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which have peopled it in past ages, has been one
with that of the vegetation which has accompanied
them, one with that of man and society which has
in a measure come after them."

That is to say, that in the earliest strata we do
not find remains of such complex organizations
as share the earth with man to-day, and whose
structure is more or less allied to his own; nor, as
we have said, do we find there either a vegetation
with that wonderful diversity of form and colour
which delights, and in delighting educates and
develops the refined and subtle faculties of the
human mind. The whole course of creation has
been one harmony of power and form.

i 1 organization. Aggregations of such cellular bodies iato large wholes is a still further advance. Again, when such wholes have certain individual characteristics, and these individuals are united together to form a compound structure, though still in a greater or less degree leading an independent life as in sponges, we speak of such community as forming an organism higher in the scale than the others. Those little societies of monads or cells, whatever else we may call them, are societies only in the lowest sense; there is no subordination of parts among them-no organization. Each of the component units lives by and for itself, neither giving nor receiving aid. There is no mutual dependence save that consequent on mere mechanical union."* Even when this "mixed jelly" or these cells constitute an organism, which we may safely call an individual, there is little of that structure which we usually associate with the idea of an animal. Now, here it may be well to remark that, although a strict definition of the terms higher and lower, and the application of them first to classes, and then logically to different individuals of these classes, lead us into strange absurdities and contradictions, yet it is evident we cannot dispense with them. The source of these contradictions we shall explain hereafter. Enough for the present that the common sense of mankind, basing its judgment on the principles which make one society, one human being superior to another, will affirm that the animal kingdom shows us gradations of rank; that a mollusc is higher in the scale than a sea-anemone, that a fish is superior to an oyster, an eagle to a spider, man to a dolphin or a whale. It is for us to indicate scientifically the general grounds of this distinction. We shall find that, in the main, they are the same as establish the difference between the orders of the vegetable kingdom, as also between the higher and lower social organism.

When we examine the body of one of those compound polyps common to our ponds, we find a mere jelly-like sac in which there is great uniformity of structure; in which, as we have said, the outer tissue may perform the functions of the inner one, and vice versa; in which there is no digestive or respiratory apparatus, no heart, alimentary canal, circulatory or nervous system. We have little or nothing of that which has been aptly termed the physiological division of labour. But when we discover a difference between the internal and external covering, a step towards the development of organs of nutrition and of the apparatus of external action; when we find a duct for the conveyance of blood, a part of the body specially devoted to its aeration, a receptacle for the food, nerves to convey sensations, and to serve as sympathetic bonds between the different members, organs, or parts-thus making the exercise of each subservient to the well-being of the whole-we say there is an advance in the organization. The degree in which we find this complexity of structure, the differentiation of function, these varied phases of activity in any organism, shall be determinative of its rank. Therefore it is that the mollusc is higher than the coral polyp; that, of the mollusca, the cuttle-fish with osseous skeleton, with large eyes, strong muscles, a complicated digestive apparatus, and a well-developed brain, is higher than the snail or oyster; that the articulata, as a rule, are superior to the mollusca; that spiders, lobsters, crabs, bees, &c., are higher than whelks and limpets.

In that vast series of ages during which the strata which now form the dry land of the earth were gradually and slowly deposited by the waters, and then raised above the surface of the deep, epochs of greater or less duration have distinguishing characteristics.

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it is the presence of his remains, or of his productions that now first find a place-have a genesis also and a becoming-in the evolution of that great organism of which he is a part. Considering then such development as we have here indicated; the insensible gradation by which life has attained to its present wide discourse;" how the inorganic has passed into the organic, mere sensibility to impression into instinct, instinct into intelligence, intelligence into moral ideas, and brute force into delicate organization; how the epochs of the geologist blend with one another, yet possess distinctive features, how the forms which characterize them, widely different as some of them are, may yet be traced back to a similar ancestry; how the lifeenergy of the world has thus fashioned for itself one language and one history, we cannot be insensible to the analogy which is suggested by it. The creative and productive energies of nature have stamped each epoch with a particular character, and that character is more complex as the years advance. Looking at the animal life of the world in its totality, its progression is analogous to that of an individual. Taking also the whole of its vegetable life, a similar unity in the plan of development is presented to us. That advance, from the simplest structures of the Laurentian and Cambrian rocks to the varied diversity of the vegetation of the present era, is typified in the growth of every tree in the forest. Protoplasm into cells, cells into folia, folia into axes, axes into branch-combinations-such in brief are the stages passed through by every shrub; and such appear to have been the stages through which plants of successively higher kinds have been evolved from lower kinds.'

The systems of the geologist which denote these epochs, commencing with the earliest that were formed and ending with the more recent, are termed the Cambrian, Silurian, Devonian, Carboniferous, Triassic, Oolitic, Cretaceous, and Tertiary. Now let us glance at the forms of animal life which successively characterize them.

Look again at the simple starchy mass whichi s the substance of the acorn, and notice the changes which it undergoes. When the influences of heat and light have initiated changes in its molecules, it is not a leaf or flower which is produced; the progress to these is so gradual that we cannot perceive where one state begins and another ends; when the germ is no longer a germ, but plumule and radicle; when the outer tissue of the former begins to assume the appearance of bark; when the first rudiment of the leaf is formed, and when the structure of the roots diverges from the stem. Neither in the evolution of the whole vegetable kingdom can we perceive where the specific characters of one individual class or species begins, nor where, indeed, their influence ends. Vegetable progress, like all other, is continuous, is cumulative. Myriads on myriads of individuals have lived and died, and each has passed on to its successor the advantage it gained. The life of a large tree is a cycle involving other cycles. Each returning spring sees the renewal of its life, the summer its maturity, the autumn its decay. So has the vegetation of the earth, as a whole, had its period of commencement, its exuberant growth, and also its decline. But not only individuals, but vast groups of these, different species and genera, have had their genesis, have gradually attained their highest organization, their greatest perfection, become for a while the dominant forms of the plant-life of the earth, and then gradually disappeared. So have flourished and passed away, for instance, many of the species which form, in a great measure, our coal-beds.. They have now no representative in existence.

