Page:Encyclopædia Britannica, Ninth Edition, v. 7.djvu/189

Rh double their size. In some phases of this process the gela tinous sac bears a considerable resemblance to that lowest form of animal life known by the name of Amoeba, so much so that an inexperienced observer might suppose that the object before him was an Amoeba gorged with diatomaceous frustules.

Mode of Preparation.—The Diatomacese are usually gathered in small bottles, and special care should be taken to collect them as free as possible from extraneous matter. A small portion having been examined under the microscope, should the gathering be thought worthy of preservation, some of the material is boiled in acid for the purpose of cleaning it. The acids usually employed are hydrochloric, nitric, or sulphuric, according as circumstances require. When the operator considers that by this process all foreign matter has been eliminated, the residuum is put into a pre cipitating jar of a conical shape, broader at the bottom than at the top, and covered to the brim with filtered or distilled water. When the diatoms have settled in the bottom of the jar, the supernatant fluid is carefully removed by a syringe or some similar instrument, so that the sediment be not disturbed. The jar is again filled with water, and the process repeated till the acid has been completely removed. It is desirable afterwards to boil the sediment for a short time with supercarbonate of soda, the alkali being removed in the same manner as the acid. A small portion may then be placed with a pipette upon a slip of glass, and, when the moisture has been thoroughly evaporated, the film that remains should be covered with dilute Canada balsam, and, a thia glass cover having been gently laid over the balsam, the preparation should be laid aside for a short time to harden, and then is ready for observation.

General Remarks.—Like all other organisms, the Diatomacese doubtless have a definite function assigned to them in the grand system of creation, but a special interest attaches to them. Allusion has been made to the fact that the soft cell of these organisms is encased in a siliceous epiderm. When the plant has fulfilled its natural course the siliceous covering sinks to the bottom of the water in which it had lived, and there forms part of the sediment. When in the process of ages, as it has often happened, the accumulated sediment has been hardened into solid rock, the siliceous exuviae of the diatoms remain unaltered, and, if the rock be disintegrated by natural or artificial means, may be removed from what has been called &quot; their stony shroud,&quot; and subjected to examination under the microscope. The forms found may from their character help in some degree to illustrate the conditions under which the stratum of rock had been originally deposited. Vast deposits of Diatomacete have been discovered in various parts of the world, some the deposit of fresh, others of salt water. Of these deposits the most remark able for extent, as well as for the number and beauty of the species contained in it, is that of llichmond, in Virginia, one of the United States of America. It is said to extend for many miles, and to be in some places at last 40 feet deep. The material has long been used as a polishing powder, and recently has been largely employed in the manufacture of the powerful explosive agent known as dynamite. It is a remarkable fact that existing species of Diatomaceae have been traced so far down as the lower strata of the Tertiary formation ; and, though the genera tions of a diatom in the space of a few months far exceed in number the generation of man during the period usually assigned to the existence of the race, the fossil genera and species are in all respects to the most minute details identical with the numerous living representatives of their class.  DIAZ DE LA PEÑA, (1809-1876), a French artist, distinguished chiefly as a landscape painter, was born at Bordeaux in August 1 809. His first works were exhibited at the Salon in 1831, and attracted little notice, being poor in colour, the quality for which he after wards became conspicuous. The same criticism applies to the pictures he exhibited annually until 1840, when his style underwent a decided change. His Nymphes do Calypso (1840), Le Reve (1841), Vue de Bas-Bre&quot;au, L Orientale, Le Mal^fice, and Les Bohe miens se rendant a une Fete (1844), showed in an increasing degree the rich ness of colour and the mastery of the more subtle effects of light and. hade which ultimately obtained for Diaz a place in the first rank of landscape painters. His powers were seen at their best in his Baigneuse and L Amour de sarmo (1851), and in the pictures he sent to the Paris Exhibition of 1855, Les Presents d Amour, La Rivale, La Fin d un Beau Jour, Nymphe Endormie, Les Dernieres Larmes, &c. As the titles of several of these works indicate, Diaz endeavoured to add to the interest of his landscapes by introducing into them the personages of the classical mythology. Late in his career he devoted himself to genre subjects with but indifferent success. Diaz received a medal of the third class in 1844, of the second class in 1846, and of the first class in 1848 ; and in 1851 he was made a chevalier of the Legion of Honour. He died in November 1876.  DIBDIN, (1745-1814), a well-known writer of songs and musical composer, was born at Southampton on the 15th March 1745, and was the youngest of a family of eighteen. His parents designing him for the church, he was sent to Winchester ; but his love of music early diverted his thoughts from the clerical profession. After receiving some instruction from Kent, the organist of Winchester Cathedral, he went to London at the age of fifteen. In the following year his first work, an operetta entitled The /Shepherd s Artifice, with words and music by himself, was produced at Covent Garden Theatre. This proved successful, and was followed by other works, his reputation being firmly established by the music to the play of The Padlock, which was produced at Drury Lane under Garrick s management in 1768, the composer himself taking the part of Mungo. He continued for some years to be connected with Drury Lane, both as composer and as actor, and produced during this period two of his best known works, The Waterman (1774) and The Quaker (1775). A quarrel with Garrick led to the termination of his engagement, and in 1782 he became joint manager of the lloyal Circus, afterwards known as the Surrey Theatre. In three years he lost this position owing to a quarrel with his partner. In 1788 he sailed for the East Indies on the invitation of a sailor brother (the &quot; Tom Bowling &quot; of his famous song) ; but, the vessel having put in to Torbay in stress of weather, he changed his mind and returned to London. A series of mono-dramatic entertain ments which he gave at his theatre, Sans Souci, in Leicester Square, brought his songs, music, and recitations more prominently into notice, and permanently established his fame as a lyric poet. It was at these entertainments that he first introduced many of those sea songs which so powerfully influenced the national spirit. The words breathed the simple loyalty and dauntless courage that are the cardinal virtues of the British sailor, and the music was appropriate and naturally melodious. Their effect in stimulating and ennobling the spirit of the navy during the war with France was so marked as to call for special acknowledgment. On retiring from public life, in 1805, Dibdin was rewarded by Government with a pension of 200 a year, of which he was only for a time deprived under the administration of Lord Grenville. Dibdin died of paralysis in 1814. Besides his Musical Tour through England (1788), his Professional Life,m autobiography 