THE TAILS OF COMETS.
I.—If we throw a stone into the water, a wave will be produced that will extend in a circle. The size of this wave and the velocity with which it extends depend upon the size of the stone, that is to say, upon the intensity of the mechanical action that created it. The extent and depth of the water are likewise factors.
If we cause a cord to vibrate in the water, we shall obtain a succession of waves, the velocity and size of which will be derived from the cord's size and the intensity of its action. These waves, which are visible upon the surface, constitute what I shall call mechanical waves. But there will be created at the same time other waves, whose velocity of propagation will be much greater than that of the mechanical ones, and apparently independent of mechanical intensity. These are acoustic waves. Finally, there will doubtless be created optical waves, whose velocity will exceed that of the acoustic ones. That is to say, if a person fell into water from a great height, and all his senses were sufficiently acute, he would first perceive a luminous sensation when the first optical wave reached him, then he would perceive the sound produced, and later still he would feel, through a slight tremor, the mechanical wave.[6]
I
Under the action of the same mechanical energy there form, then, in a mass of fluid, waves that vary in nature, intensity, and velocity of propagation; and although but three modes appreciable to our senses have been cited, it does not follow that these are the only ones possible.
We may remark, again, that if we produce a single wave upon water, it will be propagated in a uniform motion, and will form in front of it successive waves whose velocity of propagation is accelerated.
This may explain why sounds perceived at great distances are briefer than at small ones. A detonation that gives a quick dead sound at a few yards is of much longer duration, and softer at a great distance.
The laws that govern the system of wave propagation are, then, very complex.
II
II.—If an obstacle be in the way of the waves, there will occur in each of them an alteration, a break, which it will carry along with it to a greater or less distance. This succession of alterations forms a trace behind the obstacle, and in opposition to the line of the centers. Finally, if the obstacle itself emits waves in space that are of less intensity then those which meet it, these little waves will extend in the wake of the large ones, and will form a trace of parabolic form situated upon the line of the centers.
III
III.—Let us admit, then, that the sun, through the peculiar energy that develops upon its surface or in its atmosphere, engenders in ethereal space successive waves of varying nature and intensity, as has been said above, and let us admit that its mechanical waves are traversed obliquely (Fig. 1) by any spherical body—by a comet, for example; then, under the excitation of the waves that it is traversing, and through its velocity, the comet will itself enter into action, and produce mechanical waves in its turn. As the trace produced in the solar waves consists of an agitation of the ether on such trace, it will become apparent, if we admit that every luminous effect is produced by an excitation—a setting of the ether in vibration. The mechanical waves engender of themselves, then, an emission of optical waves that render perceptible the alteration which they create in each other.
Let a be the position of the comet. The altered wave, a, will carry along the mark of such alteration in the direction a b, while at the same time extending transversely the waves emitted by the comet. During this time the comet will advance to a', and the wave will be altered in its turn, and carry such alteration in the direction, a' b'.
The succession of all these alterations will be found, then, upon a curve a'' d' d, whose first elements, on coming from the comet, will be upon the resultant of the comet's velocity, and of the propagation of the solar waves. Consequently, the slower the motion of the comet, with respect to the velocity of the solar waves, the closer will such resultant approach the line of centers, and the more rectilinear will appear the trace or tail of the comet.
IV
IV.—If the comet have satellites, we shall see, according to the relative position of these, several tails appear, and these will seem to form at different epochs. If c and s be the positions of a comet and a satellite, it will be seen that if, while the comet is proceeding to c', the satellite, through its revolution around it, goes to s', the traces formed at c and s will be extended to d and d', and that we shall have two tails, c' d and s' d', which will be separated at d and d' and seem to be confounded toward c' s'.
V.—When the comet recedes from the sun, the same effect will occur—the tail will precede it, and will be so much the more in a line with the sun in proportion as the velocity of the solar waves exceeds that of the comet.
If we draw a complete diagram (Fig. 4), and admit that the alteration of the solar waves persists indefinitely, we shall see (supposing the phenomenon to begin at a) that when the comet is at a 1, the tail will and be at a 1 b; when it is a 2 the tail will be at a 2 b'; and when it is at a 4, the tail will have become an immense spiral, a 4 b'''. As in reality the trace is extinguished in space, we never see but the origin of it, which is the part of it that is constantly new—that is to say, the part represented in the spirals of Fig. 4.
The comet of 1843 crossed the perihelion with a velocity of 50 leagues per second; it would have only required the velocity of the solar waves' propagation to have been 500 leagues per second to have put the tail in a sensibly direct opposition with the sun.
Knowing the angle γ (Fig. 5) that the tangent to the orbit makes with the sun at a given point, and the angle δ of the track upon such tangent, as well as the velocity v of the comet, we can deduce therefrom the velocity V of the solar waves by the simple expression:
V = v × (sinus δ / sinus(γ - δ)) or (Fig. 1),
V = da/t'',
t'' being the time taken to pass over aa''.
V
VI.—The tail, then, is not a special matter which is transported in space with the comet, but a disturbance in the solar waves, just as sound is an atmospheric disturbance which is propagated with the velocity of the sonorous wave, although the air is not transported. The tail which we see in one position, then, is not that which we see in another; it is constantly renewed. Consequently, it is easy to conceive how, in as brief a time as it took the comet of 1843 to make a half revolution round the sun, the tail which extended to so great a distance appeared to sweep the 180° of space, while at the same time remaining in opposition to the great luminary.
VI
The spiral under consideration may be represented practically. If to a vertical pipe we adapt a horizontal one that revolves with a certain velocity, and throws out water horizontally, it will be understood that, from a bird's eye view, the jet will form a spiral. Each drop of water will recede radially in space, the spiral will keep forming at the jet, and if, through any reason, the latter alone be visible, we shall see a nearly rectilinear jet that will seem to revolve with the pipe.
