Class X.]
ACOUSTIC INSTRUMENTS AND TLANIMETEES.
303
is illuminated at night, andean be seen at a great distanceat all times.
The instrument is elegant in appearance, and seems tobe perfect in its action, and is the only one which showstime and tide by separate dials. A Prize Medal wasawarded to Mr. Uewitson.
Nkwmas (No. 674, p. 468*) has exhibited a self-regis-tering tide-guage. This instrument consists of a metalcylinder 30 inches in length and 8 inches in diameter,moved by a clock, and performing one revolution in 24hours. A peucil moved by a float is suspended by anendless chain, and maintains always the same buoyancy.The peucil attached to the chain is carried over twocylinders, one of which contains a spiral spring, and is socontrived, that the marking of the change of tide is im-mediate. On the face of the clock is shown the height ofthe tide at the time of observation. It also registers thehighest and lowest for the day. The papers requirereplacing every fortnight, and the pencils used aremetallic.
The chain consists of a given number of links, the endsof which are not soldered together, which in its progressloops over the spikes in the barrel; this method will dowell for a time; but as the links cannot keep all of thesame length, it is probable that some will not catch, butslip past, and cause error in the register
Helps (No. 615, p. 476) exhibits a pulpit, to the read-ing-desk of which is attached a receptacle for collectingsound, to which a gutta-percha tubing is connected, in-tended to be carried under the floor, or otherwise, to thepew of the deaf person; the terminal of the tube, which isintended to be applied to the ear, is of ivory.
Rein (No. 629, p. 477) has exhibited several instru-ments for acoustic purposes; one of these may be wornwithout being seen, is adapted to the shape of the ear, andrequires no spring. The power is great in proportion toits small size, the entire length of tube being 8 inches.
Another acoustic contrivance, which may be worn as alady’s head-dress, without being seen.
Also a new promoter of hearing. The great fault ininstruments of this class has hitherto been the concentra-tion of the sound in one ear only; so that, whilst thesound was much increased in loudness, it remained, ifpossible, still more confused and indistinct. To obviatethis inconvenience, Mr. Rein designed this contrivance,which is to be worn on the head, and is adapted to bothcars: by means of it the faulty ear is called into equalaction with the healthy one. "When worn by ladies, itmay be quite concealed by the hair.
An acoustic chair. This is so constructed that itspower by reflection is doubled to either ear, and may beused at pleasure for one or both ears. In the latter casethe power is fourfold. The chair is rendered acoustic bythe arms being made hollow, and terminated by a designsuitable to the free admission of sound, which is conductedto the ears of its occupant, by two small tubes, projectingfrom the inner side of the back of the chair.
An acoustic vase, designed by its construction to collectthe sound from all parts of the room. The vase beingplaced on a small table, the attachment of the tube isskilfully concealed beneath the table through which it isinserted; contrary to other contrivances for the same pur-pose, it is not trumpet-shaped, and in its appearance doesnot resemble an acoustic instrument.
All acoustic instruments hitherto made, partake more orless of the trumpet form; and all agree in one respect,viz., that the mouth or orifice for the reception of soimd,is bounded by a line, generally circular, every point ofwhich is in one plane; and, therefore, it is necessary thatthe voice of the speaker should be directed as nearly aspossible at right angles to this plane. Some instrumentshave been made consisting of a large metallic receptaclefor the sound, with a long flexible tube attached to them;but they are very unsightly objects. The vase above de-scribed differs from these in the following particulars:—
1st. That the orifice for the collection of sounds isarranged on a circular plan, so that when the instrument Iis placed on a table in the centre of a room, the deaf per-
son can hear speakers in any direction with distinctnessproportionate to his degree of deafness, or the tone ofvoice used by the speaker.
2nd. That it has not the appearance of being anacoustic instrument.
3rd. That it may be used as a flower vase. It is ofcourse furnished with a flexible tube for the purpose ofconveying the sound from the vase to the ear,
Mr. Rein has exhibited more than one design of theacoustic vase, several acoustic bells, also an acousticwalking-stick, which may be applied to either ear, with-out being recognized as an acoustic instrument.
Several portable telescopes, adapted to various degreesof deafness.
An acoustic instrument, or “ Social Companion,” toenable any number of persons to converse with one who isdeaf, and requiring no change of place.
A conical and flexible whispering tube, so constructedthat extremely deaf persons can distinctly hear and holdconversation even when spoken to in a low tone of voice.
A whispering tube, and ear-caps or reflectors, whichlast may be worn without a spring.
Watkins and Hill (No. 659, p. 466*) exhibit asyrene; an instrument used in acoustics for demonstratingthe production of a musical sound by a succession ofmusical impulses. The invention of M. Cagniart De LaTour,
Planimcters.
Sang (No. 33S, p. 448) has exhibited a planimeter.The peculiarity of the construction consists in the productof the ordinating lines being given by the motion of adisc over the surface of a cone, instead of over a plane, bywhich means, the motions representing both the ordinatesmay be taken directly from the motion of the tracingpoint. In the Tuscan instrument the motion which re-presents one of the ordinates is conveyed through a rackand pinion, and in those of Swiss and German construc-tion, through a hand and pulley. The arrangement ofMr. Sang is designed to obviate the shake necessarilyeaused by the teeth of the rack, and by the elasticity ofthe baud of the pulley.
The parallelism of the instrument is trusted entirely tothe simple rolling of two heavy wheels over the paper.This is rendered more certain in the foreign instrumentsby the rollers working in guides as on a railway. All,however, appear free from any tendency to divergence inthis respect.
Mr. Sang’s instrument possesses a practical advantagein the readiness with which it may be placed at once on adrawing of any size.
The error contained in the results given by instrumentsof this class generally arises from the shaking or elasticityof the parts which connect the index with the tracer.This error in practice may be easily corrected by mea-suring the figure twice; at one time placing it so that theshortest breadth is represented by one of the motions, andat another, so that the longest breadth is represented bythe same motion. The average of the two results will bevery nearly the truth. The Jury considered Mr. Sang aswell deserving Honourable Mention.
Gonella (Tuscany , No. 70, p. 1298) has exhibited aplanimeter. All, or very nearly all, the planimeters, ofwhich the Exhibition contains several, turn upon the me-chanical integration of the differential expression for thearea of a curve traced on a plane surface, and are mostreadily conceived on that old and now almost forgottenview' of the differential calculus, which regarded the dif-ferential of a magnitude as a measure of the velocity ofits increase at any instant. Suppose a straight line to becarried with a uniform motion along the base line (orabscissa as it is termed), of any curvilinear area, remain-ing always parallel to itself and perpendicular to the baseline; and that, during this motion, a moveable point inthe line so carried is kept always on the circumference orboundary line of the area. Then it is clear that the velo-city of increase of the area will be proportional to andtherefore measured by the length of the ordinate, or pointof the moveable line'included between tlie base line anddescribing point.