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uml several other elements are monads—that is, tliey have only one unit of chemical force; carbon, on the contrary, is a tetrad, or possesses four units of force: therefore carbon is only saturated, or its affinities satisfied, when it is in combination with four atoms of hydrogen. When two atoms of carbon are concerned, each atom exchangee an affinity; so that six units of force only remain to be saturate!. There exist other series in ■which two or more affinities of the carbon are exchanged; an instanco of snch grouping la to be found in the aromatic series of alcohols and hydrides. When a group of atoms exists which shows some degree of chemical force, then that grcup is termed a compound radical; and its eqniv-nleney depends upon the number of affinities which remain unsatisfied. Thus sulphur, which is an hexad, if combined with two atoms of oxygen, is partly satisfied, leaving only two units of force; SOa, then, is a compound radical of dyad equivalency.

The marks employed to represent the equivalence of an element or of a compound radical were proposed by Dr. Oiling, and are of great use. They consist of dashes or small Boman figures at the upper right-hand corners of the symbol?. In fie monads they are generally omitted, thongh in some instances they are used. Thus Г indicates monad iodine; 0', dyad oxygen; Au'", triad gold; CiT, tetrad carbon; Nv, pentad nitrogen; and ST|, liexad sulphur.

The elements do not always exhibit the same degree of chemical force. Thus, in hydrogen, sulphate sulphur is evidently an hexad; in several organic compounds it appears tctradic; whilst in t,he metallio eulphides it acts as a dyad. From this it appears that sulphur has more affinity for oxygen than for most other elements, for under certain conditions it will saturate itself with oxygen, one atom combining with threo of the latter.

Sodium has always been classed as a monad, but Wanklyn (Chem. A'etes, pp. 293 and 313, vol. xx.) tries to make it appear trivalent, a fact which, perhaps, will explain the constitution of some of the so-called double salts.

The equivalence of a radical is expressed by the same means ns for an element. The dyad radical ethylene may bo formulated thus (C-H,)", the two dashes showing its equivalency; (CSH5)" is the triad radical propylenyl, or glyceryl.

Those elements which exhibit an uneven equivalency, such as hydrogen, boron, gold, or nitrogen, ore called perissada; and those of even equivalency are termed artiods: specimens of this latter class aro to be louud in oxygen, carbon, and sulphur.

In graphic formula;, of which we shall speak farther on, the atom is demonstrated by a circle containing the initial letter of the element, its symbol; and the equivalence, or chemical force, by projecting lines, each line or connecting link being equal to one unit of chemical force, and generally termed one affinity.

Symbolic formula: may bo of several kinds:—
a. Empirical.
ß. Kational.
y. Typical.
S. Graphic.
«. Constitutional.

Empirical formula: .generally expresses the total number of atoms in the molecule. This is not any, or very little, inconvenience in inorganic chemistry; but when considering organic structure it should be very seldom used: in fact, the system espres-es only snch data as would lead to tlie calculation of the percentage composition ; it si ves no cluu whatever to the probable position of the atoms in the molecule Hydrogen sulphate is designated by the empirical formula H SO4. This dove uot tell us whether the oxygen is totally or only partially united with the sulphur; rational will tell us that. Again, the empirical formula for hydrogen orthosjlicate isHtSiO«; and hydrogen metueiKoate, IfjSiOj: this expresses nothing mnro than the number of atoms in the molecule. But there exists another kind of empirical formula. This modification is not much used in mineral chemistry; it is the formula gained by the ultímalo analysis of an organic compound. The same formula is gnined in the analysis of metallic salt», when the number of atoms in the molecule can be further divided. Thus cuprous chlorido may have an empirical fórmala of CuCI, which i< a, multiple of the real formula Capí,; hydrogen djthionate, LI.jS,Oe, would have an empirical forojula of HS03,' which is obwinod by calculation

Crom the porcentage composition, but as it ie a bibasic acid we know that it must contain two atoms of hydrogen, therefore the true formula is

a,s,o„.

In calculating the percentage composition from the Empirical formula, we proceed thus:—

H, = 2 162 parts of hydrogen dithionate

S, = 64 contain 2 of hydrogen, what will

Oc = 96 100 contain?

162 162 parts of the above contain 64

of sulphur, what will 100 contain? Estimate the oxygen by difference:—

100 x 2

= x, or amount of hydrogen.

162
100 X <u = y, or „ sulphur.

162 And

162 — (x + y) = oxygen.

On the other hand the empirical formula may be derived from the pc-centage composition thus: The percentage composition of calcium carbonate is:—

Calcium ...i ... 40

Carbon 12

Oxygen 48

100 These numbers, when divided by the atomic weights of the respective elements, give the empirical formula thus:—

40 -f- 40 = 1 of calcium, 12 -i- 12 = 1 of carbon, and

48 -r- 16 gives 3 of oxygen,

therefore the formula would be CaCOj.

