed from those or- dinarily constructed. 1st. The tablets were flat. Oa. They were thicker, and therefore stronger than the ordinary curved tablets ; their flat form rendering them capable of vibtating more readily. 3d. The bar of harmony was so placed as not to stiffen one.half of the face more than the other. 4th. The soul, or sounding•post, was place.' so as to convey the vibrations fi om the upper to the lower tablet more energetically. 5th. The sides of the instrument were made straight, so as to add, by their facility of vibration, to the souorous effect. 6th. The apertures in the upper tablet were straight instead of curved, so that, while they permitted communication between the internal and external air, they reso aided the general effect by the vibration of straight margins. These ',shag the general points of difference bt tween the common violin and that coast' iteted by Savart, the successor the attempt was soon put to is severe test. III. Lefebvre, the celebrated Parisian violinist. was r .quested to compare the tone of his best violin with Strait's. The result was, that the old one was found to have more brilliancy, but the new one more evenness of tone. Swett reniarks, that many of the best violins are more insensible to some notes than to others. This he attributes to the circumstance that, throuth the bail ad- justment of the bar, po-t, Ssc. the facility of vibrating in accordance with some notes is less thau with other,; whereas, in his own instrument, freedom and facility of vibration were provided for in every way. M'hen the old violin be- longing to Lefebvre and the new one of Savoie were played alternately in an ad- joining apai tonent, the tones of the two could not be distinguished front each other, except by a little more sweetness in the new one. This was ptobaably the first attempt to la duee tidille•making to scientific principles; and the success %illicit attendsel it oualw to encout age similar efforts. Savart made m iny violins such aar we have described, which bad no pretensions to elegance or high finish, but all possessing the desirable qualities which we are in the habit of attributing to the t, good old " violins. Should any of our readers be of a mechanical turn, they might construct goal violins at the cost of a few shillings, by attention to the main points of difference between the common instruments and those above &scribed ; all of which latter were made by Savart's own hands.
Previous page
