162 



DYER- DYSART. 



they possess but little fixity when thus formed, ilicy 

 are denominated the fugitive colours. 1. AW is made 

 1'rora Brazil wood and peach wood. 2. Black. A 

 strong extract of galls and deuto-nitrate of iron. 3. 

 Purple. Extract of logwood and the deiito-nitrate of 

 iron. 4. Yellow. Extract of quercitron bark, or 

 French berries, and nitro-muriate of tin. 5. Blue. 

 Prussian blue and solution of tin. Fugitive colours 

 are thickened with gum tragacanth, and are some- 

 times sent to market without being washed. 



DYER, JOHN, an agreeable poet, of the secondary 

 class was born at Aberglasney, in Caermarthenshire, 

 in 1700, and educated at Westminster school. Being 

 left, by the death of his father, at liberty to follow 

 liis own inclination, he became a pupil to Richard- 

 MIII, the painter, and travelled through Wales as an 

 itinerant artist, but never seems to have gained any 

 distinction in that capacity. In 1727, he made him- 

 self known as a poet, by the publication of his cele- 

 brated Grongar Hill. The intermixture of moral re- 

 flections, introduced in an easy manner, with the de- 

 scription of rural scenery, has rendered this poem 

 highly and deservedly popular. After the publication 

 of Grongar Hill, he went to Rome for professional 

 improvement, and published, in 1740, a poem in blank 

 verse, under the title of the Ruins of Rome. Not 

 appearing likely to succeed in his profession, he was 

 i-ecommended to take orders, and was accordingly or- 

 dained by doctor Thomas, bishop of Lincoln. He then 

 married, and retired to a small living in Leicester- 

 shire, which he soon afterwards exclianged for another 

 in Lincolnshire, to which a second was subsequently 

 added. In 1757, he published his largest poem, 

 the Fleece, in five books, a very ingenious produc- 

 tion. He died in 1758. His poems, which comprise 

 u few more pieces than those already mentioned, 

 were published in 1 vol. 8vo. 1761. 



DYKE. See Dike. 



DYKE, VAN. See Vandyke. 



D YNAMETER, measurer of increase, avgometre ; 

 an instrument for measuring the magnifying power 

 of telescopes. It consists of a small tube, with a 

 transparent plate, exactly divided, which is fixed to 

 the tube of a telescope, in order to measure exactly 

 the diameter of the distinct image of the eye-glass. 



DYNAMICS is the science of moving powers, or 

 of the action of forces on solid bodies, when the re- 

 sult of that action is motion. Mechanics, in its 

 anost extensive meaning, is the science which treats 

 of quantity, of extension, and of motion. Now, that 

 branch of it which considers the state of solids at rest, 

 such as their equilibrium, their weight, pressure, &c. , 

 is called statics ; and that which treats of their mo- 

 tion, dynamics. So when fluids instead of solids, are 

 the subjects of investigation, that branch which treats 

 of their equilibrium, pressure, &c., is called hydro- 

 statics, and that which treats of their motion, hydro- 

 dynamics. 



DYNAMIC AND ATOMIC THEORIES; the 

 names given to two celebrated systems, explanatory 

 of the essential constitution of matter. In the dy- 

 namic theory, every body is considered as a space 

 filled with continuous matter ; porosity then becomes 

 an accidental quality, but compressibility and dilata- 

 bility essential properties. The state of a body de- 

 pends entirely on certain attracting and repelling 

 forces ; and its volumes must change with every 

 change hi the relative proportions of these forces. 

 All the varieties of matter are explained by suppos- 

 ing the existence of certain primitive simple substan- 

 ces, the different combinations of which produce all 

 bodies. When two substances combine chemically, 

 they must be considered, on this system, to penetrate 

 each other mutually. The partisans of the atomic 

 theory suppose every body to be composed of indi- 



viMhle. and impenetrable particles, which tlicy term 

 dtutins. These are almost infinitely smaJl, with void 

 spaces between them, so that this tlicory makes 

 porosity essential to matter. The atoms are not in 

 contact, but are kept in their relative positions, at 

 certain distances, by certain attractive and repulsive 

 forces ; from whence it arises, that, in the volume of 

 each body, there is much more void space than mat- 

 ter. On this system, the diversities in bodies may l>e 

 explained either by an essential difference in the 

 atoms themselves, or by a difference in their form, 

 size, position, and distance. When two substances 

 combine chemically, the atoms of one penetrate 

 the interstices of the other, and the atoms of the two 

 combine so intimately, tliat they become, in a manner, 

 new sorts of constituent particles, excepting they are 

 not simple, but compound. 



DYNAMOMETER. Instruments for measuring 

 the relative strength of men, and animals, as also the 

 force of machinery are so called. 



O 



The accompanying cut represents a very simple 

 Dynamometer, for measuring the force of machinery, 

 A E B is a lever made of steel, having two spreading 

 branches D A, D B capable of being fixed on the 

 circumference of a pulley by means of the pinching 

 screws A and B. This pulley is firmly fixed on the 

 end of the shaft C, so as to revolve with it. The 

 pulley revolving in the direction A B, would carry 

 the lever round with it, and the end E would revolve 

 also, but it is checked by the pin F fixed in the wall. 

 But there is a scale G attached to the end E of the 

 lever, into which weights are put in order to weigh 

 down the lever so that it will not rise to the pin F. 

 When the pulley continues to revolve, and has power 

 sufficient to keep the lever nearly touching the pin 

 F, then the weights in the scale will indicate the 

 mechanical effect of the shaft. Care however should 

 be taken not to add more weights to the scale G, 

 than are just sufficient to keep Uie lever clear of the 

 pin, for if more be added the effective leverage will 

 be shortened. 



DYSART, a royal burgh in the county of Fife, si- 

 tuated on the Frith of Forth, 14 miles N. E. of 

 Edinburgh. It has a good harbour, formerly defended 

 by a battery, called the Fort, constructed by Oliver 

 Cromwell, on the summit of a high rock. To this 

 port belong about forty sail of shipping, employed 

 in the exportation of coal and iron from the rich 

 mines in the vicinity, also of vast quantities of sea- 

 salt manufactured here, and in the importation o? 

 foreign produce, which has much increased since 

 1756. A number of the inhabitants likewise find 

 employment in the iron-works, ship-building, in an 

 extensive manufacture of linen, particularly checks. 

 The town, said to occupy the site of a Roman sta- 

 tion is pleasantly seated on a gentle acclivity, rising 

 from the south or margin of the Frith, and consists ol 

 three principal streets, diverging from the market- 

 place in the centre, and crossed by several inferior 

 ones ; its marKets are well supplied, though it L- 