Rational formula: gives us name clue to the constitution of a compound, but often this is very slight. It indicates the manner in which a compound is affected when brought under the influence of certain reagents, and as one compound is affected in various wars it is certain that thero must be several kinds of rational formula: for such a compound. Hydrogen orthosilicate may be formulated in either of the following :— H4(SiO»), SiO.,(II,0),, Siiv(HO)!; the first expresses the constitution on the binary theory'— four atoms of hydrogen being united to silicic radical SiO<, the second shows that it is a componnd of water with silicium dioxide, and the third that tetrad silicium is saturated with hydroyl.

The next on the list is Typical formula:. This formula; is used on the supposition that all bodies may be represented, and referred to substances of simple origin. There arc five distinct types, although some reckon only four; some, indeed, reckon more than five, but the excess may be referred to types of more simple origin, or condensed types.

The first, or hydrogen type, is called the molecular type, because Gerhardt placed under it the moiccules of the metals and compoun radicals

(Ag . (CN (C.H5

'(Ag • |CN '• '(cjh5

Hydrojjen. Iodine. Silver. Cyanogen. Allyl.

The hydrogen chloride type, commonly called the hydrochloric acid type, is ranked by some with the above; but it is a mixed type, or rather an intermediate stage between the molecules of the chlorous and basylous elements. Thus:—

( H (H (Cl

III ; I Cl ; t CI

Chlorides, iodides, bromides, and fluorides are represented on this type, and the polybaloid combinations are represented on what are termed condensed molecuks :-*

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The above are specimens of compounds arranged on the water type, whicb, though admirably suited to inorganic chemistry, is not .«nfficiently explioit when applied to bodies of organic origin; for instanoe, hydrogen oxalate is expressed :—

(«gr(0|

This does not give us its proper constitution, as the group (CjOj) exists divided in the molecule, partly saturated with hydroxyl, in the form of oxatyl or carboxyl; the constitution, then, would be ( CO-HO

\ CO-HO

This water type is made to embrace a large number of bodies, as by its means is demonstrated the constitution of all acids and oxides, Wanklyn, however, objects to this on the grounds that such a powerful base as potash can never be formed from such a neutral compound as water. This view may be correct, but in potash we have a much more basylous radical than the hydrogen in water; in fact, the hydrogen in water is brought by Odling very near the chlorous elements, as in several places in his Practical ÇhtmUtry he writes water as hydric acid. According to Wanklyn's views, the affinities of the oxygen in potassoxyl, &c, are completely satisfied, that wuieh holds it on to the chlorous radical being the affinity of the potassium, which is thereby saturated.

By giving most of the monad metals and metalloids a triadic signification, we are able to assign a definite formula: for most of the double salts, which before had no form of classification A simple substance is under our notice at oucc, and one which is very familiar—alum. This is a double salt, formerly regarded as a combination of two sulphates, and culled the double .mlphatr 0/ aluminium and pirtasxium. However, there is a chloride very similar in its properties, aud there is no doubt th:it there is a family likeness. We nnv represent the chloride:— К Л '»' К \ HU

AlCC"; and the sulphate £1.-(SO»)i

к; к )

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ON THE

And silver must not be excluded, the sub—or argentous—chloride, instead of being looked upon with doubt, must be regarded as a definite compound, in which the affinities of the silver are tightly held together, so that the molecule cosily The followiug would be

:TSr.n.aS«.g the yields metallic silver The followiug M^aKamc ammonium:'- the graphic formula for this compound

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hydrate of an organic ammonium

Huo , H »

H ) J^l ',

Ammonium bydrate. Teirethyl ammonium

hydrate.

The utility of this ammonium formula does not stop here, for by its means we may indicate the composition of the so-calle* metallammoniums, as euprammemium sulphate and platotatnmonium chloride ;

R)

Ho )

Platosammonium chloride.

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Cuprammoninm sulphate The last type we will consider is the marsh gas type. By its means we can demonstrate the constitution of nearly the whole class of organic bodies. By starting with marsh gas we can, by the substitution of methyl for hydrogen, pass up the series to those members of the group which contain many carbon atoms.

It we take an atom of hydrogen from marsh gas and replace it by the methyl radical, wc pass to the next in the series—ethyl hydride j and if we replace another atom of hydrogen by hydroxy), we pass from an hydrocarbon to an alcohol. Again, by abstracting hydrogen we can form aldehydes; and by adding oxygen to the latter, we form acids. All these changes can be represented by the employment of formulae on the marsh gas type:—

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HO ,
Ethyl Ethyl
alcohol, aldehyde.

Graphic formula; are seldom scon in any textbook on elementary chemistry, but specimens are jriren in Miller's Element* Vol. III.; Frankland's Lecture Notet for Chemical Student*; and in Buckmaster's/'toryaHJc Chemistry. Thisspecies of formula: is utterly ignored by some chemists; but it must re remembered that it does not intend to represent [he actual way in which the atoms are united in a molecule. It is intended to showhow the affinities, or degrees of chemical force, are probably balanced. Forinstance, in hydrogen sulphate there are four atoms of oxygen; but wc know they are not all combined with the sulphur with the same degree of force, and we know that

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A PRACTICAL TREATISE

HARMONIUM.*

By Hermann Smith.

THIRD DIVISION.—CHAPTER II.