Wheresoever we find the primary rocks, whether
in the Ural mountains, in those of Wales or of
Canada, in the Steppes of Russia or in the far
west of America, there it is that the early traces of
life commence in the coral-like masses formed by
those microscopic animalcula which we take to be
the lowest form of animal existence. Shells also
of such minute and simple organisms as are at
present found in the ooze of the sea, or amidst its
waters. Later, we come to shells of the lower
molluscs; crustacea analogous to the embryo-
logical forms of species which succeed them; the
rocks occasionally reveal to us also the tracks and
burrows of worms. But the evidences of life are
yet somewhat scanty. The organisms themselves
were perishable. The action of fire on the strata
has more or less metamorphosed them. In the
Silurian epoch, the aspects of life broaden; although
the remains of no terrestrial animal have yet been
discovered in it, sponges, corals, starfishes, higher
molluscs and crustaceans abound. With the Devonian
era we enter upon the predominance of gigantic
crustaceans with complex limbs, and a corre
spondingly complicated internal economy; but,
above all, it is here that we meet with fishes
for the first time. Shoals of them are imbedded
in the strata, albeit of so simple a type of
structure as to have been mistaken for crustaceans,
and even huge water-beetles. In the Carboniferous,
many of the lower forms of life already noticed
have become more complex; their different species
have more determinate and distinctive forms. The
bone-encased fishes of the Devonian have given
place to forms analogous to some which now are
found in Australian seas. With the dry land which
now seems to become more general, and the growth
of the vast forests which at present afford us coal,
the remains of beetle-like insects are discovered.
Evidences of terrestrial life are also furnished by
fish-like lizards, frog-like reptiles, and a linking and
blending of aquatic and terrestrial life as manifested
in the characters of Amphibia. In the Permian
and Triassic systems we find true lizards and true
reptiles abundant-some species of huge size and
When the osseous skeleton which we have noticed of high organization. At the same time, the general
in the cuttle-fish divides the body into two cavities, character of the forms of life contemporaneous
one of which is specially adapted to the organs of with them has altered. The molluscs present greater
nutrition and the other to the principal nerve- differences, the bone-encased fishes of the Devonian
centres, with all the wonderful modifications such age have given place to others more resembling
division implies, we have the vertebrate type of those now existing. Insects are more varied. We
structure. This is an advance on the others, one have yet no evidence of true birds, but only of rep.
which makes fishes, as a class possessing it, higher tiles walking bird-like on their hind feet; none of
than insects, molluscs, and protozoa. Now a land true mammals, but only of those which produce
animal being subject to greater differences of con- their young in so imperfect a state that it has been
ditions than one which inhabits the sea, will, as a well said that it is a shell-less egg that is born-it
rule, have corresponding differences in its struc- is marsupial-like animals, such as are allied to the
ture, the limbs will be more diverse in their kangaroo, which precede the true mammals. In
character, organs of nutrition adapted to more com- the Oolitic, reptiles abound to such an extent,
plex nature of food; lungs with their myriad wade through the marshes, swim on the sea, fly
interstices will have replaced gills; the blood will over the land, that it has been termed par excel-
be warmer, the machinery for propelling it more lence the age of reptiles." Traces of true birds
complicated; the senses more acute, nerves more also become noticeable towards the close of this
intricate, brain more developed. It is therefore
that an amphibian is superior to a fish. On the epoch. But in the chalk these indications became
more frequent, and here also are signs of the exist-
same principle of more complex organization,
reptiles as a class present to us a higher type than epoch, while vast numbers of species which charac-
ence of true mammals. But with the Tertiary
amphibians, birds than reptiles, and a man, as terized the preceding ages have become extinct,
representative of the mammalia, has an organism others take their place become as it were the domi
decidedly more complicated as a whole than any bird. nant and special forms of existence. It is here that
However much we may be at a loss when we the birds whose gigantic remains form the curiosi-
consider all the details of the vast scheme of life ties of our museums-the Epiornis of Madagascar,
that has been developed on the earth; however the Dinornis of New Zealand-come on the scene;
much the facts of geology, or more properly it is here that enormous mammals, as the Megathe
paleontology, limited as they are, may seem to rium and Mastodon, are first discovered. The whole
contradict some of our notions with regard to it; of creation has been gradually assuming the aspect
small as is the portion of the earth's crust that has it presents to us now. In the Tertiary strata, we per-
been explored, or looking at the vast expanse of ceive how plant, molluse, fish, bird, mammal are be-
water on the globe, ever will be subject to the coming more and more like the forms they exist in to-
scrutiny of science, enough has been discovered to day. Myriads on myriads of individuals, nay thousands
show us that "the law of the genesis and becoming of species arise and decay; only those forms abide
of the living forms which people the world now, and which are compatible with the general character of
the world's advancing life-which are one with that
which slowly culminates in man; for
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*H. Spencer, "The Social Organism," Essays. Vo. I. great

(To be concluded next week.)

MECHANICAL MOVEMENTS.

(Continued from page 488.)

280. A, has permanently secured within it a central tube a, which slides on a fixed tube 6 in the centre of the tank.

Another kind of gasometer. The vessel

The

281. Wet gas meter. The outer case is stationary, and filled with water up to above the centre. inner revolving drum is divided into four compartments, B B, with inlets around the central pipe a, which introduces the gas through one of the hollow journals of the drum. This pipe is turned up to admit the gas above the water, as indicated by the narrow near the centre of the figure. compartments B B, one after another, it turns the drum in the direction of the arrow shown near its chambers pass over they fill with water again. The periphery, displacing the water from them. As the cnbic contents of the compartments being known, and the number of the revolutions of the drum being registered by dial work, the quantity of gas passing through the metre is registered.

As gas enters the

282. Gas regulator (Power's Patent), for equalizing the supply of gas to all burners of a building or appartment, notwithstanding variations in the pressure on the main, or variations produced by turning gas on or off, to or from any number of the burners. The regulator-valve, D, of which a separate outside view is given, is arranged over inlet pipe E, and connected by a lever, d, with an inverted cup, H, the lower edges of which, as well as those of valve, dip into channels containing quicksilver. There is no escape of gas around the cup H, but

Principles of Biology," vol. ii., p 214.

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there are notches, b, in the valve to permit the [vented from turning back by a pawl attached to its gas to pass over the surface of the quicksilver. As lower part and working in a circular ratchet on the the pressure of the gas increases, it acts upon the base. inner surface of cup H, which is larger than valve, and the cup is thereby raised, causing a depression of the valve into the quicksilver, and contracting the opening notches b, and diminishing the quantity of gas passing through. As the pressure diminishes an opposite result is produced. The outlet to burners is at F.

283. Dry gas meter. Consists of two bellows-like chambers, A A1, which are alternately filled with gas and discharged through a valve B, something like the slide valve of a steam engine, worked by the chambers A A1. The capacity of the chambers being known, and the number of times they are filled being registered by dial-work, the quantity of gas passing through the metre is indicated on the dials. 284. A spiral wound round a cylinder to convert the motion of the wind or a stream of water into rotary motion.

