146 J+OJNWX! S’tandarcE of Measure and Weigh/.

varies in density from many causes, anti has, therefore, never been considered applicable to the establishitq Of a standard.

Rly object is to l1rl)pW5e the meitns , at all times and places, of pro- curing a pal*Liat atmospfwe Whose density shall always he the same; and to depend On t+ ~l~~sfiCif?/ Of this partial atmosphere fur the sup- port of a column ol mercury (of the uniform density,) at the same height. ‘lb lerq,th of this column to he taken as a .sta~Za~l of meu- sure-suhjcct, hoWever, to tllc necessary equations, which \vili be hereafter mentioned.

For the purpose of pursuin g this inquiry csperimcntally, an air pump. and condensing apparatus, With SUitilblt? glass receivers of pro- per dimensions ant1 strength; also, gold a11d mercury of the estahlish- cd relative densities, an accurately atljustcd Of suitable Icngth, will be required.

balance, and a glass tube

The articles mentioned being at hand, proceed it1 the following manner. Let any accurate cube Of gold Of the established relative density be made, of which ICt the line A I3 represent the side.

A I3 ---_

Wow let a hollow glass cube be accurately made, whose side shall be ten times A I& (or, any other established multiple of A I&)

The gold and ~OIIOW glass cubes must esactly balance in yacuo, (This glass cube we will call C.)

Let a go111 weight be now made, of an! shape which shall be ex- actly equal to one lluntlredth or one thousandth, or any other esta- blished proportion of the gold cube A IS, by weight, (and call it D.)

In the annexed cut, M N is a receiver of glass, K, a forcing pump. I? G, an accurate balance. L, a thermometer. A R, the gold cube. C, the glass cube. D, the small gold weight. I3 I, the glass tube, the lower end

immersed in mercury. This tube should be filled to the

common height of the barometer in the same way that barometers are filled, Ieaving the space above a perfect va- cuuin.

Before the forciog pump is applied, the glass cube will preponderate, on account of the addition of the small weight D.

The air must now be condensed by means of the pump K, until the ba-

lance is accurately restored, which will take place in consequence of the less specific gravity of the glass cube, and then we shall have the insulated or partial atnaosphere proposed.

Proy_msed Slnndurd of il4ecrszcre nm? #4&g&. 147

The height of the mercury in the tube must now be ascertained at 3.

Thus whatever Cube Of gold is first aSSUmed, if me keep up the samC relative prOpOrtiOnS t~~rOlighOUt, We Ski\] always obtain a partial

atmosphere of the same abjc>lute density, and \vhose elasticity will consequently be the same, and hence capable of supporting the Same

column of mercury of the same density. A standard formed O!I the foregoing principles, zc,$! carly, First, in different latltudcs, nom the variation of gravity. Secondly, In the same latitude, from the same cause, and on ac-

coulltaf dilkrcnt elevations above the level of tl~e sea. And it may vary, Thirdly, on account Of the gravitating power of the moon. Fourtltly, it may vary, fr(!m diftcrerlt states of electricity pervad-

ing the atmosphere and pOss2@/ aff’ccting the elasticity of our partial atmosphere.

‘I’llese are tire Only CUUSeS, Of which 1 am aware, that can possibly

afltct our standard. The two first are real, and must be equated; the last are imaginary, but may be examined.

I would propose, that a standard obtained by the means mentioned, at the equ3tor, and On the lCVe1 Of the ocean, should be esteemed a U,k;ersnl Stcl~lu~~~ qf MCWUW, which standard is susceptible of ac- curate calculation, wthout experimenting at the place, as the experi_ ment of any latitude can bc justly equated to any other latitude; for this purpose a table of corrections sllould be constructed which might extend to every minute of latitude.

I am not critically conversant in calculations of this nature, which may be left for the qualifictl mathematician.

Our ex~~erinzenlul stanilarrl kin, (p corrected for the latitude, may be called an npproxinzate standard, and will be sufficiently near the truth to lay the foundation of calculations for further corrections on account of the different elevations at which the experiment may have been made, which needs no exp!anation.

The next inquiry is, what influence will the moon have on our

mercurial standard? On first view, Ii was led to believe that this infiuence would be con-

siderable, seeing that the mercury is supported in the tube by the dustic spring uf air, and sot by a superincumbent column of the at- mosphere acting by its gravity. Calculation, however, convinces me that this influence must be inconsiderable.

The mean distance of the moon from the centre of the earth is 1,2F7,200,000 feet? or about sixty semidiameters of the earth. Also the force ofgravitp at digwent distances, is inversely as the squares of the distatkcs. *

The radius of the earth is 21,000,000 feet ; therefore, as the square of 1,267,200,000 is to the square of 21,OOO,OOO, so is the force of grrvitg at the surface of the earth, to the force of gravity at the dis- tanceof the moon, viz:-

~,605,79~~84o,ooo,o~o,ooo : 441,000,000,000,000 : : 1 : 0,000274;

1148 Proposed Standard of Measure and WeighE.

sO tllat the force of gravity at the surface of the earth, is to the force

Of gravity at the nlOOn, as 1 is to 0.000274; or, as l,OOO,OOO to 274, The magnitutle of spherical bodies is 8~ the cubes of their radii; hut the mean radius OF the moon is to the mean radius of the earth near_ ly as 3 : 11, and 3” : 113 : : 1 : 49 nearly. earth being nearly 49 times that of the moon.