Op The Upper Sound-board, Or Swell

"Fully to possess, to command, to rule su object wo mum first study 11 for its own sake. All beginning are easy, nnd it la the last «teps that are climbed most rarely and with greatest difficulty."— Goethe.

WE have brought the harmonium to tha particular stage of construction at which it may be considered as fully dcvelo]>ed according; to the intent of its original design. It has variety and power; it has its five and a half rows of reeds, each row possessing distinct qualities; it lias its second manual, by which musical effects valued by the artist may be obtained; is furnished with coupling movement; and is a complete instrument in all that pertains to musical execution. It is a rival to the pianoforte in the hands of the amateur, and is the "concert-grand'' ot its class. In making such an allusion wc assume that the harmonium we specify is equal in point of workmanship, and is a good specimen of the excellence which skill may achieve in the production of this species of instrument. If tho,woik of an amateur is taken to be the standard, then the harmonium should be placed in competition with a piano of amateur construction". If jcomparisons are fairly instituted between the .cardinal features or characteristics of the two instruments, we have little doubt of the general verdict being in favour of the harmonium on the gronnd^of its superiority as a generator of sounds of varied character and impressive fulness; setting aside the dexterity of the performers wc believe that it has in itself higher capabilities for satisfying the musical susceptibilities of onr organisation. Some will smile and say, "Of course you do; personal partiality influences such an expression of opinion." Doubtless, yet how can it be otherwise? Goethe in his mature wisdom, and knowing his own human nature, says, " I can promise to be upright, but not to be impartial." A noble, large-minded utterance; one which all may profitably lay to heart and remember. We cannot be. free from partiality in judgment and opinion. Like will tend lo its liking. By our observations we would intimate that we who give our attention to the harmonium, that amateurs who devote time and money to the practice or to the construction of the instrument, are driven by an impulse stronger than mere preference or casual fancy ; are impelled to do so that we may satisfy an irrepre.-sible longing for qualities of tone, for varieties of melodic charms, and sustained and richly-coloured harmony, which we feel the pianoforte is wholly inadequate to supply.

As the representative of its kind, the Harmonium ut the pcint wo have reached may be held to be complete, but beyond the ordinary requirements ol' the musician there is a s; eciality of demand, t;. meet which the instrument will have to extend its scope, to take new rank, anil invade by ronsent

• The copyright ot these letters is reserve) by tinAuthor. They were commenced in 1H, and coniium*1. iu No». 9i), us, 100, lor., K"J, no, 11*. vi*. isi'>, l&i, i;v.. lit'., Hi, 151, 16:!, 106,17:', ISO, 100, all ol which arc lot*.hid except No. PS.

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the province of the organ. Many changes of plan and purpose become expedient; to fulfil the duties of its higher state, expendimreon a grander scale is inevitable, we must set up additional soundboards, increase the numbers of the rows of reeds, provide ampler reservoirs, and lay down a full scale of German ped>ils—the pedals, the ambition of every musician, the organist's own inalienable estate, the broad dominion of his pride.

"How many rows of reeds can I have in an harmonium?" is the first question that presents itself to the enthusiast who happens to possess a roll of bank notes. It would not be courteous to reply, " As many rooms as you cum in a house that you contemplate building," but in truth the whole question is one of expense in relation to comparative utility. If the space to be occupied is limited to a small area, the increased number will 30 cut up and cramp the space that comfort and convenience will be sncrificcJ. In the attempt to do too much in limited compass or with restricted means, real worth will be swallowed up in display. Everything depends on judiciousness iu plan. Additional rows of reeds demand extra space, not alone for the sake of mechanical facilities of arrangements, but for ilicir exercise of power. Unless there is ample room for the expansion of tone, a lart'e instrument will be a very lame and impotent affair. Given, space, money and time, skill and experience, and it would be difficult to fix a limit to the musical effects possible to the harmonium. Let us restrain ourselves to an average want—namely, an instrument with sufficient volume of tone to afford to the organist a means of estimating at home the character of the music as he will give it upon the organ; that this volume of tone shall be capable of every gradation of light and shade, ranging from pianissimo to fortissimo, and shall be separable in distinct varieties of quality. With the swell manual and the ¡pedals, the harmonium is then qualified for rendering a faithful copy of the organ's music.

The additional souud-bound and reeds shall first receive attention. The illustration shows an upper sound-bound with three rows of reeds. These, we think, will fully meet the conditions stated, not too many to be cumbersome by the extra size of iustruineât they involve, and yet sufficient for the end in view. Four and half rows of reeds on the lower manual, three rows on the upper manual, and two rows on the pedals. Well planned and skilfully carried out, this instrument will possess a grandeur of tone fitting it to be the substitute for the organ, and affording the means of a daily familiarity with the works written for the king of instruments, the practice in which the

musician never ceases to covet opportunité f or
at his own hom e.