285. Common windmill, illustrating the production of circular motion by the direct action of the wind upon the oblique sails.

286. Plan of a vertical windmill. The sails are so pivoted as to present their edges in returning towards the wind, but to present their faces to the action of the wind, the direction of which is supposed to be as indicated by the arrow.

287. Common paddle-wheel for propelling vessels; the revolution of the wheel causes the buckets to press backward against the water and so produce the forward movement of the vessel.

288. Screw propeller. The blades are sections of a screw-thread, and their revolution in the water has the same effect as the working of a screw in a nut, producing motion in the direction of the axis and so propelling the vessel.

289. Vertical bucket paddle-wheel. The buckets, a a, are pivoted into the arms, b b, at equal distances from the shaft. To the pivots are attached cranks, ee, which are pivoted at their ends to the arms of a ring, d, which is fitted loosely to a stationary excentric, e. The revolution of the arms and buckets with the shaft causes the ring, d, also to rotate upon the excentric, and the action of this ring on the cranks keeps the buckets always upright, so that they enter the water and leave it edgewise without resistance or lift, and while in the water are in the most effective position for propulsion.

290. Ordinary steering apparatus. Plan view. On the shaft of the handle-wheel there is a barrel on which is wound a rope which passes round the guide-pulleys and has its opposite ends attached to the "tiller" or lever on the top of the rudder; by turning the wheel, one end of the rope is wound on and the other let off, and the tiller is moved in one or the other direction, according to the direction in which the wheel is turned.

291. Capstan. The cable or rope wound on the barrel of the capstan is hauled in by turning the capstan on its axis by means of hand-spikes or bars inserted into holes in the head. The capstan is pre

292. Boat-detaching hook (Brown & Level's). The upright standard is secured to the boat, and the tongue hinged to its upper end enters an eye in the level which works on a fulcrum at the middle of the standard. A similar apparatus is applied at each end of the boat. The hooks of the tackles hook into the tongues, which are secure until it is desired to detach the boat, when a rope attached to the lower end of each lever is pulled in such a direction as to slip the eye at the upper end of the lever from off the tongue, which being then liberated slips out of the hook of the tackle and detaches the boat.

293. "Lewis," for lifting stone in building. It is composed of a central taper pin or wedge, with two wedge-like packing-pieces arranged one on each side of it. The three pieces are inserted together in a hole drilled into the stone, and when the central wedge is hoisted upon it wedges the packing-pieces out so tightly against the sides of the hole as to enable the stone to be lifted.

294. Tongs for lifting stones, &c. The pull on the shackle which connects the two links causes the latter so to act on the upper arms of the tongs as to make their points press themselves against or into the stone. The greater the weight the harder the tongs bite.

295. Entwistle's patent gearing. Bevel-gear, A, is fixed. B, gearing with A, is fitted to rotate on stud, E, secured to shaft, D, and it also gears with bevel-gear, C, loose, on the shaft, D. On rotary motion being given to shaft, D, the gear, E, revolves around A, and also rotates upon its own axis, and so acts upon C in two ways, namely, by its rotation on its own axis and by its revolution around A. With three gears of equal size, the gear, C, makes two revolutions for every one of the shaft, D. This velocity of revolution may, however, be varied by changing the relative sizes of the gears. C is represented with an attached drum, C'. This gearing may be used for steering apparatus, driving screw-propellers, &c. By applying power to C, action may be reversed, and a slow motion of D obtained.

296. Drawing and twisting in spinning cotton, wool, &c. The front drawing-rolls, B, rotate faster than the back ones, A, and so produce a draught, and draw out the fibres of the sliver or roving passing between them. Roving passes from the front drawing-rolls to throstle, which, by its rotation around the bobbin, twists and winds the yarn on the bobbin.

297. Fan-blower. The casing has circular openings in its sides through which, by the revolution of the shaft and attached fan-blade, air is drawn in at the centre of the casing, to be forced out under pressure through the spout.

298. Siphon pressure gauge. Lower part of bent tube contains mercury. The leg of the tube, against which the scale is marked, is open at top, the other

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leg connected with the steam-boiler paratus on which the pressure is to The pressure on the mercury in the it to be depressed in that and raised in the the until there is an equilibrium established between the weight of mercury and pressure of steam 1 ** leg, and the weight of mercury and pressure of atmo sphere in the other. This is the most accurate a known; but as high pressure requires so long tube, it has given place to those which are pr cally accurate enough, and of more convenie (To be continued.)

WROUGHT-IRON CRANES-Z
(Continued from page 4

N our last article on this subject the solid-sided or plate-web crane was the example selected for illustration and description. Its merits pointed out, and its disadvantages also tigated. Before proceeding to determine the and extent of the strains that act upon a c will briefly notice the constructive differen exists between the open and the solid web To avoid needless repetition, and not to intru more cuts than are necessary, we will assume the the duty required of the crane is sufficiently to necessitate that it should be of the double we type-in fact, an open-sided tubular crane. It v be at once seen that while this form possesses the advantages with respect to stiffness that given by the solid-sided form it is also free from disadvantages. There is no difficulty in examining every part of it, and painting and repairing it when necessary. In Fig. 1 is represented the elevation

FIC.I

of a lattice bent crane with a double series of triangles in the web. Frequently the crane has a web of the Warren type, in which there is but one system or series of triangles, but the arrangement of the number of series depends altogether upon the size of the crane, and especially of its depth. The deeper the web, the greater must be the num ber of intersections of the bars, or the greater must

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e the amount of stiffness given to them, either by
creasing the sectional area of metal in them, or
dopting a form of section adapted to ensure the
equisite rigidity. It will be at once apparent that
he greater the number of the crossings of the bars
1e less becomes the actual length of any unsup-
orted bar. Every intersection of two bars, sup-
osing it to occur at the middle of their respective
ngths, virtually reduces those lengths one-half,
nd the stiffness of the bars is thus nearly doubled,
or while the original strain remains the same, the
endency of the bars to deflect is very considerably
iminished. This was one of the causes that
peedily proved how deficient the Warren system
ras in those points when girders of large span
rere proposed to be constructed on that principle.
t was soon discovered that it was absolutely im-
bossible to construct a deep girder with only one
series of triangles. The amount of material that it
was necessary to introduce in order to afford the
proper degree of stiffness to the bars was very much
in excess of that which would be required in a solid
sided or plate girder. It must be borne in mind
that the superior economy of the open or lattice
type of girder over that of the plate system rests in
the web, and in the web alone. The flanges or
horizontal members of both systems are nearly
identical. If, in designing a large girder on the
lattice principle, the saving is not effected in the
web, it cannot be obtained in any other part.
The section of the crane shown in elevation in
Fig. 1 is represented in Fig. 2, and, with the excep-

