On the Luminousness of the Ocean.

The luminousness of the ocean is one of the most beautiful phenomena of nature, which excites surprise, although, for months together, it may be seen every night.

The sea is phosphorescent in all latitudes; but he who has not witnessed this phenomenon in the torrid zone, and especially in the Pacific Ocean, can form but an imperfect idea of the magnificence of such a spectacle.

When a vessel of war, impelled by a fresh breeze, cleaves the foamy waves, and one is stationed near the shrouds, he cannot be satisfied with viewing the beautiful phenomenon which presents itself.

Every time that the side of the ship, as she rolls, emerges from the water, flashes of reddish light seem to issue from the keel, and dart toward the surface of the sea.

Le Gentil and the elder Forster , explained the appearance of these flashes by the electrical friction of the water against the body of the advancing ship.

But in the present state of our knowledge, this explanation is no longer admissible.

Voyage aux Indes, t. i. p. 685‒698.

Observations made during a voyage round the world, 1683, p. 57.

In German.

There are few points of natural history respecting which there have been so many disputes as the light emitted by the waters of the ocean.

What we know with precision on the subject, reduces itself to the following facts.

There are various shining mollusca which, during their life, emit at pleasure a rather weak phosphoric light, generally of a bluish colour.

This is observed in the Nereis noctiluca, the Medusa pelagica, var. β, and the Monephora noctiluca, discovered during Captain Baudin’s expedition . Of this number are also the microscopic animals, which have not as yet been determined, and which Forster saw swimming in the sea in innumerable multitudes, near the Cape of Good Hope.

The luminousness of sea water is sometimes occasioned by these living lanterns.

I say sometimes; for, in most cases, notwithstanding the use of magnifying glasses, no animal is perceived in luminous water; and yet, whenever the wave happens to strike a hard body and breaks, producing foam, and whenever the water is strongly agitated, a light is produced resembling a flash of lightning.

This phenomenon probably originates from the decomposed fibrils of dead mollusca which exist in infinite quantity in the depths of the sea.

When this luminous water is passed through a piece of dense cloth, these fibrils are sometimes detached from it under the form of luminous points.

When we bathed in the evening in the Gulf of Cariaco, near Cumana, some parts of our bodies remained luminous on coming out of the water.

The luminous fibres stuck to the skin.

From the immense quantity of mollusca dispersed through all the seas of the torrid zone, it need not be surprising that the water of the sea is luminous, even when no organic matter can be separated from it.

The infinite division of all the dead bodies of dagyses and medusæ may render the entire sea capable of being considered as a gelatinous fluid, and which is in consequence luminous, has a nauseous taste, cannot be drunk by man, but affords nourishment to many fishes.

If a board be rubbed with a part of the body of the Medusa hysocella, the place rubbed becomes luminous whenever the finger, well dried, is passed over it.

During my passage to South America, I sometimes put a medusa on a tin plate.

If I struck the plate with another metal, the smallest vibrations of the tin were sufficient to make the animal shine.

How did the blow and the vibration act in this case?

Was the temperature instantaneously raised?

Were new surfaces uncovered, or did the blow make the phosphuretted hydrogen gas escape, so that, coming into contact with the oxygen of the atmosphere, or with the water of the sea, it produced combustion?

This effect of the blow which excites the light is particularly striking in a jumbling sea, when the waves dash against each other in all directions.

Between the tropics, I have seen the sea luminous at all temperatures; but it was more so before storms, or when the sky was lowering, cloudy, and much overcast.

Cold and heat seem to have little influence upon this phenomenon; for, on the Bank of Newfoundland, the phosphorescence is often very strong at the severest time of the winter.

Sometimes, all other circumstances appearing to be the same, the phosphorescence is very distinct on one night, and the following night there is scarcely any.

Does the atmosphere favour this disengagement of light, this combustion of phosphuretted hydrogen?

Or do not these differences depend merely upon chance, which leads the navigator into a sea more or less filled with mollusca?

Perhaps, also, the luminous animals only come to the surface of the sea when the atmosphere is in a certain state. M.

Bory St. Vincent, asks with reason, why our fresh marsh-water, which is filled with polypi, is not luminous?

It would appear in fact, that a particular mixture of organic particles is necessary to favour this disengagement of light.

Willow-wood is more phosphorescent than oak.

In England, salt-water has been rendered luminous by casting herring brine into it.

Galvanic experiments shew that the luminous state of living animals depends upon an irritation of the nerves.

I have seen an Elater noctilucus, which died, diffuse a strong glow when I touched its anterior extremities with tin or silver.

Sometimes, also, the medusæ give out a stronger light at the moment when the galvanic chain is closed.

Humboldt, Tableaux de la Nature, tom. ii. p. 80‒87.

Forskoe, Fauna Ægyptiaco-Arabica, p. 109.

Bory St Vincent, Voyage aux Iles d’Afrique, t. i. p. 107, pl. 6.

The genus Dagysa belongs to the Salpa tribe of Cuvier.