Finally, if the jet be made to describe a curve, m n (Fig. 4), while it is kept directed toward the opposite of a point, c, the projected water will mark the spiral indicated, and this will continue to widen, and each drop will recede in the direction shown by the arrows.
VII
VII.—It seems to result from this explanation that all the planets and their satellites ought to produce identical effects, and have the appearance of comets. In order to change the conditions, it suffices to admit that the ethereal mass revolves in space around the sun with a velocity which is in each place that of the planets there; and this is very reasonable if, admitting the nebular hypothesis, we draw the deduction that the cause that has communicated the velocity to the successive rings has communicated it to the ethereal mass.
The planets, then, have no appreciable, relative velocity in space, and for this reason do not produce mechanical waves; and, if they become capable of doing so through a peculiar energy developed at their surface, as in the case of the sun, they are still too weak to give very perceptible effects. The satellites, likewise, have relatively too feeble velocities.
The comet, on the contrary, directly penetrates the solar waves, and sometimes has a relatively great velocity in space. If its proper velocity be of directly opposite direction to that of the ethereal mass's rotation, it will then be capable of producing sufficiently intense mechanical effects to affect our vision.
VIII.—Finally, seeing the slight distances at which these stars pass the sun, the attraction upon the comet and its satellites may be very different, and the velocity of rotation of the latter, being added to or deducted from that of the forward motion, there may occur (as in the case shown in Fig. 6) a separation of a satellite from the principal star. The comet then appears to separate into two, and each part follows different routes in space; or, as in Fig. 7, one of the satellites may either fall into the sun or pursue an elliptical orbit and become periodical, while the principal star may preserve a parabolic orbit, and make but one appearance.—A. Goupil.
Certain persons, as well known, undergo an optical impression under the action of certain sounds.
THE DOUBLE ROLE OF THE STING OF THE HONEY BEE.[7]
Very important and highly interesting discoveries have recently been made in regard to a double role played by the sting of the honey bee. These discoveries explain some hitherto inexplicable phenomena in the domestic economy of the ants. It is already known that the honey of our honey bees, when mixed with a tincture of litmus, shows a distinct red color, or, in other words, has an acid reaction. It manifests this peculiarity because of the volatile formic acid which it contains. This admixed acid confers upon crude honey its preservative power. Honey which is purified by treatment with water under heat, or the so-called honey-sirup, spoils sooner, because the formic acid is volatilized. The honey of vicious swarms of bees is characterized by a tart taste and a pungent odor. This effect is produced by the formic acid, which is present in excess in the honey. Hitherto it has been entirely unknown in what way the substratum of this peculiarity of honey, the formic acid in the honey, could enter into this vomit from the honey stomach of the workers. Only the most recent investigations have furnished us an explanation of this process. The sting of the bees is used not only for defense, but quite principally serves the important purpose of contributing to the stored honey an antizymotic and antiseptic substance.
The observation has recently been made that the bees in the hive, even when they are undisturbed, wipe off on the combs the minute drops of bee poison (formic acid) which from time to time exude from the tip of their sting. And this excellent preservative medium is thus sooner or later contributed to the stored honey. The more excitable and the more ready to sting the bees are, the greater will be the quantity of formic acid which is added to the honey, and the admixture of which good honey needs. The praise which is so commonly lavished upon the Ligurian race of our honey bees, which is indisposed to sting—and such praise is still expressed at the peripatetic gatherings of German bee-masters—is therefore from a practical point of view a false praise. Now we understand also why the stingless honey bees of South America collect little honey. It is well known that never more than a very small store of honey is found in felled trees inhabited by stingless Melipona. What should induce the Melipona to accumulate stores which they could not preserve? They lack formic acid. Only three of the eighteen different known species of honey bees of northern Brazil have a sting. A peculiar phenomenon in the life of certain ants has always been problematical, but now it finds also its least forced explanation. It is well known that there are different grain-gathering species of ants. The seeds of grasses and other plants are often preserved for years in their little magazines, without germinating. A very small red ant, which drags grains of wheat and oats into its dwellings, lives in India. These ants are so small that eight or twelve of them have to drag on one grain with the greatest exertion. They travel in two separate ranks over smooth or rough ground, just as it comes, and even up and down steps, at the same regular pace. They have often to travel with their booty more than a thousand meters, to reach their communal storehouse. The renowned investigator Moggridge repeatedly observed that when the ants were prevented from reaching their magazines of grain, the seeds begun to sprout. The same was the case in abandoned magazines of grain. Hence the ants know how to prevent the sprouting of the grains, but the capacity for sprouting is not destroyed. The renowned English investigator John Lubbock, who communicates this and similar facts in his work entitled "Ants, Bees, and Wasps," adds that it is not yet known in what way the ants prevent the sprouting of the collected grains. But now it is demonstrated that here also it is only the formic acid, whose preservative influence goes so far that it can make seed incapable of germination for a determinate time or continuously.
It may be mentioned that we have also among us a species of ant which lives on seeds, and stores these up. This is our Lasius niger, which carries seeds of Viola into its nests, and, as Wittmack has communicated recently to the Sitzungsberichte der gesellschaft naturforschender freunde zu Berlin, does the same with the seeds of Veronica hederaefolia.
Syke states in his account of an Indian ant, Pheidole providens, that this species collects a great store of grass-seeds. But he observed that the ants brought their store of grain into the open air to dry it after the monsoon storms. From this it appears that the preservative effect of the formic acid is destroyed by great moisture, and hence this drying process. So that among the bees the honey which is stored for winter use, and among the ants the stores of grain which serve for food, are preserved by one and the same fluid, formic acid.