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IT

the other bars. But this is not sufficient, and THE FORECASTING OF STORMS.*
it becomes necessary to adopt a form of section
that by virtue of its own shape shall possess some
cannot be denied, that the complicated and
degree of inherent stiffness and rigidity. Inde- constantly varying phenomena of that fickle
pendently of this reason there is another. It is entity which we denominate the weather form a
that although the intersections of the bars do problem which in the nature of things must be ex-
contribute to the stiffening of the web of the girder, tremely difficult of solution; and it is hardly pro-
yet they are not supposed to actually prevent the bable that any man will ever be able in this field of
bar from deflecting. There is little doubt that they inquiry to reach the same satisfactory results that
in reality do so, but it must not be taken into have rewarded the labours of the astronomer. It is
account when proportioning the bars, because it is a source of legitimate pride to Americans, however,
always assumed that there is no extra strain brought that in two important departments of meteorologi-
upon the respective bars by their being riveted or cal investigation citizens of this country hold the
bolted to one another. It is at the same time first rank. To Dr. Franklin belongs the honour of
manifest that if they were prevented from deflect- discovering and elucidating the principles of elec-
ing, in consequence of the points of intersection, tricity, and of demonstrating the influence of that
there would be a considerable transverse strain subtle force upon the earth and its atmosphere;
induced upon them. This strain, which would and it was Redfield who, something like a century
increase with the length of the bar, would altogether later, deduced from his own careful observations
vitiate the whole principles of girder construction, of storms upon our Atlantic coast the important
as we have already frequently explained in our generalization that there is a class of great storms
columns.
which originate near the equator, in the region of
The form selected for the compression bars in the West Indies, and rapidly advance, according to
Fig. 2 is that of angle iron, but there are several a fixed law, with a simultaneously gyratory and
other forms equally suitable. Of these, tee or progressive motion, upon a well-defined curved axis
channel iron is to be preferred, but they all yield towards the north pole. These storms vary greatly
to angle iron in simplicity and facility for attach-in intensity and in breadth-sometimes being con-
ment. Moreover, the last description of section is fined to a narrow belt upon or a little way off from
that most readily procurable in the market. It can the coast, and again extending over a wide expanse
always be obtained of the usual scantlings at a very of land and sea; but that they uniformly follow the
moderate price per ton, whereas some of the other same general course indicated by Redfield has been
sections are only to be obtained by special order, abundantly established by a great number of sub-
thus entailing a long delay, and sometimes are not sequent observations. It is not designed here to
to be had at all. There is no greater mistake made enter into an elucidation of this important law, but
than to design a structure with a quantity of im- attention is called to it as marking one of the few
possible-shaped material in it. As a rule, always real and tangible and practical achievements in the
select those forms, sections, and sizes of iron that field of meteorological science. Its discovery and
are the most readily obtained, and at the most announcement stimulated investigators both here
moderate cost. It is not only the shape of the iron and in the Old World to renewed energy in their
that is of importance, but the dimensions. When efforts to unravel the mysteries of atmospheric
bars beyond a certain length in one piece are phenomena. The subject of storms, both ocean and
wanted, or plates containing more than a certain inland, was especially studied with quickened zeal
maximum superficial area, there is an extra price and enthusiasm: and in due course of time an at-
per ton charged. Thus, a narrow plate of about tempt was made abroad-first in England, then in
12in. broad can be procured at the ordinary market France, and afterwards in other continental coun-
prices in a considerably longer single length than tries to utilize the knowledge gained thereby in
the interests of commerce, which, ever since it
has existed, has been subjected to constant peril
and loss from the effects of storms. The prevailing
courses of the most destructive storms in various
localities having been definitely ascertained, mea-
sures have been taken to give warning to exposed
points of their approach, by means of the telegraph.
This intelligence being promptly communicated by
preconcerted signals to all vessels passing within
sight of the shore or lying at anchor in harbour or
roadstead, such vessels are enabled to take all
necessary precautions against disaster before the
storm shall burst upon them; and immense damage
to shipping has thus in very many instances been

one of 24 or 30in. in breadth.

At the time of constructing the Britannia Tubular
Bridge over the Menai Straits there was the
greatest difficulty experienced in obtaining plates
12ft. in length. Since that time our iron manu-
facture has made a great deal of progress, but still
long plates are very expensive. This is owing to a
combination of many circumstances. In the first
place, the larger the plate the greater the trouble
and expense of handling and transporting it from
one place to another. Secondly, the difficulty of
rolling a plate or bar that shall be homogeneous
in consistency increases enormously in proportion
to an increase in the size; and thirdly, larger and
more expensive rolling machinery is necessary than avoided.
for plates and bars of the ordinary dimensions.
Besides stiffening the bars in the web of the bent
crane in the plane of the elevation of the crane,
they also require some bracing in a plane at right
angles to the face of the web. The opposite bars
have to be braced together transversely, as shown
in Fig. 2. This is usually effected by introducing
small pieces of bar or angle iron, and riveting them
(see A A, in Fig. 2) to the diagonals at their inter-
sections with each other.

In large examples, the opposite diagonals are
united, not merely by horizontal pieces of bar, but
by a regular system of cross bracing, so as, in fact,
to convert the whole couple of diagonals into a
small braced girder of itself. Wherever the depth
of the girder is small this is not needed, but the plan
shown in Fig. 2 will afford all the security required,

tion of the web or sides, does not differ materially
from that given in our last article. Directly the
horizontality of the flanges is departed from the
strains upon the bracing or bars connecting the
upper and lower flanges, and constituting the web,
become very complicated, and it is by no means
easy to ascertain, without some slight consideration,
which of them act as struts and which as ties.
When we proceed to analyze the strains upon a
bent crane, and the manner in which each separate
bar is affected by the load, it will be demonstrated
that those which slope towards the lower or fixed
extremity of the crane are subject to compressive
strains, and, per contra, the others to those of a
tensile description. But this is not a universal rule,
for a great deal depends upon the radius of the
upper and lower flanges, the depth of the web, and
the angle of inclination of the bars. This angle is
continually changing, which is the great impedi-
ment to the use of mathematical calculation for
these examples of construction. In those instances
where the flanges, both upper and lower, are hori-
zontal and parallel to one another, the angle of all
the diagonal bars is constant, and the calculation
of the nature and amount of the strains may be
effected either by geometrical diagrams, or by
simple and readily deducible formula. But directly
either or both of the flanges assumes a curvilinear
outline this simplicity of calculation is at once lost.
The ordinary formulae are no longer applicable, and
those that would theoretically apply to each par-
ticular case in question are so exceedingly trouble.
some, complicated, and uncertain, as to be prac-
tically useless. It is not too much to assert that to
attempt to employ algebraical or mathematical
equations and formule to some of the examples of
girder construction would be to attempt a practical
absurdity. Recourse is therefore had to the gra-
phical method, and by means of a diagram of strains
the proportions of the several parts can be accu-
rately determined. At present we are not concerned
with this part of the subject, which will be fully
discussed in a subsequent article.

