Fish Life.-This Devonian system is celebrated for the great development of fish life, which the fossils of the epoch announce. This subject owes much of its completeness to Agassiz, who published, in 1844, a monograph upon the Devonian fish. He ranked the sixty-five British species under his two classes, the Placoid and Ganoid, which we have described in a previous lesson. Of the placoids no entire skeletons are preserved, but their existence is indicated by the frequent occurrence of finspines-ichthyodorulites-and teeth.

The ganoids comprise the greatest number of these palæozoic fish. Those early seas must have presented a sight indeed

the restitution of some of these animals is very imaginative, and may be wrong. The shields of the pterichthys and the coccosteus may not represent the full extent of their bodies as they do in the figure.

The fauna of the period is given by the remains of fuci or sea-weeds, some marsh plants of the bulrush species, and sedge (juncites); and of land plants, some bear a resemblance to the lepidodendron and calamites of the carboniferous period.

The yellow sandstones of Ireland afford some very fine fossila of the Adiantites Hibernicus (Fig. 64). The venation of the leaves is wonderfully preserved.

strange to us. No reptiles were to be seen, perhaps no birds, but the power of life seemed to have given itself full liberty within their waters, and there swarmed fish of every description, wonderful creations, some entirely encased in enamelled plates, which shone and reflected the glistening sunlight as they shot with marvellous velocity through the water. These strong plates must have been for some material use, and what other purpose could they serve than for defence? How powerful the enemy to resist whom such casements were required! What desperate encounters-what a violent existence do these facts suggest ! Besides the Pterichthys Milleri, which has been illustrated in Fig. 21 (Vol. IV., page 61), the following specimens of the fish of the period are figured in the cut accompanying this paper-Cephalaspis Lyelli (Fig. 64); Coccosteus cuspidatus (Fig. 65); Polypterus (Fig. 66); Diplocanthus (Fig. 67).

Still, with regard to these figures, it is only fair to add that the reader must remember that, although we know more about the fish of the Devonian age, as a class, than we do of any other class whose records the rocks preserve for us, yet

TABLE OF FOSSILS OF THE PERIOD.

Plants.-Calamites, Lepidodendron, Stigmaria, Fuci.
Corals.-Amplexus, Chonophyllum, Endophyllum, Favosites, Polymorpha,
Cyathophyllum, Heliolites porosa, Aulopora, Spongiophyllum,

Hallia.

Polyzoa. -Fenestella, Retepora, Hemitrypa, Ptylopora. Brachiopoda.-Athyris, Atrypa, Calceola, Strophomena, Orthis, Pentamerus, Producta, Rhynconella, Spirifer, Stringocephalus, Terebrabulæ, Virgo, Uncites, Davidsonia. Conchifera.-Avicula, Aviculopecten rugosus, Corbula, Cypricardia, Megalodon, Nucula, Cucullea. Gasteropoda.-Euomphalus, Loxonema Murchisonia, Natica meridionalis, Pleurotomaria turbo, Vermetus. Pteropoda.-Bellerophon, Porcellia. Cephalopoda.-Cyrtoceras, Goniatites, Nautilus germanus, Orthoceras, Crustacea.-Phillipsia, Trimerocephalus harpes, Phacops, Pterygotus. Echinodermata.-Cyathocrinus, Hexacrinus, Adelocrinus. Fish.-Acanthodes, Actinolepis, Cephalaspis, Cheiracanthus, Cheirolepis, Coccosteus, Dendrodus, Diplocanthus, Dipterus, Holoptychius, Osteolepis, Polypterus, Platygnathus, Pterichthys, Ptychacanthus.

Clymenia.

δίπλα τιμήσομαι, φωράσαμαι.

Future Tense. φιλησομαι,

μισθωσομαι.

Κ. ετιμησάμην,

Sing. τιμία-ου)ῶ, τιμ(α-ε)α-σθω,

Dual, τιμ(α-ε)α-σθον,

τιμία-ε)α-σθων,

Plur. τιμ(α-ε)α-σθε,

φιλ(ε-οι)οῖ-ντο,

IMPERATIVE MOOD.

Present Tense.

φιλ(ε-ου)οῦ,

φιλ(ε-ε)ει-σθω,

φιλ(ε-ε)εῖ-σθον,

φιλ(ε-ε)ει-σθων,

μισθο-ω) ω-μαι. μισθ(ο-η)οῖ. μισθο-η)ῶται. μισθίο-ω)ω-μεθον. μισθο-η)ῶ-σθον. μισθ(ο-η)ώ-σθον. μισθίο-ω)ω-μεθα. μισθο-η)ῶ-σθε. μισθο-ω)ω-νται.