The magnitude of the

Tile attractive force at equal distances is aS the quantity of matter, but the attractive force Of the Garth at the In000 is represented by O.OOO5374, consequently lbe attractive force of the moon at tile earth \vill be one-forty-ninth of O.OOO274, or O.OOOO05G.

‘rhus far I have consi~lered the earth and moon of the same (len_ sity; but the quantities of matter are a8 the densities, the bulk beinn the same; and the density of the earth is to the density of tile nloo~ as 48 to 5;. IIence as the dcnslty oft!Je earth 4; is to the tleosity of ille moon 52, so is the attractive force of the moon 0.0000056 to her true attractive force, viz. 4.5 : 5.5 : : O~OOOOUS(i : O.OOUOOG~. ‘rllat is, the attractive force of the moon exerted on botlies on the earth’s sup_ face, anlourjts to 1-i,06$aiia of the force of gravity on the e&Ii’s sup_ face; in other words, it would e\CVate the COlU0lll Of mercury in tube iiia.~gSoB of the whole column.

If this force had been greater, it WOUld have been necessary to equate it, to suit Iiot only the latitude Of the place of Csperirnent, but also to suit tbe latitude of the moon.

In the laupngc of Kicholsori, “Newton calculated the cft&t of the sun’s iu!luence in tl~is case, (the titles,) and found it about three times less than that of the moon.” This language H consider equivocal. But in the case of our stsotlartl, to place the sun and moo0 as much as possible out of harm’s way, let ull our experiments be matIe when both these luminaries are on the meridian.

The nest subject is, what will be the effeCt of electricity? Here analogy will furnish but little light, it will have to be referred to fu- ture experiment. There is,. however, a furtbcr consideration which I. have intentionally avoitleil, I mean the moisluye q[ air, which would materially afI’cct all experiments clepending on the elasticity of air. Now to rfnder as few instruments of observation necessary as possi- ble, L propose to clispse with the hygrometer, believmg that in its most perfect construction, it is subject to much error; anrl on this ac- count let the atmospheric air, to be used in experiment, be al\vays rendered as dry as possible, by kecpin g it for some days in close ves- sels, over a IaFge quantity of quick lime. And now to return to the electricity; this fact we do know, that tlle,electric states of’the utmo- sphere are much inf:uCncCd by the quantity of moisture which it may contain, but as we shall always use it in its most dry state, we shall probably have it free from danger, from the eKxts of electric inilu- ence.

Gene& Observntions.

A standard of measure being thus established, there is no tlifficultj’

in determining from it a standard of weight; the principle is altogether

fleinvenlion of Hare’s Compound Mow-pipe. 149

con&tent with the foregoin,, m and is too well known to require expla-

nation. on the subject of the absolute length of the standard of measure, 1

have ventured no oprn1o.n; the prtnciples proposed being general, may, by o&~in~ the rehtrons, produce various lengths.

7u common parlance, a p ressure ot about two atmospheres, would produce a standard ot about five feet, which I should suppose a very suitabIe length, and conventently adapted to the prrnciples of the ex- perimetlt.

One observation more? and I close the subject. A glass cube, of the !lZe apprOpriate for this experiment, (as it must

be hollow, and its magnltU(le plot ieSS than 1000 times that of the gold cube,) would, on account of its shape, be badly calculated to resist the pressure of a single atmosphere.

‘ro obviate this difhculty; let a cube be made of any hard substance, and of the proper size. Then take a vessel of suitable size, open at top, iat0 which pour mercury 7, or water, until it stands at any )reig[lt; then immerse the cube altogether in the fluid and mark the hejgljt, withdraa the cube, and immerse another glass vessel (bottle shaped) until the mercury stands at the last mark, and also somewhere on the neck of the bottle; now let the neck of the bottle be cut otf where the mercury marks, this bottle shaped vessel will of course be the same size as the cube, it must balance the gold cube, which lnay be efftcted by throwing into it any substance, and then closing it herme- tically, to be used In place of the cube of glass.

Reinvention of HaTe’s Compoetntl Blaw.pipe.

GENTLE:WEN ,-In looking over a recent number (No. 6, third se_ ries, December, 1832,) of the b “ London and Edinburgh Philosophi- cal Jlagazine and Journal of Science, ” I was struck with a para- graph, in which Mr. J. 0. N. Rutter claims to have inz;nroverl Ckrrke’s blozo-&e, by placing the oxygen and hydrogen gases in separate re- servoirs, and allocvlng them to unite at the orifice of the blow-pipe: in other words, he h;ls ~~t~erzletl IIure’s Oh-pipe as a)z improve- ment upon Lilularlce’s. the paragraph in full.

That there may be no misapprehension, 1 give

is Notice of a new Oxy-lylrogen Blow-pipe .!Jppnm~~s. By .J. 0. LV. AWer.”

“ 1 have caused to be constructed by Mcssrs IV. & S. Jones, 30 Dolborn, an apparatus which is more simple, and at the same time alore elective than either Clarke’s or Gurney’s blow-pipe; and it possesses the additional atlvantage of being:~erjkctZg safe. The most