We must reserve for the next article on the

subject the investigations into the strains upon
these braced specimens of construction.-Building
News.

contact.

Notwithstanding the salutary operation of this system abroad, however, and notwithstanding the peril from storms to which our commerce on the great lakes and the Atlantic seaboard is constantly exposed, no measures have been taken in this country, until within the past few months, for the inauguration of such a system here. Early in the present session of Congress, however, the matter was brought to the attention of the House of Representatives by the Hon. Halbert E. Paine, of Wisconsin, who offered in that body a joint resolution providing "for taking meteorological observations at the military stations and other points in the interior of the continent, and for giving notice on the northern lakes and seaboard of the approach and force of storms." The resolution in full is as follows:

"Be it resolved by the Senate and House of Representatives of the United States of America in Congress assembled, That the Secretary of War be, and he hereby is, authorized and required to provide for taking meteorological observations at the military stations in the interior of the continent, of the United States, and for giving notice on the and at other points in the States and Territories northern lakes and on the sea-coast, by magnetic telegraph and marine signals, of the approach and force of storms."

This resolution was promptly passed by both houses of Congress, and on the 9th of February, By General Orders No. 29 from the head-quarters 1870, became a law by the approval of the President. of the army, dated March 15, 1870, the chief signal officer of the army, Brevet Brigadier-General A. J. Myer, is charged, subject to the direction of the visions of this enactment, and all commanding Secretary of War, with the execution of the proofficers are enjoined to afford every facility for the successful prosecution of the undertaking; while

old method of cauterization by fire is to be replaced by USE OF ELECTRICITY IN CAUTERIZATION.-The the electro-thermic or galvano-caustic apparatus. The latter process is safer and more certain in its operation. It is possible at will to vary the degree of heat, to raise it instantly to the highest intensity, to diminish or suppress it, to render it intermittent or continued, to direct it into deep cavities, and to destroy all the tissues by electricity are less liable to contagion and miasmatic inIt is said that the wounds produced by fections than those caused by sharp instruments. The apparatus can be made of any desired shape so as to be applicable to all parts of the body, and it is known that important cures have been effected by the introduction of parts of the body inaccessible in any other way. of platinum wires and the cauterization by the battery Electricity has already been tried in cases of bad tumors, in amputations, in excisions of cancers, in destruction of wens, for opening cysts, for removing internal tumors, cent article in Cosmos claims for it the following adupon wounds by fire, and in numerous other cases. Ascientific establishments, commercial associations, A reference to Fig. 2 will show that a plain bar vantages: The electro-thermic cautery suppresses all section will not answer for the compressive bars the retention and alteration of the liquids; avoids all pain after the operation; avoids loss of blood; prevents in the web of a bent crane. This is owing to the putrid and purulent infections; facilitates the organic fact that a plain rectangular bar has little or no reconstruction and healing of the parts; affords a lateral stiffness. It is true that when occupying method universally applicable, strong or weak, conthe position of one of the diagonals in the web of tissues, of carbonizing them, of destroying them, of continuous or intermittent; capable of sloughing the a girder designed on the lattice principle, it is verting them into gas, and must be regarded as one of stiffened to some extent by the intersections with the most important contributions to modern surgery."

and others, are requested to aid, by their co-operation, in the accomplishment of the work.

by the frightful aggregate of a single year's disasters Professor J. A. Lapham, of Milwaukee, impressed to vessels on the great lakes-amounting for the year 1869 to the immense number of 1,914, with an estimated damage to property of over four millions

Extracted from an article by L. A. ROBERTS in the Western Monthly.

of dollars-was perhaps the first to suggest some down, crushing the horses and burying himself to Unless this adhering layer of air is p action by Government for inaugurating such a the middle in its debris-and there he stands, up- cement cannot adhere to the surface to PL ! system of storm-reporting as, through the efforts right, stark dead in an instant! A little farther applied simply because it cannot come we of General Paine, has now happily been adopted. down the street an unfinished frame building goes with it. The most efficient agent in ope It should be remarked that by no means all of the down even before the workmen upon it can reach air is heat. Metals warmed to a pointi disasters included in the aggregate above given the ground, and three men are crushed in the mass 200°, become instantly and completely 7.were of that class which might have been obviated of timbers and escape death by a miracle. mersed in water. Hence for cements 15 by the operation of the system we are considering. All this, and vastly more, in one little village; in a fused condition, heat is the most Very many were due to imperfect machinery, and a dozen villages are in the track of the monster. of bringing them in contact with the defective boilers, careless collisions, conflagrations, Ay, a monster he is, and almost insatiable, but not which they are to be applied. In the 2 and other causes. Yet, making all proper deduc- quite; for right in his course stands a little country- the adhesion is best attained by mo tions on this score, enough remain to be attributed house, the inmates of which, looking westward, and friction. Another very important... to the destructive force of severe and unheralded hear his roar and see him come crashing through a as little cement as possible. When t storms, to fully justify any action by Government belt of woods a quarter of a mile away. They make separated by a large mass of cement = * looking to a mitigation of the destruction of such hasty preparations as they can for the impend-pend upon the strength of the cemer @ property and the peril and often loss of life which ing catastrophe; but, to their utter astonishment, not upon its adhesion to the surface they entail. No corresponding statistics are at they find in a minute or so that the storm has used to join; and, in general, cements any hand as to the yearly disasters upon our Atlantic passed them by unharmed and is tearing through tively brittle. seaboard; but these are very numerous, as is well the woods to the east of them. This characterknown, and of these a much larger proportion than istic of these tempests has been often observed. of the lake disasters are attributable to the agency While in general they move upon the ground, of storms. Besides the great equatorial storms sweeping it clean as they go, occasionally they rise already alluded to, which in their course towards above it, and again descend-bounding, as it were, the pole follow approximately the coast-line of the like an india-rubber ball that has received a superior United States, our coasting vessels are likewise ex-ground stroke from the champion batter of a "firstposed to frequently-recurring tempests, especially nine." in the summer season, which originate probably upon the great desert basin in the interior of the continent, and, sweeping eastwardly across the Mississippi Valley and the great lakes, expend their final fury upon the ocean and its navigators.

