Class X.] DIVIDING MACHINES, BY ACKLAND, FEliHEAUX, FROMENT, Ac.

supported at every point throughout its length; the bar is jcovered with a coating of gold-beater’s skin to defend itfrom attack by the mercury. It is probable that the !former is the better method, as the latter, though good in :theory, is probably not good in practice, from the fact that jiron rusts easily in mercury, and copper and its alloys icombine easily with it.

Mr. Simms also exhibits two standard scales, whichhave been used for the formation of many scales now inuse. They were made by the exhibitor, whose propertythey are. The tubular scale is No. 3 of Mr. Bailey’sReport on Standard Measures.*

Dividing Machines.

Acki.and (No. 3G8, p. 450) has exhibited a machine fordividing hydrometers and other variable scales, withaccuracy. The instrument is furnished with a mountedhead, screw, and suitable cutting apparatus.

The usual means of graduating hygrometers is bydetermining three points by means of three differentfluids, whose specific gravities are known, and dividingthe intervals between these points into equal parts. Thismethod is evidently defective, as the divisions, instead ofbeing equal, increase, in a given ratio from belowupwards.

The plan adopted by Mr. Ackland may be divided intothree processes:—

1st. The ascertaining the exact position of three ormore points of the scale, according as the stem of the hy-drometer is more or less cylindrical.

2 ndly. The dividing with great accuracy a scale onbox-wood, to show the specific gravities required to beindicated by the hydrometer, and to be used by the in-strument for the purpose of measuring and correctlymarking the distance of one division from another on thepaper scale with true mathematical certainty.

3ruly. The making a reduced copy of the box-woodscale, so as to form a scale, the points of which shall cor-respond with the distance between the ascertained pointsof the hydrometer bulb. The scale so formed on paper isthe scale for the hydrometer. For example, suppose it berequired for a hydrometer to show specific gravities fromrooo to 0‘700; to show this a bulb is chosen with a stemas uniform as possible, and three points, viz., *700, *850,and 1 * 000 , are ascertained as follows:—

Let a h c be the degrees required. Suppose m be thepoint on the stem ■whereon it is required to mark thehighest specific gravity, viz., 1*000 = a. To find thispoint, the instrument is loaded until it floats in distilledM ater at the temperature 62° Fabr., at the point m ; let theweight of the instrument then be x.

To find *850 = 6 .

Load the instrument until it weighs -where it floats

b

in distilled water, mark the tube at n.

To find *700 = c

Load the instrument until it weighs where it floats

e

in distilled water, mark the tube o.

Finally, before sealing the instrument, make it weighax; then mno will respectively represent the specificgravities required. By this plan, which M as suggested toMr. Ackland by Dr. Clark, of Aberdeen, the correctposition on the stem of the three specific gravities isobtained; the next and most important operation is thesubdivision of these spaces, so that each division shall be inits true position. This is done by copying a calculatedscale by aid of the machine, the construction of which issuch that a proportionate scale of any length less than theoriginal can very readily be produced.

The scale is determined by forming a table of thereciprocal of the specific gravities, and taking the differ-ences between them ; in use the micrometer head is suc-cessively advanced, and each division is cut with accuracyand with great rapidity.

Most of the scales of the hydrometers exhibited have

+ See the “ Transactions of the lloyal AstronomicalSociety.”

been graduated in the usual May, and are therefore in-accurate; those exhibited by Griflin (No. 457), were per-formed by this machine, which Mr. Ackland has the meritof inventing. He is the first in England who has carriedinto active practice a correct mode of subdividing glassvessels for gases and liquids by the aid of a machine.

The cutter is made to cut, and cuts a division. Thedetent, apparently, is then brought back to the commonCentre of the helix screw, either by lifting, unclamping,and re-clamping, or in some equivalent wav, and runs itscourse again to bring the cutter ready for another cut, andso on. There is also a second novelty, viz., a neat littlecontrivance to make every fifth division longer than therest by means of a -wheel which advances one step at eachdivision or movement of the cutter frame. A point, letdrop to touch its circumference, determines, by the depthto M-hieh it descends, the length of the cut; but at everyfifth step the -wheel has a notch into which the pointdescends, allowing the cutter to make a longer stroke—longer by the depth of the notch.

A Prize Medal was awarded to Mr. Ackland.

Perueaux (France , No. 369) has exhibited a straightline divider. This is a beautifully-contrived divideron Kamsden’s principle, with a long fine steel screw.The novelties are, first, the wheel at the screw head,which is divided into 400 parts, and has cut upon itscircumference (which is made broad), a helix screw, inthe thread of which runs a detent carried along by therun of the thread till it meets a stop clamped on thehelix at a definite point. This arrests the screw, at thispoint of the motion. A Prize Medal Mas awarded toM. Perreaux.

Froment (France , No. 1609, p. 1254,) exhibits adivided metre, the divisions on which are beautifully dis-tinct, and as far as could be ascertained, very exact. It isbelieved that the divisions were cut by M. Froment’sdividing engine, which he lias constructed for dividingastronomical and geodetieal instruments. M. Fromenthas also constructed a screw more than a metre in length,for the purpose of dividing lines quickly, and it is under-stood that in so doing electricity is made use of in con-nection with the movements of the screw and machine.

A Council Medal Mas awarded to M. Froment.

The Conservatoire i>es Arts et Metiers (France ,No. 1568, pp. 1251, 1252,) exhibits a brass metre byGuinbey, decimally divided. Also a fine platina metre,which is described as the “ second type of the Collectionof Weights and Measures of the Conservatoire des Arts etMetiers, —executed by M. Brurmen, and compared byM. Silbermann,” and is stated to be a copy of the ancientplatina metre of the same collection, an immediate deriva-tive of the prototype in the archives of France , and to belonger than that, of which it is an immediate copy, by0*000019 millemetre.

It is properly speaking a “ metre h. bouts,” and is con-verted into one “ h traits” by attaching to each of itsextremities a supplementary piece of platina, separatedfrom the bar by a very thin lamina of gold, which appearsas a fine line of gold at the junction. It is supported on abed of bronze, to which it is attached firmly and by accu-rate adjustment at one end, whilst the other is left free toslide by expansion, thus converting the whole system intoa Borda’s pyrometer, the amount of relative expansionbeing read upon a scale, the value of whose points hasbeen derived from experiment by immersion in meltingice and boiling water.

The Conservatoire des Arts et Metiers also exhibits astandard kilogramme and litre: a series of French coinsof legal currency, and a collection of wood measuringrods, both in single lengths, and in more or less numerousjoints; also measuring chains, and a series of measures ofcapacity of the following values (in litres), viz.:—

20 , 10 , 2 , 1 , J, 4 ,L, ,§ 3 , ^ s lj, in brass, iritli groundrims and sliding glasses to each.

Balances.

The Exhibition contains balances of all sizes, fromMr. Fox’s balance, intended to carry extremely smallweights, up to the balances of L. Oertling and theAmerican balance, both of which are capable of carrying