μισθ(ο-οι)οι-μην. μισθο-οι)οῖ-ο. μισθ(ο-οι)οί το. μισθο-οι)οι-μεθον. μισθο-οι)οι-σθον. μισθο-οι)οι-σθην. μισθ(ο-οι)οι-μεθα. μισθο-οι)οῖ-σθε. μισθο-οι)οί-ντο.

μισθο-ου)οῦ. μισθο-ε)ου-σθω. μισθο-ε)οῦ-σθον. μισθίο-ε)ου-σθων. φιλ(ε-ε)εῖ-σθε, μισθο-ε)οῦ-σθε.

τιμα-ε)α-σθωσαν φιλ(ε-ε)ει-σθωσαν μισθο-ε)ου-σθωσαν οτ τιμ(α-ε)α-σθων, οι φιλε-ε)ει-σθων, οι μισθο-ε)ου-σθων.

VERBAL ADJECTIVES.

Τιμη-τεος, -τεα, τεον; φωράτεος, -τεα, τεον; φιλη-τέος, στεα, -τεον ; μισθω-τεος, -τεα, τεον.

REMARKS ON THE CONTRACTED VERBS.

The verbs in ew with monosyllabic stems, as πλεω, I sail; πνεω, I breathe; θεω, I run, etc., admit only the contraction in e (made up of eet or ee), and in all the other forms remain uncontracted, as→→→

Active.

Pres. Ind. Πλεω, πλεῖς, πλεῖ, πλεομεν, πλεῖτε, πλεουσι.
Subj. Πλεω, πλεῃς, πλεῃ, πλεωμεν, πλέητε, πλέωσι.
Imper. Πλει. Inf. πλεῖν. Part. πλεων, πλεουσα, πλεον.
Impf. Ind. Επλεον, επλεις, επλει, επλεομεν, επλείτε, επλεον.
Opt. Πλεοιμι, πλεοις, πλεοι, etc.

Middle.

Pres. Ind. Πλεομαι, πλεῃ, πλεῖται, πλεομεθον, πλεισθον, etc. Inf. Πλεῖσθαι. Part. πλεομενος. Impf. επλεομην. The verb dew, I bind, admits contraction in all its forms, especially in its compounds, as το δοῦν, του δοῦντος, διαδοῦμαι, κατεδοῦν; but not δει, it is necessary, nor δεομαι, I must.

Several verbs depart in contraction from the ordinary rules: αε, αει, an, an become η and y instead of a and q; as, ζαω, ζω, I live, ζῇς, -η, -ἦτον, -ῆτε ; inf. ζῇν; imperat. ζῆ; imperf. εζων, -ης, -η, -ῆτον, -ητην, -ῆτε. Also πεινα-ω, πεινώ, I am hungry, inf. πεινῇν, etc. ; διψα-ω, διψώ, I am thirsty, inf. διψῇν. Further, κναω, κνῶ, I scratch, inf. κνῇν; σμαω, σμῶ, I wash, inf. σμῇν ; ψαω, ψῶ, I rub, inf. ψῇν; χραομαι, χρῶμαι, I use, need, χρῇ, χρῆται, inf. χρῆσθαι. 30 αποχρῶμαι, I waste, inf. αποχρῆσθαι ; αποχρη (abbreviated from αποχρῇ), it is sufficient, inf. αποχρῇν, impf. απέχρη; χραω, χρῶ, I give an oracle, χρῇς, χρῇ, inf. χρήν.

Respecting the use of the Attic forms of the optative in ην, observe that in the singular of the verbs in ew and ow the form ony is preferable to the ordinary form, and in the verbs in aw is almost exclusively to be employed; but in the dual and the plural the ordinary form in all three kinds of verbs is more usual. The third person plural has regularly the shorter form. State what is the part, and what the English, of the words in the following exercise :

Ετιμησω. εμισθωθην. φιλητέος, τετιμηκα, τιμητέος. τιμωμι. φιλοιεν. τιμῳμην. τιμῳμεθα. τιμῳ. τιμῷεν. μισθοιτε. ετιμα. εφίλει. εμισθου. εφίλειτο. μισθοῦτο. ετιμωμεν. εφιλείτε. εμισθουτε. ετιμασθε. εμισθουσθε. τιμων. τιμωσα. φιλούντος. τιμωμένη. φιλουμενου. μισθοῦσθαι, μισθοι, φιλῶμαι, φιλούμαι. φιλῃ. φιλεισθαι.