Nor must we overlook the damage often worked

on land, as well as upon the water, by these latter storms, and by those tornadoes of narrower limit and shorter duration, but often of even greater intensity, which prevail at intervals throughout the Mississippi Valley, and lay waste the narrow belt of country which they traverse. Of this class was a storm which swept through Northern Ohio and on the Alleghany Mountains in Pennsylvania in the summer of 1855, demolishing very many buildings in its course, uprooting trees and razing fences, and causing the death of many persons. So furious was this storm, and yet of so limited a breadth only about an eighth of a mile-that while in some villages over which it passed scarcely a house escaped damage, in others only the northern or southern section of the town would be devastated; the outer verge of the destructive force being so sharply defined that while one house, that fell within its track, would be almost totally destroyed, another, but a few yards distant, would be wholly unharmed. The course of this storm may even yet be easily traced in the forests through which it raged. It cut a clean swath as it went, leaving openings that look as if they had been cleared for a highway or a railroad. The timber thus prostrated was in some cases utilized for firewood or for lumber; but in many places the trunks of the trees were left in such inextricable confusion and tangle-having fallen in every conceivable direction, and being in some instances individually twisted into splinters, as a result of the rotary action of the storm-that it was found inexpedient, in a country where timber was in plenty, to attempt to "pick up the pieces;" and thus the logs were left to rot and replenish the earth. And now, throughout these storm-openings in the woods, vast thickets of the highbush blackberry have grown up; and so we have, as the latest result of that furious tempest, an almost unlimited abundance yearly of the finest blackberries anywhere to be found.

No one who has witnessed such a storm as this will ever forget it. The imminent peril of a storm at sea may be greater and more appalling; but nothing can be more exciting than one of these fierce whirling tornadoes, accompanied, as they almost always are, by a deluge of rain and an almost constant rolling of thunder and glare of lightning. The storm is heralded by a heavy mass of cloud in the west or southwest, dark, with a sulphurous tinge, over the face of which there is an almost constant play of lightning, and within an ominous muttering of thunder. Then there is a dash of rain, a moaning of the wind, and the next moment the storm bursts upon you. Then the air is full of a tumult of unwonted sounds. Loose shutters, sign-boards, and what not, are dashed against the house. Chimneys are blown into individual bricks, and the bricks come clattering down the flues. Doors and windows are burst open; the house trembles to its foundations; and the next moment you behold your roof following your neighbour's in a wild flight for the open countrygoing to pieces as it is borne along like a wreck upon the sea-scattering its fragments broadcast, some of them being found afterwards miles away. Such unfortunate persons as chance to be abroad upon the streets when the fury of the tempest is let loose, strive in vain to make headway either with or against the current, and can do no better when blown to the ground than lie prone there and thank their stars if nothing more pitiless than the drenching rain shall fall upon them; for factory chimneys and church spires go down like grass before the mower, and walls are falling on all hands. One poor man, seeking to rescue a span of valuable horses that are hitched to leeward of a house wall that he fears may fall, is too late; for even while he is in the act of antying the halter the wall is

(To be concluded next week.)

CEMENTS AND HOW TO USE THEM.

A GREAT deal has been written concerning

different cements, and indeed our periodicals are full of recipes on this subject. But it will be found that the information given is rather in regard to the materials used in compounding these cements than in regard to the manner of using them. And it is unquestionably true that quite as much depends upon the manner in which a cement is applied, as upon the cement itself. The best cement that ever was compounded would prove entirely worthless if improperly applied. We have hundreds of recipes for glues, pastes, and cements of different kinds, and yet the public is constantly on the qui vire for new ones, and no more acceptable recipe can be sent to our popular journals than one for a new cement. Now, the truth is, that we have cements which answer every reasonable demand, when they are properly prepared and properly used. Good common glue will unite two pieces of wood so firmly that the fibres will part from each other rather than from the cementing material; two pieces of glass can be so joined that they will part anywhere rather than on the line of union; glass can be united to metal, metal to metal, stone to stone, and all so strongly that the joint will certainly not be the weakest part of the resulting mass. What are the rules to be observed in effecting this?

The first point that demands attention is to bring the cement itself into intimate contact with the surface to be united. If glue is employed, the surface should be made so warm that the melted glue will not be chilled before it has time to effect a thorough adhesion. The same is more eminently true in regard to cements that are used in a fused state, such as mixtures of resin, shellac, and similar materials. These matters will not adhere to any substance unless the latter has been heated to nearly or quite the fusing point of the cement used. This fact was quite familiar to those who used sealing-wax in old days. When the seal was used rapidly, so as to become heated, the sealing-wax stuck to it with a firmness that was annoying-so much so that the impression was in general destroyed-from the simple fact that the sealing-wax would rather part in its own substance than at the point of adhesion to the stamp. Scaling-wax, or ordinary electrical cement, is a very good agent for uniting metal to glass or stone, provided the masses to be united are made so hot as to fuse the cement, but if the cement is applied to them while they are cold it will not stick at all. This fact is well known to those itinerant vendors of cement for uniting earthenware. By heating two pieces of delf so that they will fuse shellac, they are able to smear them with a little of this gum, and join them so that they will rather break at any other part than along the line of union. But although people constantly see the operation performed, and buy liberally of the cement, it will be found that in nine cases out of ten the cement proves worthless in the hands of the purchasers, simply because they do not know how to use it. They are afraid to heat a delicate glass or porcelain vessel to a sufficient degree, and they are apt to use too much of the material, and the result is a failure.

The great obstacles to the junction of any two surfaces, are air and dirt. The former is universally present, the latter is due to accident or carelessness. All surfaces are covered with a thin adhering layer of air, which it is difficult to remove, and which, although it may at first sight appear improbable, bears a relation to the outer surface of most bodies different from that maintained by the air of a few lines away. The reality of the existence of this ad. hering layer of air is well known to all who are familiar with electrotype manipulation. It is also seen in the case of highly polished metals, which may be immersed in water without becoming wet.