A large instru m nt like this w ll be tw
or eight inches in depth from front to back, and to
economise space we find it desirable to arrange
our plan for an upright Sjuiii board independent
of the other. To mako the a Idilio n as an exten-
sion of the horizontal sound-board we should
encroach on ground space to the extent of quite
another foot. Few rooms would afford to give up
so much space, and not only would the shape of
instrument be disproportionate, but the sound-
board would be too ponderous and clumsy fori
handling in tuning and adjusting. Free access
to every part we must have, and with as little
displacement as possible. So we place it upright
and fix it to a back-board, contriving that it shall
swing ou side-pins or screws, and yet when closed
shall press tightly against the back-board, with a
roll of wad intervening to make it air-tight, and
also in the same way press upon the trunks which
are carried up from the vilve-board to meet it.

You will notice that there is a side-iron project-
ing at the bottom of the sound-board, by which it
is screwed to the side of the case. It the height j
is sufficient to allow the lifting up of lower sound-
board, then this plan may be allowed, but other-
wise it will be better to slot or cut the eide-iron
up to the hole, so that the sound-bo ind shall be
capable of being lifted off the screw-pins when
requisite to have it out of the way for operations
on the lower portions of mechanism. It can be
taken away in a moment when the upper hooks
that fasten it are released. The manual itself
should be arranged that it may be diseHgaged,
taking with it that portion of the action work
which is made a fixture to its frame; this consists
of a stout bar and action-rail, with its series of
right-aiigled levers, called "squares," although
when shaped they look more like triangles or
cranks, each having a spring keeping it down on
the resting-rail, which, as you will see, prevents
its descent below a determinate level, therefore
preserving the keys to an invariable level, their
own weight of balance to fore-end keeping them
up to their proper contact with the squares;
cloth washers are required, placed between, to
prevent noise and abrasion of surfaces, and cloth
also along the rest-rail. The springs, sixty-one
in number, combined together, will exercise a
large amount of pressure, and need that the bar
and uction-r.iil should be firm enough to be free
from any chance of bending upward by the
strain. At the upper arm of each square or
crank a tapped wire passes through, having a
button on its point, which can thus be screwed up

to its work with utmost fineness of adjustmol
The remainder of the mounting of the sourr
iioard corresponds with the method adopted in'
horizontal plan. A . toning-leather covers ,'
stems, and beyond that a cover or encb
wood, sliding in grooves or fitted in any <
manner to the sides of the case, and геЛя
pleasure; this cover may also be fitted »ilk a
shutter upheld by a rod connected with i?top-
rod, when the stop-rod is drawn, the lower «sitf
the lifting-rod being thrown out of the veruai,
allows the shutter to open sufficiently to aftrt
greater freedom to the tone. Another arrange-
ment of shutter and a different method of carrying
nut several details will be given in our next. In
t'i • present plan the admission of wind is Ъу
trunks at either end of sound-board; by this we
save something in depth, a consideration of some
moment, though it be only a saving of an inch or
two, and therefore we present it first; it has its
disadvantages, but then we already have end
space to spare, the key-blocks of large instruments
being always made wide—from four to six inches,
and the amateur can allow this excess in length
often much more readily than he can an increase
in depth.

Fig. 2 gives a view in section of the sound-
board, showing the added length of sonnd-boanl
and disposition of the wind-way to each register;
the whole face of these is covered over when
finished. The trunks upward from the valve-
board will have to correspond with these. On
the top of the trunk each division is to be sepv-
I * rately wadded or leathered, to make an air-tight

connexion. Below these trunks the admissionvalves are fitted on the under side of sound-board, in the same manner as the valves belonging to lower sound-board, and actuated in a precisely similar way by stop-rods and levers, presenting no complexity for the consideration of the amateur, and therefore needing no further exp "nation. It cannot, however, too strongly be pressed upon hie attention, that with the enlargement of his aims the tax upon his skill, ingenuity, and patience will increase in compound proportion; feet six ' "Зе тп"ф1'с*(У of details, the relations of the various portions of the mechanism each to each, and each again to the whole, will demand from him great watchfulness, and an accuracy which the constructor of smaller instrnments is never called upon to display. Those who have never undertaken such work cannot imagine the amount of patience aud sagacity they will be called upon to exercise before they can bring their task to even an approximately satisfactory condition. It may no doubt appear to most amateurs that the building of a large instrument isonlv a multiplication of the work of small (ones—a question of time and expenditure which depends solely on his own good pleasure. Speaking from experience we know differently, and do not say so to discourage you in the attempt, but rather to incite you to energy and perseverance, under a full sense of the high task undertaken, and anxious also to give you the assurance that success, when achieved, amply repays for all the labour and patient care, and thoughtful endurance. Love your work for itself, not for the show you ein make of it.

Of the characteristics which it is desirable the registers of upper manual should possess, whether treated as the correlative of the swell organ or of the choir organ, we shall speak in another chapter.

(To be continued.)