Give the contracted form for these uncontracted forms :Τιμαεις. φιλεω. τιμαετε. τιμας. φιλεομεν. τιμαουσι. εμισθος. ετιμαεσθον. εφιλεόμην. εμισθοετο. μισθούμενος. τιμαοιεν. φιλεοι· μεν. μισθοοι. μισθοοιμι. τιμάοιτο. μισθοοιντο. τιμαοιημεν. φιλεοιην. μισθοοιητον. μισθοοιητε. φιλεοιντο.

Write out in full, according to the paradigms, the following verbs, first in an uncontracted form, and then in a contracted form, and then again in the two forms combined :-

Φοβεω, I frighten, φοβήσω, πεφοβηκα, πεφοβημαι.
Χωρεω, I yield, χωρησω, κεχωρηκα, κεχωρημαι,
Ποιεω, I make, ποιησω, πεποιηκα, πεποιημαι.
Αγαπαω, I love, αγαπησω, ηγαπηκα, ηγαπημαι.
Νικαω, I conquer, νικήσω, νενικηκα, νενικημαι.
Δηλόω, I show, δηλωσω, δεδηλωκα, δεδηλωμαι.
Χρυσοω, I gild, χρυσώσω, κεχρυσωκα, κεχρυσωμαι.

KEY TO EXERCISES IN LESSONS IN GREEK.-XXXII.

EXERCISE 94.-GREEK-ENGLISH.

1. I was setting upright. 2. I was playing drunken pranks. 3. I made a disturbance. 4. I have set upright. 5. I was serving. 6. I was living. 7. I was supporting. 8. I was narrating. 9. I have built. 10. I was throwing. 11. I was leading. 12. I have hoped. 13. I have entreated. 14. I have associated. 15. I have lamented. 16. I was praying. 17. I spent. 18. I was following. 19. I had founded. 20. I had taken. 21. I have been dug. 22. I was casting away. 23. I was preparing. 24. I was in a state of displeasure. 25. I have been a benefactor. 26. I have narrated.

KEY TO EXERCISES IN LESSONS IN GREEK.-XXXIII. EXERCISE 95.-GREEK-ENGLISH.

1. The soldiers were ordered to go against the enemy. 2. Sparta was once fearfully shaken by an earthquake. 3. The power of the Persians has been broken by the Greeks. 4. The enemy were shut up in the citadel, 5. The barbarians took to flight when they heard the Greeks dash their shields against their spears. 6. The war was stopped. 7. We hope that we shall accomplish all things well. 8. I would that I might accomplish all things well. 9. The treaty has been broken by the barbarians.

EXERCISE 96.-ENGLISH-GREEK.

1. Οι στρατιωται προς τους πολεμίους πορευεσθαι κεκελευσμένοι εισιν. 2. Η πολις ημετερα υπο σεισμου τεθραυσται. 3. Εκείνη ή πολις ύπο σεισμού θραύσθήσεται. 4. Η πολις ύπο σεισμου σείεται. 5. Η των Περσων δυναμις ύπο των Έλληνων εθραύσθη. 6. Οἱ πολέμιοι εις την ακραν κατακεκλεισμένοι 7. Ai aonides upos тa dopaтa vño тWV яodeμιwv expovalneav. 8. 'O πόλεμος πέπαυται, 9. Ο πόλεμος πεπαύσεται, 10. Eide zavтa kadas av σαίμεθα. 11. Κελεύσαι ράδιον εστιν η ανυσαι. πολεμίων λυθήσεται.

εἰσιν.

12. Η συνθηκη υπο των

LESSONS IN MENSURATION.-I. MENSURATION is a comprehensive and general term, signifying the determination of the extent both of lines, surfaces, and solids, and is derived from the Latin word mensura, a measure; and it is our purpose to explain in the following chapters, as simply as possible, the rules by which the science is governed. In our treatment of Geometry (which is, after all, but a branch of Mensuration) we have explained what are the relations, proportions, and properties of lines and surfaces. Under the head of Mensuration we shall show the mode of estimating the lengths, surfaces, and capacities formed by lines and angles. And herein lies the difference between the two subjects, for whilst Geometry simply treats of the general relations of lines and angles, Mensuration enters into the methods for determining their length and extent in individual cases.

In order to avoid repetition, we will refer our readers to our chapters upon Geometry for the definitions which are necessary to be understood in studying the subject of Mensuration.