THE

CARBON PRINTING ON ENAMEL
AND PORCELAIN SURFACI
HE production of a carbon opaloty-
bably one of the easiest feats in plc,
printing of any kind. Not so, bower!
printing on a rounded or convex surface, ←
enamel tablet of the usual kind. This is a
with some difficulties, but they are not of
nature as to prove insurmountable: more a
extreme beauty of a picture on a convex ei
almost any moderate amount of labour in ore
overcome them successfully. To do this e
modifications in the process are requisit.
first and most important one is to procure a 2-
much more flexible than any hitherto in us:
by flexibility we do not here allude to the gelatin.
sensitive film itself, but to the paper 2.
employed as a means of support for that ght?
The commercial tissue that we have hitherto bera
using in our experiments has a hard, stif paper i
its foundation, and if tried for the parpuse let
proposed will require more than ordinary
ensure a successful result.

surface is such a to just the expenses

When trying some experiments with a red writing of the present article, we made s on a basis of thin and imperfectly-csi m Whereas the ordinary commercial tissue hard and brittle as to admit of its being brot, this, although when dry still stiff and arveling. was devoid of brittleness, and after a brit sing in water became quite limp and flaccid. This is one of the main conditions of success in CANYES out a carbon printing process upon a roma face.

With these explanatory observato proceed to give such instructions as able any careful experimentalist to succes First of all, make a reverse cast the the face of the enamel tablet. This may be rather in gutta-percha or plaster of Paris. Tect of this will be seen as we proceed. Now, having a sheet of sensitized tissue placed on the paper in the darkene room, of course), lay upon it the enamelled table on which it is intended to make the picture, and by means of a penknife or a pair of scissors, pigmented paper to the exact size. Now en this in the printing frame under the negati observe that in the subsequent operations a can be more easily manipulated than if th be printed up to the margin. The reason has already been stated. The pigmented pa being removed from the printing-frame, is cold water, and in the course of a minute becomes quite pliable. It is now laid carefully st upon the enamelled tablet and covered with a of blotting-paper, which ought also to be cut to same size.

The mould of gutta-percha or plaster of whi have already spoken is now carefully laid de upon the top of the paper, which then indies the exact form of the enamel convex surface. is also retained in close contact with it. W very pliable tissue and a very slightly-rounded face, contact may be made by means of the squee but with enamels of the best form this cannot done. In this case, the means we have here describe or some method analogous must be had recourse

When the paper has become partially dry method of development is precisely similar to th recommended in the former article on transparen printing-viz., immerse the tablet first in cold wa for a short time, then in water of nearly the t perature of 100° Fahr., and, after removing paper, continue to allow the hot water to backwards and forwards over the surface every detail be perfectly visible. Now, before picture is allowed to dry, immerse in a weak solnuts of alum, and finally rinse in water and dry. T resulting picture will be quite equal in respect beauty to anything that can be done by burning and at the same time it will be quite as dural! except with regard to mechanical injury.

The brilliancy of the picture is enhanced flowing over the surface some clarified albume and then immersing it in water sufficiently bot coagulate this varnish. We have tried o varuishes-among them amber and chloroformwith good effect.

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EXPERIMENTS ON THE RESISTANCE OF
IRON AND STEEL.*

UNDER this title the author publishes the
results of experiments, made with the
greatest care during a period of twelve years,
which verify his theoretic views upon the laws of
resistance of these materials. We lay before our
readers the author's statement of the laws and their
consequences. He says:-

weight. In large structures it is a general rule
that the limit of elasticity should not be passed.
As a coefficient of safety for repeated vibration,
2 is in all cases sufficient, and in many cases is
higher than necessary.

As a result of his experiments, the author gives
the following table of inch-strains for permanent

structures:

For wrought-iron,
Strained in both directions

For unliaminered cast steel,
Strained in both directions..

80ctr.

paper or glass is fixed upon the upper end of the tube. Heat being applied to the bulb, drives out the air through the mercury, the latter, as soon as the bulb is allowed to cool, descends through the tube, being forced by the pressure of the external atmosphere. The upper end of the tube is then heated and drawn out, ready to be sealed hermeti cally. The mercury is then boiled in the bulb, to expel all trace of air, and while it is in a state of ebullition, the tube is sealed by directing the flame of a blowpipe against the upper end, which fuses the glass and closes the aperture.

,, one direction, total strain. ......180ctr. of which not more than 150 ctr. should be due to the The reader must not imagine that all the manipu variable load. If the constant strain is less than 30 ctr. the permissible total strain must be pro-lations we have described are performed on all thermometers in a perfect and accurate manner. portionally less. A very large majority of these instruments in common use are entirely worthless for any scientific investigation, although they furnish, perhaps, sufficiently accurate indications for the regulation of the temperature of apartments, and for other ordinary purposes.-Scientific American.

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The rupture of material is the consequence of repeated vibrations, none of which reach the absolute limit of resistance. The differences of the MON tensions which limit the vibrations are therefore The ELAN proportional to the disturbance of cohesion. absolute magnitude of the limiting strains is effecofative only as it diminishes the difference attendant beenpon increased strain, which difference causes rup-breaking resistance, if the play of the spring is

d. N. ture. The tensions and compressions affecting the same ed ame fibre are considered as respectively positive and es, but negative; so that the difference of extreme strains is equal to the greatest tension plus the greatest compression.

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.120 ctr.
,, one direction, greatest total
strain...
.330 ctr.
of which not more than 220 ctr. should be due to the
passing load. The constants apply to pieces of
uniform section.
Experiments with spring-steel show that car-
springs should not be loaded to three-fourths of the
small in proportion to the entire deflection. With
a constant strain of 900 ctr. a play of between 900
to 1,200 ctr. is allowed.

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The following exhibit of the results of experi- HOW MERCURIAL THERMOMETERS ARE ducing the subject he said he had often been impressed
ments illustrates the effect of this law of resistance.
With reference to resistance to bending or tension,

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MERCURIAL thermometer is a very simple
instrument. A small glass tube, with a bulb
at one end, containing mercury, and a graduated
scale, constitute all that is essential to it; yet in
160 ctr. this, as in many other cases, simplicity begets diffi-
culty. To make this simple combination perform
its duty accurately is by no means an easy matter.
The first difficulty met with is the want of unifor-
mity in the diameters of the bores of different
tubes, and the varying size of the bore in almost
It is scarcely possible ever to find one
every tube.
the calibre of which is the same throughout its
length, and, if so found, it is the result of pure

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accident. It is obvious, therefore, that unless some means of eliminating the errors which would arise 220 etr. from this source be adopted, nothing like accuracy can be expected in the indications of the instrument. As the character of the bore cannot be altered, the desired result must be obtained in

Of course the greatest fibre-strain actually applied is always less than the absolute breaking limit. The following are presented as immediate results of this law :

Those parts of construction which act positively and negatively, as piston-rods, walking-beams, and the like, must be stronger in the ratio 9:5 than those which are strained in only one direction, as beams, bridges, roof-timbers, &c.

