Pl. V. fig. 2). It is seen from the right side. At ov is the orifice of the generative and aquiferous systems, and at r that which leads into the pleural sac ("poche périphérique "), p. At the posterior part of this sac is seen the slit y, by which it communicates with the glandular sac ("poche centrale"), g 8. Anteriorly, at z, is the opening by which the latter sac in its turn communicates with the pericardium, p, which invests the ventricle of the heart, h, and that portion of the intestine which passes through it. At p a the posterior adductor is represented in section, and in front of it are seen the culs de sac, which are formed by the reflection of the " organ of Bojanus" over it dorsally and ventrally.

Fig. 5 is a kind of ground plan of the "organ of Bojanus." At the anterior part is seen the wide communication, wanting in Unio margaritifer, between the pleural sac of either side, p s, ps, and its fellow. Between the sacs lies the venous sinus, v 8. The rest of the letters have the same signification as they have in fig. 4.

FIG. 6 is a modification of a figure (13) in Professor Huxley's Elements of Comparative Anatomy. It is a diagrammatic representation of a vertical transverse section through an Anodon: м M, Mantlelobes; o g, ig, outer and inner gills respectively; v, ventricle; and a v, auricle of the heart; i, intestine in section. The remaining letters have the same meaning as they have in previous figures.

FIG. 7 is a plan of the nerve system of the river-mussel. At lg is seen the left labial ganglion, which is joined to its fellow by a nerve cord. From each labial ganglion are seen to pass, in addition, the following nerves:-A branch running straight forwards to the anterior adductor, and another backwards to join the bilobed branchial, or "parieto-splanchnic " ganglion, b g; a cord passing down vertically to the pedal ganglion p g, while another runs outward to ramify over the anterior portion of the mantlelobe.

From the pedal ganglion are given off branches-only a few of which are represented in the figure-to the auditory organs and foot; from the parieto-splanchnic ganglion passes backward on either side a nerve to the rudimentary siphon, while outwards run branches to the gills and posterior part of the mantle lobe.

The line of dots indicates a communication, wanting in Anodonta, but present in the marine mussel (Mytilus), between the anterior and posterior pallial nerves.

Owing to want of space, only part of the pallial nerves on the right side has been figured. Their course is, however, similar to that seen on the left side.

ON A SIMPLE DECIMAL SYSTEM FOR ENGLAND.

BY ROYSTON-PIGOTT, M.A., M.D., Cantab., M.R.C.P., F.C.P.S., F.R.A.S., late Fellow of St. Pet. Coll. Cambridge.

IN

attempting to revolutionise our national standards, we must not forget that history is apt to repeat itself. The consequences, therefore, of the arbitrary introduction of the French metrical system are not unworthy of attention.

In 1795 a provisional measure of the ten-millionth part of the earth's quadrant, reaching from the equator to the pole, and embracing 90 degrees of latitude, was adopted as the French unit of length.

In 1799 two parallels of latitude between Dunkirk and Barcelona having been carefully selected for measurement, the unit was fixed at

Or rather

And the litre at

And the gramme at

39.37079,

39-37078980 English feet;
1.760773 English pints;
15-43234874 English grains troy.

Seventeen years later the new Government standards still met with such violent opposition on the part of the great mass of the French people that, on March 12, 1812, the Government authorities, embarrassed with the intensity of the popular discontent, tardily conceded the use of the ancient "Système Usuel."

By this concession the people regained the use of

The double boisseau, boisseau, the half, quarter, third, sixth, eighth, and twelfth of a boisseau. The pound, or livre, of 16 onces, each once containing 8 gros, and each gros 72 grains.

How could it be possible for the illiterate classes to master

the jargon of the metric system, compounded of Latin and Greek phraseology, in a single generation? In 1840, however, the system was again enforced by a strong Government. Nearly fifty years, or nearly two generations, had passed away before the nation could be made to learn the unwelcome task imposed upon it.

The common people have a most natural and intuitive habit of reckoning by halves, quarters, thirds, eighths, &c. &c., and they go on subdividing, and then adding, particularly parts, with a surprising acuteness and accuracy. The decimal system rendered mental arithmetic at first impossible.

Our own yard admits of no less than six modes of division, without breaking the component inch.

Even to this day the French line and inch are still in use. Nobert's celebrated test lines are ruled in bands of the Paris line in breadth. And many scientific instruments are still constructed by this obsolete measure. It is the twelfth part of the Paris inch, and too convenient to be entirely discarded.

The experience of the greater part of a century is in favour of units of measure and weight, easily divided into integral parts, rather than decimals. No whole number can be divided by three, six, or seven, unless it is a multiple of one of them, without an array of decimal figures accurately interminable, and to the poor man incomprehensible. It may safely be asserted that a plébiscite of Englishmen would give the vote in favour of retention and adaptation of our own time-honoured standards, rather than for abolition. This is an affair which pointedly

"Comes home to every man's business and bosom."