HALLEY'S COMET. (Concluded from page 7S.) By Omicron. TT will have been noticed in giving the history -*- of the comet, that from the time of the discovery of its periodicity till its final disappearance, the name of no English astronomer is mentioned as taking part in the interesting calculations connected with it. In the last fact that we have to relate concerning the theory of the comet, however, one of our countrymen has distinguished himself in no moderate degree. The able Superintendent of the JVaulical Almanac at that, date applied himself to the task of computing an ephemeris of the comet, "the most extensive in its plan, and the most accurate in its execution, that the world has ever seen. Valuable as it

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able one, remarkable for the brilliancy of the
apparition, and the terror and consternation occa-
sioned throughout the whole of Christendom.
The tail of the comet on this occasion is recorded
to have been upwards of GO" in length, of a
►lightly curvilinear form like the blade of a sabre.
Historical readers will remember that at this
period Calixtas III. filled the papil chair, and
that Mahomet II. was at the zenith of hie
success, and Christian Europe threatened with
the inundation of the Moslem power. A brilliant
comet appearing at a critical moment snch as
then prevailed could nat be without its influence
in an age eminently superstitious. Accordingly
the comet was regarded with pleasure or dread,
as the spectator presumed it to betoken successor
failure. At Constantinople an eclipso of the
moon, at the time that the cornet was at its
brightest, drew particular interest to the pheno-
menon, and gave fnll work to the astrologers
of the period. A contemporaneous writer thus
describee this peculiarity in the heavens:—" Each
i.ight soon after sunset, a comet was seen like a
straight sabre, approaching the moon. The night
of ihe full moon having arrived, and then by
chance an eclipse having taken
place, according to the regular pro-
cess and circular orbits of the
celestial lights, ne is customary;
some persons seeing the darkness of
the eclipse, and regarding the comet
in the form of a long sword, which
arose from the west and travelled
towards the east, approaching the
moon, thought that the comet in
the form of a long sword, thus
designated with regard to the
darkness of the moon, that, the
Christian inhabitants of the West
had agreed to march against the
Turks, and would gain the victory;
bnt the Turks also considering
these things, became not a little
fearful, and had great discussions."
How the Christians argued so as
to augur defeat from the same
canse, history sayeth not, but Pope
Calixto« III. enjoined on all good
Christians a repetition of the Ave
Maria three times a day instead of
twice, and composed a prayer soli-
citing protection from the devil, the
Turk, and the comet. After some months daily
excommunication and cursing the comet waned
away, and finally disappeared, and the terror it
had spread was forgotten, though the deep-
rooted superstition remained as firm as ever.
It would be to lengthen this paper to a tedious
of it "wufbe l'1 unnecessary extent to follow the history of
the comet through the long interval of time that
the industry of Mr. Hind has pursued its motions
and identified its appearances. In 1378 the
comet does not appear to have created any
effect, and its return in 1301 was

to the physical astronomer of the present will be much more so to those that shall he observations of tbe year 1911." With ark from the lucid account the AstronoKoral has given ot the theory of the comet, je "Memoirs of the Astronomical Society," Л thêcarefnl study of which we recommend to every render, we quit this portion of the subject, and"aJJrefs ourselves to consider the history of the comet previously to the discovery of its

periodieity.

In order to discover whether the comet has been observed, or rather noticed, at the ti»es of its arrival at perihelion, previously to the discovery of its elliptic motion, it will not be sufficient to examine the meagre records of astronomy, as they have been preserved to us. Pingre has remarked in his valuable " Cometographie," that eomets were regarded not as objects to be observed, but as signs to be remarked, and to be compared with events; and that iu consequence the history and chronicles of every country and of every age were the most fruitful sources of information, and which it was the most essential to examine. Numerous difficulties beset the patient investigator of these ancient records. The very slight distinction that is drawn between cornels and meteors, the eccentric and ridiculons method of describing the appearance presented, the frequent errors that the observers have made in their rough observations of the comet among the constellations, are a few of the troubles that must be carefully put aside by him that shall attempt to unravel the mysteries that surround the writings of tbe middle ages. Another circumstance that tends to spread a degree of donbt over the motions of this comet is the varvingdeCTce of brightness that it has presented at "its different apparitions in modern times. In 1682, it appears to have presented a very brilliant appearance, while in 1607. and 1759, the brilliancy was less startling. In 1S35, again, it was certainly more conspicuous than in 1759, though less so than in 1682. It is verv possible, therefore, that at some of its returns it escaped notice altogether, and although tbe YabouT» of Mr. Hind appear to trace the comet np to the year 11 B.c., and recognise it at every apparition, great doubt attaches itself to some the intervening returns to the neighbourhood tbe sun. We shall therefore only notice those observations which appear to refer to the comet with tolerable certainty.

In 1607, which is the first date of its becoming visible before the time of Halley and Newton, sufficiently accurate observations were made to enable Halley to compute the orbit of the comet on the Newtonian hypothesis, and it will be | remembered that this apparition taken in conjunction with the one immediately preceding and following, led Halley to make his remarkable prediction. The light of the comet appears to have been " pale and waterv," and its course was I surprising through the consiellatioosof Ursa Major, Bootes, po^ibly unnoticed The Chinese and EnroSerpeus, and Opniuehw. As an instance of the Pea" observations, however, leave no donbt as to superstition that was prevalent at this period, we ; ltä «Ppearance in 1145, when it was visible may remark that the old chronicles mention I nearly two months, from the loth April to the among' the direful effects that the comet produced ■ ""■ "u" "The death of the Duke of Lorraine, and a great war between the Swedes and the Danes." The most careful observer of the comet in 1531

can scarcely claim a place in the ENGLisir Mechanic. The comet at this apparition wi,s regarded as presaging the conquest of England, by William of Normandy, and one far-seeing monk, probably aware of the expected attack, apostrophised the comet thus:—" There thou art, the source of the tears of many mothere. Long since have I seen thee; hut I see thee now moie terrible: thou thrcatcnest my country with complete ruin."*