It will strike every person upon reflection that all measurements must be included under four distinct heads: the first, of lines; the second, of angles, that is, of the inclination of two lines to each other which meet; the third, of surfaces, that is, of spaces included or shut in by lines, but devoid of thickness; and the fourth, of solids, that is, of bodies possessed of length, breadth, and thickness. Everything possessed of magnitude can be classed under one or other of these four distinct heads, and we propose to adopt the order in which we have stated them in our consideration of measurements generally.

And first as to lines. The measurement of lines, which at first sight appears a very simple process, is by no means so easy a matter as it appears. We are, of course, speaking not of approximate, but of correct measurement. It is by no means easy to ensure perfect uniformity-undeviating equality-in the length even of the self-same thing. The dimensions of all bodies are affected in a greater or less degree by differences of temperature, and however minute this difference may be, yet when the body or instrument so affected is intended to be used as a standard or guide wherewith to measure other and longer lines, an error, however trifling, becomes speedily doubled, tripled, and so on, until it has grown serious.

Our national standards of measurement are on this account most scrupulously protected, and if required for reference must be used with the greatest caution, particularly as regards temperature.

It is not, however, necessary in the ordinary routine of busi

ness to be so minutely exact as, for instance, to bring a powerful microscope to bear upon the point where the rod, rule, or chain has to repeat itself in order to secure perfect coincidence at the point of meeting. Indeed, in the use of that valuable measurer of length, the Gunter chain-an instrument we shall have again to refer to--a man accustomed to the work will bring its back extremity so nearly to coincide with the point where the front end of the chain last touched, that after many hundred repetitions of the operation, a second measurement by calculation will detect but a few inches of difference.

In measurements of length, when the distance to be measured is trifling, recourse is had to a foot rule, a yard measure, or a ten-foot rod; but in longer distances, the measurement of land for instance, the "Gunter chain" is employed, for reasons which will be explained when we come to treat of land surveying. This chain consists of 100 iron links united by iron rings. The full length of the chain is 66 feet, consequently each link and its accompanying ring is of a foot in length, or 7.92 inches. Every ten links from either end is distinguished by a brass label having one or more notches cut in it, the number of notches corresponding to the number of tens from the end nearest it, and the middle or fiftieth link having a circular piece of brass attached to it. These marks are intended to save time and trouble in counting the number of any particular link from the extremity of the chain.

Another point for consideration in measuring accurately a long line is to guard against any deviation from its intended route. If it be a straight line, the course throughout must be absolutely straight, and to accomplish this it will be necessary either to fix upon a given landmark of small lateral dimensions which lies exactly in the intended line, and to direct each successive extension of the chain upon this point by the eye, from the back end of the chain, or previously to stake out by means of rods the line of route, and to be careful that the chain lies always evenly along that line. In the measurement of a curved line, the rods employed to stake it out must stand sufficiently close together as that an almost inappreciable difference shall exist between the straight lines which connect them and the curve of which they form a part. Correctness in the measurement of lines is absolutely essential to correctness in the measurement of the spaces enclosed by them; this fact cannot be too carefully borne in mind. Our next step is the consideration and measurement of the inclination of two straight lines to each other which meet, that is, of the angle formed by their meeting or intersection. Mensuration in this respect is simply the application of arithmetic to trigonometry. We shall not at present go deeply into the subject of trigonometry, but merely explain the rules upon which the measurement of angles is based.

D

Fig. 1.

B

C

It is proved by geometry that the angles at the centre of a circle bear to one another the same proportion as the arcs, or portions of the circumference of the circle which the lines forming the angles cut off from it.

In Fig. 1, let BCD be a circle of which a is the centre, and let the line AB be drawn, and suppose it fixed. It is evident that, as from the centre of a circle any number of lines or radii can be drawn from the centre to the circumference, we can draw AC, A C' in any position we please, and thus form any number of angles BAC, BAC at the point A. Now the measure of these angles is estimated, not by the lines which form them, as AB, A C, A c', but by the arcs of the circle these lines cut off; thus, the measure of the angle B A C is the arc B C, and so on. It is, therefore, only necessary to adopt some method of dividing these arcs in order to measure arithmetically the angles they represent.

D

A

B

Fig. 2.

Now it has been decided that every complete circle shall be considered as divisible into 360 equal parts, each of these parts to be called a degree; again, each degree shall be divisible into sixty equal parts, called minutes; and each minute into sixty equal parts, called seconds. The division can be carried further, but it is not usual to extend it beyond seconds. The signs by which these several divisions are recognised are:-A degree, by; a minute, by '; and a second,