Cl.ASs X.

VARIOUS BAROMETERS—THERMOMETERS BY SIMMS, NEGRETTI, Ac.

001

tered, and from them both the readings of the barometerand thermometer are known.

Tiihmlktt (No. 103, p. 420) has exhibited amarinebarometer in a metal frame, with thermometer, enamelledscales and springs to check oscillation.

Eli.tott and Sons (No. 320, pp. 443, 444) exhibit ba-rometers carved in walnut-wood, the design representingthe four seasons; circular caned wood barometers simi-larly ornamented; Gothic carved barometers, and twomounted in ebony and gold. It is stated that the mer-cury in the tubes of all these instruments has beenboiled.

Bursill (No. 073a, p. 468*) has exhibited a compen-satory cistern barometer, in which, by a self-acting con-trivance, the mercury is always preserved upon the samelevel within the cistern, uninfluenced by alteration of tem-perature or any change in the column of mercury itself.

Brown (No. 670a, p. 408*) exhibits a barometer in ap-pearance similar to a water-barometer; it contains twoimmiscible liquids of nearly equal specific gravities; andtheir point of meeting, which may be placed at any partof the scale, is indicated by one liquid being coloured.The scale of the instrument, which is arbitrary, is 7^feet to an inch of mercury.

Mr. Brown also exhibits two barometers at an exceed-ingly low price. The readings of a similar barometerwere taken for two months commencing from July 15,simultaneously with those of a standard barometer, andwas found to act admirably. Before reading it wasalways found necessary to incline the instrument untilthe mercury filled the upper portion of the tube : it after-wards descended to its proper level, though the rise at alltimes took place less freely on account of the smallnessof the tube. These barometers are the cheapest in theExhibition, and are better than any of the ordinary baro-meters exhibited.

Bennett (No. 1 , p. 406) exhibits barometers of an or-dinary construction.

Dixey (No. 271, p. 43S) has exhibited a carved oakbarometer, and an ordinary barometer.

Baker (No. GIG, p. 452) lias exhibited two barometers,one of which is that invented by Mr. Brown.

Watkins and IIii.e (No. 659, p. 460*) have exhibitedbarometers of various ordinary kinds, and Professor

Potter’s aerometric balance.

Grey and Keen (No. 138, p. 422) have exhibitedwheel barometers mounted according to various designs.

Abraham (No. 140, p. 422) lias exhibited a barometer,designed to show, without adjustment, the reading of thebarometer. The scale is suspended over a pulley, bymeans of a counterpoise, the lower end of the scale beingconnected to a float in the shorter leg of the syphon.

A. II. Boss (No. 157, p. 429) has exhibited a self-com-pensating barometer.

Pizzala (No. 162, p. 429) has exhibited a wheel baro-meter, constructed with a rack-work motion. The caseis elaborately carved in walnut-wood.

Gkimoi.di (No. 159, p. 429) has exhibited a pedimentbarometer, fitted up in a carved gilt frame.

Bourdon (France , No. 1108, p. 1231) has exhibitedseveral barometers of an original construction. Theyconsist of an elastic flattened tube of metal, exhaustedcompletely of air, and bent very nearly in the form of acircle; they are in this state possessed of the property ofexpanding, a further separation of the ends being effectedwhen the atmospheric pressure is diminished, a contraryor contracting effect taking place when the pressure in-creases. A lever is attached to the end of the tube bysuitable mechanism, and connected to an index or hand,which traverses a divided dial-plate.

The dial-plate is graduated by placing the instrumentwith a standard barometer within the receiver of an air-pump, and tlie points of coincidence determined by vary-ing the pressure. These instruments are applicable formeasuring the pressure of the atmosphere, gas, &c., to a ‘range exceeding 500 lbs. on the square inch. They are ;well adipted for application to steam engines, &c. A ICouncil Medal was awarded to M. Bourdon. j

Galy Cazalat (France , No. 1239, pp. 123G, 1237) has jexhibited a manometer. The tension of steam is mea- j

sured by the number of atmospheres to which its pressureis equivalent, consequently, by the number of inchesof mercury which it will support in a tube by pres-sure on the surface of a reservoir into which the tubeis plunged. The utility of a mercurial gauge is limitedin practice by the length of tube capable of being applied,which, if of glass, cannot be safely extended, and if ofiron, is very inconvenient, to say nothing of the difficultyof reading. The invention of M. Galy Cazalet is ineffect equivalent to increasing in any given ratio the spe-cific gravity of the mercurial column, supported so as toenable a column of any convenient length to counterbalancea pressure, however great. The steam acts only on thesectional area of the rod of a piston, the plunger of which,of much greater sectional area, presses on and so sustains,in the other leg of the inverted syphon, into which itplunges, a mercurial column of sectional area equal to itsown. A Prize Medal was awarded to M. Galy Cazalet.

Ericsson (United States , No. 146, p. 1442) has exhi-bited an alarm barometer. This instrument is intendedchiefly for use on ship-board, and is to be placed in thevicinity of the helmsman, being so constructed that,when the mercury sinks below a certain reading, a ham-mer is made to strike a gong. The helmsman by thismeans receives notice of the probable approach of roughweather, and time is afforded for the necessary precau-tions of taking in sails, &c.

The tube is similar to that of the common barometer,and is much enlarged at the upper end; the lower extre-mity terminates in a cup, which contains mercury, andis attached to a lever, weighted at one end. By meansof the enlargement of the tube, a slight decrease in thereading of the barometer causes a considerable dischargeof mercury into the cup, the balance of which is dis-turbed. This disengages a hammer, winch, impelled bya spring, strikes a gong with considerable force. Theweight which balances the cup is adjustable upon thelever, and may be so set that notice shall be given of anyrequired reading of the barometer. The lever is markedwith divisions corresponding to those on the scale, forthe purpose of adjustment.

Thermometers.

Simms (No. 741, p. 475*) exhibits two standard ther-mometers, constructed by the Rev. R. Sheepshanks, who,during the last two or three years, has been more or lessengaged in improving these instruments. The divisionsare engraved on the stems. The zeros of these instru-ments, as determined by Mr. Sheepshanks, will be usedby Mr. Glaisher in all future observations, and he believesthe two instruments, exhibited by Mr. Simms, to be themost correct in the country.

Xegrktti and Zambra (No. 160a, p. 429) exhibit astandard thermometer, which seems to be good ; severalvery delicate thermometers, with pea bulbs; a delicate dryand'wet bulb thermometer; a Daniell’s hygrometer; twoKegnault’s hygrometers, one furnished with black glasscups, instead of silver, designed to avoid oxidation ; somethermometers beautifully made, and graduated on theirown stems ; a dry and wet bulb, with two identical stemsclose to each other, and united; this form of instrumentis useless for practical purposes, but is a masterpiece oftube-blowing; several self-registering thermometers, bothof Rutherford’s and Sixe’s form, &c.

These are the only Exhibitors in the British portionwho have sent thermometers with their stems graduated,the only safe instruments for delicate experiments.

A Prize Medal -was awarded for the beautiful workshown by these artists.

Newman (No. G74, p. 468*) exhibits a standard ther-mometer, the bore of which is stated to be a perfectcvlinder, having been examined by the late CaptainKator and Professor Daniell, as well as by Colonel Sabim*.Its scale is divided into half degrees; that part of theglass tube which is near the scale is ground flat, ami po-lished, so that the column of mercury is very ncarh inthe same plane as the scale, by -which means the error ofreading, so far as parallax is concerned, is avoided.Also, a maximum register thermometer, with a smallpiece of enamel inserted between the index and the mer-