As we attempt to trace the comet in the scanty information that ancient chronicles leave us, more and more doubtful do our conclusions become. In t)8!i and 913, Mr. Hind believes to detect the mention of the comet, but in 837 there is great doubt whet her the comet wae seen. However in 760, M. Laugier has shown with great probability that a very brilliant comet that appeared in that year was identical with that ef Halley ; and Mr. Hind remarks that the probability in his opinion amounts to little less than certainty.

From the same source that we derived the picture of the comet as it appeared in 106f, we present a sketch of a lomet that was visible in

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was undoubtedly; Appian, of Ingoldstadt, and
from his observations Halley has calculated the
elements of the orbit. Appian began to observe
tbe comet on the 13th of August, and appears to
have continued his observation till the 23rd.
Appian noticed that the tail was always turned
from the sun, and that when the comet's nucleus
*ank below the horizon, the tail disappeared with
a eeli-rity as if some cloud had suddeuly obscured
it. Appi&n't observations commence in the con-
stellation Cancer, and are pursued into Leo.
The comet is »id to have been of a bright golden
colour. A contemporaneous writer remarks that
on the 25th July, "nne poutre de feu" was
observed, and two comets appeared. The remark
evidently refers to a meteor, ami wc have intro-
duced it to convey some idea of the obscurity in
which the accounts are involved, and tbe necessity
of " sifting" the evidence before admitting it as
an astronomical fact. It is, however, right to
f-ay that Piogre remarks of this author, that it
would have been better if he had never written,
that be is inexact even in tbe dates of events that
liappcued in his own time, and that he manifests
no extraordinary credulity in everything tending
u the marvellous.
The next previous return, in 1456, is a remark-

The tail is said to have been 10 long, extending in a north westerly direciion.

In the Bayeux Tapestry is to be found the representation of a comet, which there is every reason to believe is Ilalley's, though Mr. Hind has found it necessary to advance the longitude of the perihelion 30«, to make the observations accord with the places deduced from the eelemnts of Halley's comet. We are able to give our readers a sketch of the comet as there exhibited, from Admiral Smyth's "Speculum Ilartwclli» anum."

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684, which was the year that Halley's comet would have been visible, judging by its period . f 76 years. The sketch is taken from the old Neuremberg Chronicle..' though, says Admiral Smyth, " from what authority the s'aid xylographors of that recondite work took it, does not appear."

The identity of Halley's comet with comets of the years 161 and 218, appears very probable. The observations are provided chiefly by Chinese historians of those dates, and the deduced elements exhibit some considerable marks of agreement with the general orbit of Ilalley's comet. The year 11 B.C. is the most distant date to which Mr. Hind has tarried his investigation, and the comet of that year is one of the most certain of the ancient appearances. All the circumstances of the observations arc in accordance with the motion of Halley's comet, if the inclination be reduced some 84 or У°, an amount which the perturbations of so long a period would be quite capable of effecting.

THE ENGLISH MECHANIC
LIFEBOAT.

OUR Lifeboat Fund, during the last week or
two, has increased but slowly. We think,
therefore, we are justified in making another
appeal to our readers, especially to thoee—the
vast majority — who have not yet favoured us with
their subscriptions. We have been very much
plcaeed this week with a donation forwarded to
us by Mr. Huret of £3 6s., which is acknowledged
elsewhere, and is sent by that gentleman as the
proceeds of a concert given at Heybridge, near
Maldon, Essex, in aid of the English Mechanic
Lifeboat Fund. The concert was given at the
head-quarters of the 1st Essex Engineers, and was
got up by Messrs. Mulley, Andrews, and Hurst,
in the employ of E. H. Bentall, Esq., M.P., of
the Heybridge Iron Works. Mr. Hurst has en-
closed us a very neat programme of the proceed-
ings, the song of the evening being, of course,
"Man the Lifeboat," sung by himself. Иг. Hurst

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expresses a wish, which we heartily endorse, that many other subscribers may adopt his plan, and that we receive many more subscriptions embodying the results of similar efforts for the cause of " our lifeboat." Another concert in aid of the fund will be given on the 21st inst. at Staunton Harold, Ashby-de-la-Zouche, under the patronage of the Earl and Countess Ferrers and the Lady Augusta Shirley. This concert has been originated by Mr. George Luff.

May we be permitted, for once, moro directly to appeal to those of our readers who can afford to give more largely? One of those seasons is now with us when it is especially "more blessed to give than to receive ¡" and to those who have no other special call on their generosity the English Mfchan'io Lifeboat affords a fitting object for many an Easter-offering. We do not at all wish to have to beg on behalf of our project ; we think better of our subscribers, and believe that next week's list will justify our good opinion. Tlie thousands of our correspondents who so generously afford aid to their fellow-readers which no money could purchase will not. we feel sure, grudge a few pence, pounds, or shillings', according to their means, towards the cause we plead.

