ItYKK. 



1'INAMl' S. 



M 



fir 



with grmi advantage; and that if colonist* could be taught how to 

 extract and oooosntrato tii true colouring principle of these wood*, 

 mob unpco6uble Ubour and expense might be .|nxl Nay, more, 

 UM cwBOSotraUd dy-*Uiff might be profitably imported from places 

 from which the cost of carriage would altogether prevent the importa- 

 tioa of the dyMtuff in ita raw Ute. ThU U matter of great prac- 

 tical importance, and one which has not yet received that attention it 

 Amtrtm. There an no doubt difficulties in the way; but after the 

 many triumph* which man has achieved, we surely noetl not be 

 deUrred by any ordinary difficulties." 



To the above we may add a few valuable observation!, made by Mr. 

 )UwAi in hit ' Commercial Product* of the Vegetable Kingdom,' 

 on the uaeful qualitie* of many simple and well-known plants, and 

 other mibcUixx*. a* dye-material*. " The beauty of the dye* given by 

 i tni'-r' 1 - in the Highland* of Scotland, to some of the clotlw 

 i exhibited [at the Great Exhibition of 1851], should lead 



t* and chemiat* to examine more closely than they have 



hitherto done, the dyo-tufls that might be extracted from British 

 t*. Woad, and the dyers' yellow woad, are both well known. A 

 > of tweed, spun and woven in Ross-shire, was dyed brown and 



__j by such cheap and common dyes as moss and alder-bark ; and 

 th colours were unexceptionable. Sutherland shire tweeds and stock- 

 ing*, possessing a rich brown colour, were produced with no more 

 valuable dye than soot ; in another piece, beautifully dyed, the yellow 

 was obtained from stony rag ; brown from the crops of young heather ; 

 and purple from the same, but subjecting the yarns to a greater action 

 of the dye than was necessary to produce brown. There is very little 

 doubt but that beautiful and permanent dyes, from brown to a very 

 rich purple, might be cheaply produced by scientific preparations of the 

 common heather. The inhabitants of Skye exhibited cloth with a 

 peculiarly rich dye, obtained from the Crobal moss." 



It has been shown in former articles [BLEACHING ; CALICO PRI.NTI.M;] 

 that the legislature has sought to throw a shield of protection around 

 the women and children employed in bleach and print works ; that 

 this attempt succeeded so far as concerned print works; but that 

 bleach work* still remain exempt from the operation of the Factory Acts. 

 We have now to add that dye works are in the same category as bleach 

 works. In the years 1854-5-6-7. both classes of establishments were 

 subject to many parliamentary discussions, and to inquiries by com- 

 missionersending by a postponement of all legislation thereon. 



DYKE. A structure of earth, or of masonry, for the purpose of 

 resisting the inroads of the sea, or of any large body of water ; or for 

 the purpose of guiding and controlling the action of the floods of rivers, 

 or of preventing the tidal action of rivers, or of arms of the sea, from 

 exercising itself in a way which might be injurious to the surrounding 

 lauds. The construction and form of dykes must evidently depend 

 to a great extent upon the position in which they are placed, and upon 

 the nature of the materials of which they are to be composed ; and 

 the principles to be followed in designing them must equally depend 

 upon the local conditions they will have to fulfil It will therefore 

 be preferable to treat the whole subject of river or fen-dykes under 

 the head of RIVER IMPROVEMENTS; and that of sea-dykes under the 

 head of SEA DEFENCES. 



DYNAM. In estimating the effect of mechanical labour, it is 

 desirable to have some idea of a simple unit well fixed in the mind. All 

 who have studied the subject know the advantage there is in referring 

 every kind of pressure to weight, and measuring it by the weight 

 which will balance it. Thus if one hundred pounds weight will bend 

 a spring into a certain position, we have no difficulty in substituting 

 an opposite force to the weight for the recoil of the spring at the point 

 of application. It is equally convenient to arrive at a distinct notion 

 of a unit of useful effect in the workmanship of machines ; but it may 

 not at first be so apparent that the thing is practicable. Nevertheless, 

 the theory of dynamics contains the means of showing that all the effects 

 of a given power are convertible in the following manner. Exclude 

 friction and useless resistances, and suppose that a steam-engine, for 

 instance, will exhaust a certain quantity of fuel in raising a ton 

 through a hundred feet, no power being thrown away. Suppose also 

 that tee same machine, with the same fuel, will completely expend the 

 power of that fuel in drawing a certain iron cylinder into wire of a 

 thousand times its length. Then, if a machine could be constructed 

 which arts by the descent of a weight, and draws wire without any loss 

 of power, the descent of a ton through a hundred feet would just be 

 sufficient moving power to draw out the cylinder just mentioned to a 

 thousand times its length. We do not of course mean to say that such 

 freedom from loss of power exists. If, for example, a certain quantity 

 of fuel were made to raise water by a steam-engine, and the water so 

 raised wen allowed to fall upon a wheel and grind corn, it is certain 

 that the water would not grind so much corn as the steam-engine 

 itself directly applied to that purpose. But this arises from useless 

 increase of resistances, and from badness of adaptation : it is impossible 

 to make all the water in a fall produce its utmost effect upon a wheel. 