There is another consideration which has some weight, as against abolition of the standards. Almost every kind of special calculation, in particular departments of commerce or science, is wonderfully abbreviated by the principle of common factors. Owing to the frequency with which either 2, 3, or 5, or multiples of them, form bases of calculation, proportions or ratios innumerable have been gradually worked out, saving an enormous amount of labour.

If the reader be asked how many feet per second is traversed by a racehorse going at the rate of 30 miles per hour, an array of figures will be employed to ascertain the result. But if he be informed that 22 feet per second is exactly 15 miles per hour, he will at once perceive that 30 miles per hour is 44 feet per second. A few similar instances may be adduced.

A square mile of country receives 27 inches deep of rain per annum: this is very nearly 2 cubic feet per second.

Interest. Since 73 is a factor in 365 days, five per cent. interest on 1,000l. is exactly 10l. in 73 days: 1. for 100%.

Levelling.-Square of miles distance bears the same proportion to the inches difference of level (owing to earth's curvature) that 58 bears to 9.*

In surveying, 22 yards wide for a railway or road absorbs 8 acres per mile.

It is unnecessary to quote further instances to illustrate the use of common factors in units of measure.

Englishmen are attached to their British inch, pound, and gallon; and the evidence for abolishing them has yet to be produced. In the French markets, one still hears the prices asked in sous, francs, and demi-francs, and occasionally in centimes, and certainly no subdivision of these less than fives. In the same way, one may predict that our people will cling to the pound, shilling, and pence, the foot, yard, and acre, and the pint, gallon, and pipe, long after mètres and litres may have gained a footing here.

The arguments used by ultra-decimalists occasionally, rather weaken their cause. At the conference of the International Decimal Association, one of the principal speakers declared, that "the poor man who went to market for one pound and three-quarters of mutton, at sevenpence three-farthings a pound, would be sure to be cheated by the butcher." Let us present to this unfortunate victim of rapacity a picture of the new safeguard for his protection (which of course could be easily explained to the poor man)

The correct price which John should pay would therefore be 13 pence 2 farthings and one-quarter. John, however, would probably think (upon consulting the talisman of his forelock) that his own way (presumptuous man) was "far away" the best. He would reckon thus: two pounds would cost 15 d., a quarter

A very heavy deposit at a bank was made recently of 500l. against proving the curvature of water; and this sum was actually forfeited as an absurd example of ignorance of the effect of gravity. Had the following beautiful ratio (depending upon common factors) been known, "the square of the minute's dip of horizon at sea is of the feet altitude of the observer," the bettor would have been 5001. better off.

9

of a lb. twopence nearly, and, taking this from 15 d., he would pay 13 d., and probably the butcher would have the worst of the quarter-farthing bargain. This triumphant exposition of the advantage of the decimal system for marketing would doubtless gain many adherents to the good cause.

America is satisfied with a coinage which is seldom used or seen the half cent, the 100th part of the dollar of four and twopence; and the English, except for very accurate accounts, are content with the farthing as the lowest coin, as the tenth part of a penny is totally unnecessary for common use.

The value of units of measure which contain factors of some one or more of the integers 2, 3, 5, 7, may be considered of sufficient importance for retaining as far as possible our national standards. Transition and accommodation, rehabilitation and revision, appear far more desirable than abolition and destruction. With this view, the problem of forming a decimal system (the advantages of which in certain cases are generally acknowledged) is entangled with difficulties of no ordinary kind; so much so, that no surprise should be felt at the lapse of fifteen years already during the consideration of this great question. This question lies, intrinsically, between destruction and adaptation. To the latter the writer gives his adhesion alone. Adopt, with the ultra-decimalists, the metric system full and complete, and a dead-lock would be given for a time to every counter in the country, to every shop and every barn. A gradual transition can alone avoid a concussion between scientific scales and the old standards. On the other hand, if new scales can be arranged, admitting easy transformation and an optional and gradual transition, practical superiority would quickly establish the new system.

Commencing with the gold standard, at present, the sovereign (containing 22 carats pure gold *) is at sixes and sevens with all foreign coin. Two courses are open, either to depress its value to 25 francs, or raise the value of the franc, so as to make 25 francs equal to it in value. Whichever course is ultimately adopted, the conversion of English money into French will no longer require arithmetic beyond multiplication or division by 4. But even supposing the sovereign remains worth 25 francs 20 centimes, the following method is so extremely simple as to be worthy of insertion here as a national question.

Regard 25-20, without the decimal point, as 2520; subtract from it a third of a seventh

7)2520

3)360
120

22 out of 24; 18 carats standard means 18 pure out of 24 parts.