PROFES80R HUXLEY Olí THE GEOLOGICAL PEDIGREE OF THE HOÄ3E.

О У Friday, April 8th, Professor Huxley delivered a 1 ce turc at the Royal Institution, before a very large audience, upon " The Pedigree of the Horse." Si» Henry Holland, В irt., F.a.s., presided.

Professor Huxley began, by sayuig that time now travels fasterthan it used to do. It was now in years since he had the honour of addressing a, juihlic audience on the origin of species and the theory of evolution due to the genius of Charles Darwin. At that timo the theory wa» passing through the trisd, through the struggle for existence, which all youthful organisms in nature have to undergo. On that occasion he succeeded so far in overcoming his natural love for peace und quietness—(laughter)—as to advocate what vas then a repressed doctrine. Now all wag changed. The doctrine which then was regularly refuted and overthrown once in every six weeks had since grown to such an extent that it was now the leading doctrine of most of the first scientific men in Europe, and he thought it would be well to yet up a little constitutional opposition to its tenets, for now it entered even into the consideration of its adversaries. The nineteenth century, as far as science was concerned, would be known in history as having given birth to two doctrines —namely, the doctrine of the conservation of force, and the doctrine of evolntion as set forth by Charles Darwin. The foundations of the first of these theories are as firmly set as the walls of the Royal Institution, but the other is not yet on o,uite such a stable footing. The doctrine reste upon three pillars of observation and experiment. The first of these is the production of living mattor from matter not living; the next is the production of new species by natural selection ; the third pillar was historical evidence of living aniimils succeeding each other in a way which met ♦he requirements of the dootrine. When these ehree lines of evidence were complete, what was now hypothesis would become theory. As regards the first of these we were now in an unsatisfactory state; as regards the second, in spite of an enormous accumulation of probabilities, we yet stand without the direct production of a new species from one common stock; but as regards the third point, which not long since was the weakest of all, it is now, in a sense, the head stone of the corner, and may be more satisfactorily relied upon than cither of the other two. The rocks reveal to us transitional forms between animals now existing and those long gone, and yield to the philosopher fossils transitional between groups of animals now far apart. At a lecture delivered at the Institution two or three years a_'0, he had brought under their notice forms transitional between the widely spread groups of birds and reptiles ; and the reasoning he then adduced had been rendered stronger by subsequent observation, more especially by the discoveries of Professor Cooke, of Philadelphia. What was required to form good historical geological «vidonce? Let A, 1$. and С be three geological strata, each successive one older than the other; and let X, Y, and '/. he groups of animal forms, succeeding each other. If he could show that there was a gradual progression of AX to В Y, and from В Y to С Z, it was the highest kind of

proof which could be given. But it is exceedingly hard to find evidence of this kind good enough to satisfy critical minds, and at prescut it would be very injurious to bring forward evidence of a less conclusive nature. But he had one particular case to bring before them, which he thought would stand any amount of worrying, and tearing, and pnlling about. The «ase in question was of particular interest, because it concerned an nnimal of which Englishmen were exceedingly proud, that is to say, the horse. He was told that some among his listeners were en the look-out for what are called "tips" in his lecture—(laughter)—but on this occasion he was going to treat the subject in a thoroughly scientific way, and none other. All animals and things which were very accurately and delicately balanced were apt to be very beautiful. On the same principle the beauty of the body of the horse probably has much to do with its being one of «he best possible pieces of apparatus for running swiftly along the land. Iii many respects tho organisatioH of the hors* departed in an extraordinary way from what miy be called "the average quadruped," and the peculiarities to which he desired to call special attention were those of the fon limbs, the hind limbs, and the teeth. What wa»aaUfd the "knee" of the horse was in reality the wrist of tho animal. Human beings had two-bones in the fore-arm, and this was also the case witij most quadrupeds, but in the horse these two bones were completely fused and bound together into one. In most horses and asses the two bones were soldered together, and the shaft of the ulna nearly disappeared. The horse's hoof answered to the fingers of the human hand, only iu the hoof some of the bones and fingers of the hand were missing, and the horse in reality rests upon the end of the nail of the middle finger. What has become of the other fingers? Two of. them were taken away, and two of the other bones were reduced to little splints, which could be seen from the outside of the horse's foot. This peculiarity was found only in these animals. Iu tho hind-legs of the horse the small bone was reduced, ал in the fore-legs, and the middle toe was there with its nail made into a hoof. The horse had also a peculiar construction of the grinding teeth of the upper and lower jaw, some portions of these teeth being harder than other portions, so that each tooth wore u nequally iu different parts, whereby it always had a rough surface for grinding purposes, something like the face of a millstone. Tho tooth was composed of ridges and pillars, bone and cement, very curiously arranged with respect to each other, and a set of such tooth made a very officient mill for the use of the horse. In a very young horse—that is to say, in ahorse a toot long, before it was born—thero were tho remains of the ulna much more complete than in the grown animal, and in the young horse the rudiments of the toes were larger in proportion than in the adult. Sometimes horses were born with extra toes, and thero was a specimen of this kind in tho Museum of tho College of Surgeons. At the present time also there was a South American pony in tho Victoria Docks with a» extra toe to each hoof, and the toes could be folt by the finger. If these facts were interpreted by the doctrine of evolution, what did it say? It said that the missing toes of the horse must have vanished from some animal preceding the horse, which had the normal number of toes, ami that the ancestors of the horse must at one time have had the leg aud foot bones compite, although these were blotted out before the horse was turned into a perfect running machine. It als» said that at one time the toet'h of the horse must have resembled those of other herbivorous animals. It also said that the young or embryonic form often resembled the common form more than the adult animal did. The extra toe, in some cases, wa» probably bat a réversion to the type of some remote ancestor—nevertheless, he did not lay much stress upon this point himself. Now what tibí pakeontology say to all this? The remain« ее the horse were found in npoiu*ion>aB over Europe-end A«ia, and they existed, in geological strata of enormous antiquity; they coulii be traced back to periods long before any indications of the exie;encc of тел had as yet been found, yet the horses and asses of that remote period resembled in nearly every respect til* horses and asses which now ran wild in many pans of Asia and Africu. On going still further back to the upper mioccne period—a time when the world altogether differed from its present condition as regarded its geographical features—the horse was still found with all its present peculiarities, and the two differ from each