In determining the resistance of bridges and large trusses the weight of the structure, since it forms an absolute constant minimum load, may be left out of account, provided the sum of the effect of proper weight and load does not pass the limits of elasticity.

In the case of car-springs the vibrations are between limits whose difference is quite small compared with the maximun tension; hence the coefficient can be taken larger than in ordinary cases if the steel does not suffer an inch strain of more

another way.

The method employed to obviate this difficulty is called "calibration." Tubes are selected tolerably free from imperfections, and a column of mercury, of one inch or less in length, is introduced into it. The tube is then attached to the frame of a dividing engine, and put in connection with flexible rubber bags, to which pressure is applied, and regulated by screws. The air pressure in one bag being reduced while it is increased in the other, the mercury column may be forced to and held at any part of the

tube.

The mercury being thus brought to the portion of
the tube where the graduation is proposed to com-
mence, the exact position of one end of the column
is marked upon the tube, a microscope with cross
wires being employed to aid the eye of the operator
in performing the operation with exactness. By
means of the rubber bags the mercury is again
forced along until the end of the coluran, where the
first mark is made, is brought under the microscope
cross wise, placed at the other end, and so on
throughout the entire length intended to be gradu-
ated. The varying lengths of the column, which
are recorded, and indicate the variations in the
calibre of the tubes. A permanent mark is made at
the end, as at the beginning of the calibration.
It will be seen, that if the spaces successively
occupied by the mercury be divided into an equal
number of equal parts, any one of these parts will
indicate a corresponding increase of volume, although
the bore of the tube may vary in its diameter.

with the value of the advice tendered in that extract from Montaigne's Essays which prefaces the "Correspondence" columns in the ever-increasingly-valuable ENGLISH MECHANIC, and held it as a matter to be deplored that the correspondents in many cases seemed to entirely overlook it, and hence indulged in funny epistles pregnant with "froth"-not even the creamy, healthy froth which precedes and accompanies the flow of genial, heart-inspiring liquid, but more nearly resembling the vapid effervescence from a sick man's o'er-laboured stomach.

Turning to the subject proper the lecturer began by remarking that the chemistry of the moderns is but the alchemy of the ancients in a further state of developmaterial things into four grand divisions, - Fire, Air, Earth, and Water, chemistry in these days had sub-divided those into upwards of sixty simple bodies, and, what is of more practical importance, had shown how the various elements may be best turned to advantage in the vast workshop of mankind. He then referred at considerable length to the nomenclature

ment. That whereas the ancients had divided all

and notation of chemistry, explaining and illustrating by experiment the difference between mechanical and chemical elements and compounds. During the remainder of the lecture he confined himself solely to the gas oxygen, and by several very interesting and beautiful experiments showed, in a striking manner, its capabilities of supporting combustion.

The lecture was listened to throughout with the most rapt attention, and at the close several questions were put by the members, some of which were answered by Mr. Kemp.

It was announced that at the meeting in September the president would deliver an address on "The Air we Breathe."

Mr. C. E. Gordon was appointed to that post pro tem.
In consequence of the resignation of the secretary,

THE OBSERVING ASTRONOMICAL SOCIETY.
Hon. Sec.-WILLIAM F. DENNING, Ashley-road,
Bristol.

Report of Observations made by the Members during the

is allowable than has been generally applied; but are accurately measured in the different positions, Bedford, reports that the sun's spots observed in July

act.

period from July 7th to August 6th, 1870, inclusive. SOLAR PHENOMENA.-Mr. Thomas G. E. Elger, of

than 800 ctr. It often reaches 900 to 1,000 ctr.;
and with good steel a further increase is possible.
Those parts of boilers which are not exposed to
the fire, if of cylindrical form, are subject to but
slight vibrations, which are caused by the variation
of the tension of the steam. Hence a greater strain
in the parts exposed to the fire, not only the waste
by burning, but also the motion of the molecules
exceeded in number those recorded during the previous
month, but they were, with a few exceptions, small
due to the varying temperature, must be considered.
(less than 30" in diameter), and although pretty equally
distributed between the two hemispheres, those to the
It is not improbable that the continued movement
south of the sun's equator presented a remarkable con-
of molecules, caused by heat, acts to destroy co-
trast both in type and size to those observed to the
hesion, just as vibrations caused by other forces
north of it; the former, as in June, included some
large scattered groups and moderately sized spots of
The effect of strain is entirely different, if it is
the normal class, while the latter consisted chiefly of
constant and static, from the effect when it is
variable and productive of vibrations. It is also
solitary specks, without penumbra, and clusters of mi-
important to consider whether a structure is in
nute black punctures, which frequently assumed very
grotesque configurations. A striking feature of the
tended to serve a purpose for a limited period, or
large groups observed during the early part of the
to stand for an indefinite time. It follows that like
factors of safety do not suit all constructions. In
month was an evident tendency either to close up, or
to become dissociated upon reaching a certain position
every case two factors are necessary; one, which
determines the ratio of absolute breaking strength;
on the disc about half way between the E limb and the
On the 25th one of the largest groups ob-
On the 28th
another, which fixes the ratio to the vibration that ing and boiling points, and no tubes can be used served this year appeared at the E limb.
except such as are found to be approximately perfect. it measured nearly 5' in length, and consisted of a
In the latter case, the arbitrary scale, as marked from large preceding spot 1' 10" in diameter, followed by
the calibration, may be reduced after the determi-a draggling train of "wispy" penumbra, enclosing
This group dwindled away
Another large spot,
very rapidly after the 28th.
nation of the freezing and boiling points into the several small spots.
Fahrenheit scale, by the application of a simple about 50 in diameter, was observed from July 13th
algebraic formula.
Fresh groups observed in the sun's N. hemisphere

induces rupture by indefinite repetition.

The coefficient of safety should be taken large enough in comparison with the absolute breaking strain, that it may compensate for want of homogeneity of material. For this the factor 2 is sufficient. Material requiring a larger coefficient in this respect should be rejected. The limits of elasticity have not thus far been considered, and it must be left to the judgment to determine between single loading, preventing further deflection, can do no harm, if it does not approach the breaking

what limits continuous deflection is allowable. A

* Translated from Polytechnisches Centralblatt.

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