 But what we say is, that were it possible to make adaptation perfect, 

 there exist* in the water raised exactly the same capability of grinding 

 corn that there in in the fuel which raised the water. 



This being the case, we may consider any machine as simply applied 

 to raising a weight, and look upon the weight raised as a dynamical 

 synonym for any possible effect that the machine could have produced. 



And the theory further teaches u* that the useful effect of any appli- 

 cation of power varies jointly as the weight raised, and the height to 

 which it is raised. Thus twice as much power must be cxpen> 

 raise a double weight to the same height, or the same weight to a 

 double height Accordingly, the product of the number of pounds 

 raised, and the number of feet to which it is raised, is a > 

 measure of the quantity of power. For example, a certain expenditun- 

 of force raises 70 pounds through 20 feet ; what comparative expendi- 

 ture will raise 120 pounds through 210 feet f The product 70 x 20 or 

 1400 is to the product 120 x 210 or 25,200 in the proportion of 1 to 18 ; 

 accordingly, the second work requires 18 times the power of the fin-t. 

 Whether it shall be done by 18 engines, or by an application of 18 

 time* as much power to one engine, is merely a question of adaptation. 



We can convert the above relative measurement into an absolute 

 form by M'"p'"g as a unit one pound raised through one foot ; It t 

 this be called a di/iutm, or dynamical unit. Thus in the first job above 

 mentioned, there are 1400 dynams of work to do. Whether it be con- 

 sidered as 1400 pounds raised through one foot, or one pound through 

 1400 feet, or 100 pounds raised through 14 feet, 4c. Ac., matters 

 nothing : it is 1400 times as much work as one pound raised through 

 one foot Thus, what is commonly called a hone-power is meant by 

 our engineers to signify 550 dynams in a second; a steam-engine 

 which can raise one pound through 550 feet in every second is said to 

 be of one-hone pouter. 



This term was introduced by French writers, who called th.- 

 of a cubic metre of water nosed through one metre, a dynu 

 (It/name. Dr. Wbewell (' Mechanics of Engineering,' 8vo, p. 150, 

 Cambridge, 1841,) proposed to naturalise the term dynam as applied to 

 our most convenient units, the pound and the foot. 



It U for want of a distinct notion of this kind that many persons fall 

 into the error about force and its effects, which lead them to contrive 

 perpetual motions. But independently of this, there is a great practical 

 utility in having a specific name for a quantity of work done, m.l.- 

 pendently of all incidental circumstances ; for something which should 

 allow us a proper expression for the result of a quantity of fuel or 

 other generator of force without the necessity of describing a particular 

 mode of using the force. Watt was really the first who assumed, as a 

 dynamic unit, the simple notion of one pound raised one foot ; but he 

 did not venture on a name, though the now common term, the duly <>f 

 an engine, first used by him, has reference to the number of such 

 simple units as may be obtained from the engine.* The late Davies 

 Gilbert, in his paper ' On the expediency of assigning specific names to 

 all such functions of simple elements as represent definite physical 

 properties ' (Phil. Trans., 1827), proposed to represent the product of 

 the pounds raised and the feet through which they are raised by tin- 

 term efficiency. But he did not go further, and assign a name to the 

 unit of efficiency. This simple step, which is of more importance in 

 the propagation of clear ideas than many persons will think it to be, is 

 due to the French writers. 



1 1 V X AMETEK. [MICROMETER.] 



DYNA'MICS (Svyofut, force), a word of comparatively modern use, 

 now universally adopted as signifying the science of matter in motion. 

 as distinguished from ttatici, which relates to matter at rest. : 

 so general a term, our plan requires us simply to refer the reader to 

 the several articles connected with the subject 



Dynamics may be divided into two distinct parts : the mathematical 

 consideration of motion, without reference to any connection with its 

 cause ; and the experimental investigation of the connection between 

 pressure and the motion produced by it, together with the mathematical 

 exhibition of the laws under which the second is a consequence of the 

 first But for the purposes of classification, dynamics is better sub- 

 divided into (1) dynamics of a particle, and (2) dynamics of a ;//' 

 body. When the moving matter is considered as condensed into a 

 single particle, the laws of its motion may bo very accurately and 

 conveniently traced under the following heads : 



(1.) The laws of motion absolute and relath <. 



(2.) Collision and impact, of moving particles. 



(3.) Motion down inclined plane*. 



(4.) Motion under the action of central forces. 



(5.) Curvilinear motion, as of projectiles. 



(6.) Motion in resisting media. 



(7.) Constrained motion, or motion of a particle along curved tubes, 

 wires, &c. 



But if the body be necessarily of some magnitude, and if it be rigid, 

 that in, if its component particles, or its component parts (if it be a 

 system), be supposed to bear, throughout the action, the same in- 

 variable position with respect to one another, then we have the 

 following subdivisions of the dynamics of a riyid body : 



(1.) Motion about a fixed axis, as of pendulums. 



(2.) Motion about a fixed point 



(8.) Motion of a free rigid body. 



(4.) Motion of a rigid system. 



(5.) Motion under the action of impulsive or instantaneous forces. 



By referring therefore to such articles as COLLISION ; MOTION ; 



Or rather, according to ^Watt's icw, the pmcer U the quantity of work 

 which an engine can perform In a given time ; the duly is the quantity which 

 it can perform by a given expenditure of fuel. 