other only in minute details. But side by sido with the remains of the horse in this deposit were the remains of another horse-like creature called the " hipparion" or " little horse." As much wns known about the hipparion os about the horse. There was no break ia the series of time, for both are found in the same deposit. In the fore limb of the hipparion the leg bones were united, but tho extra one was traceable, and the leg bones were nearer to the average type; the animal also h two little hoofs or fingers, one on eaeh side of the main hoof, bnt they appeared to have been of Do use whatever. The tooth ¡was still very horsey, but it was changed nearer"to the ordinary type. There was, therefore, in the upper miocène an animal which resembles the horse in some particulars, and departs from it in others. Professor Huxley continued: Did the horse succeed the hipparion? Was it conceivable that the one animal was struck out of existence altogether, and that the other was then created afresh out of nothing? Was it thinkable? If so, he might as well give np his theory altogether. Having proceeded thus far, the investigator turns with considerable confidence to bis geological remains to look for the hypothetical ancestor of the hipparion. This ancestor was found in the anchitherium, and its remains were found in the lower miocène, but not in the upper as yet, so that there is a greater gap between the anchitherium and the hipparion than between the latter and the horse. In the anchitherium the log bones are still more separated; it has three toes in the fore limb, the two outside ones beiug half as big as the middle toe, so that the foot somewhat resembles that of the tapir. This animal, therefore, has the fore foot which theory [requires that it should have. In the hind leg the bones are more divided than in the case of the hipparion, tho hinder feet have three toes, and the teeth have not the plasticity of those of the horse, but approach more nearly to those of the ordinary type. Thus in these three animals there are proofs of gradual progression in teeth, hind legs, and fore legs, all the rest of the organisation of each being horse-like. He submitted, then, that these animals fulfilled the conditions which he laid down at the beginning of his lecture, and that it was impossible to obtain evidence *more complete in kind than this of the pedigree and origin of the horse. If a man says that be can trace his pedir groe back to the time of the Conquest—well, there is no harm in that; but if he »ays that he is descended from King Arthur or Noah, the evidence is not worth much. In like manner the history of the horse had been traced by him in the lecture as far back as the Conquest; but he wished to go a little further, and look a little over the edge of certainty, to get some idea of what is lying on the other side. Ho then pointed out that iu the eocene period there are remains of animals which are probably remote ancestors of the horse; the plagiolophus minor to wit. This animal more approaches the rodents in type, but it differs from the horse only in degree, and not in kind. He concluded by remarking that if Darwin's doctrine is made out in this one case of the horse, i: is strong evidence that similar modifications hare taken place in all cases.

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PROFESSOR TYNDALL ON FILTERED AIR.

PROFESSOR TYNDALL has supplemented his famous lecture on " Dust and Disease." In a letter to the Times he describee and defines the germ theory of the putrefaction of wounds: —The entrance of air into a wound (he says) is the dread of the surgeon. When an abscess is opened he must prevent the air from mingling with the blood-clots if he would avoid putrefaction and its teeming accompaniment of animalcule life. Some eminent London surgeons inform me that they never squeeze an abscess, lest when the pressure is relaxed the air should be sucked in. Now, whence this dreaded power? Is it the air itself thut causee putrefaction, or is it something carried mechanically by the air? A follower of Gay-Lussac would affirm the former : » heterogenist would refer the animalcules to spontaneous generation ; a holder of the germ theory would ascribe tho putrefaction to seeds or eggs floating in the atmosphere, and which, when »own upon the wound, sprout into this crop of minute organisms. Do any data exist which will enable us to say with certainty which party is right? think so. It would be very difficult to redue* the purifying power of pure air, even if it exist. »

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