T II I. 



338 



THE 



Poiuon show how much this hypothesis may be adroitly 



! of Mewing the pnenomi 



matter is more tru tly inductive, and is similar to that cm- 



.1 in tin- > cf tli<' latent 



in Mr. M .Sir. 



we start from tlif lad tliat forces M >vvcr- 



Inl to prevent the i 



and which pi event tln-ir being turn a.-umlcr without great 



being employed, are yet insensible to bodies ;r 

 minute distances irom them. Here we have ample data 

 lor analytical calculation, the chief difficulty lying in the 

 impr .d calculation relative to definite 



.ntcirrals: nevertheless cnonirh can lie deduced to show 

 li< distribution of a' nd repuls.'. v.ithin 



the \ Tilled bodies. It however requires the 



highest strenclh of analv.-is of a nature somewhat similar 

 to that ein the figure of the earth and 



the t 



Th. >i' the truth of any theory- on this subject is 



that which, with the ; to c\i-t. shall show 



that the locus of the points of lr <, commencing 



fioiu a given point, shall be a plane suiface, or .-. 

 plane surfaces, as exhibited by crystals. 



(Dr. Yin ..;/ l'fnl'i\i,jihij : Various 



Papers in the Mun'urix </r riimtitiit ; and Poissou's Trnitt 

 stir t'.-lrtiiiH CajnUaife.) 



THKOKY, THEORY AND PRA( TICK. If articles 

 upon the mere meaning of words be admissible, it is the 

 quence of the manner in which they are used. Of all 

 the fallacies which infest society, the most common is that 

 of applying to one sense of a word ideas or associations 

 derived from another; and of all the winds in vise. 

 there are few which are mure often subjected to such 

 process than those which stand at the head of this article. 



H\ theory, properly speakimr. is meant the mode of 

 making seen and Known the dependence of truths upon 

 one another: a theory is a connected body of such truths 

 bclongm to one or more common principles. Th- 

 tbis word has enlarged with the boundaries of the sciences. 

 For example, before the discovery of universe] iriavitation. 

 all that was known of any one planet was the empirical 

 formula for one or two of its inequalities. This constituted 

 the theory of the planet 'then so called 1 ) : thus the theory 

 of the moon consisted in t: at of the laws of the 



inequalities called the equation of the centre, the evcc- 

 tion, &c. In our day the point of view is changed ; it is 

 no lontrer the mere exhibition of these inequalities which 

 Mutes the theory, but the deduction of them, a- 

 consequences, limn the principle of (gravitation. The 

 theoretical astronomer now stints from this principle, and. 

 taking only one position and velocity for his inn: 

 data, finds out e\ery inequality of the planetary motions, 

 which were previously known from observation and 

 more, and shows how to form them into tables. The prac- 

 tical a-tn>nomer makes the.-e table*, computes places from 

 them for the current year, compares these places with the 

 results of observation, and returning the comparison into 

 the hands of the theorist, enables him, if Deed be. to cor- 

 rect the original numerical data to which lie applied his 

 methods. The process is now deductive : but before the 

 time of Newton it was the other way. The observer had 

 the t the inequalities were to be collected from 



comparison of observations, and their laws, reduced to their 

 simplest form, were the data for future tables. 



Again, before the introduction of the undulatory hypo- 

 thesis, the 1heoi v of liifht consisted in the exhibition of tin- 

 laws of reflexion and n fraction, with a certain extent of 

 explanation from ti;. iv hypothesis of Newton 



Since that time the ' ""hi has become, thonirh at 



>'ance, a resemblance of the theory of gravitation in 

 its character: prediction has commenced, that is to say. 

 the phenomena which would appear under certain new 

 circumstances have been announced be 

 ments were made to discover them: and CO 

 nounced. Thin is the end to which theory ought to be con- 

 stantly tending ; namely, the discovery of laws of action in 

 so complete a manner that the qucnces of 



thete laws never fail to make their ap| -o that 



i Ti-ry tiling which i- | consequence o! 



IWI when , ,,,.,. ,,f the 



lw is seen in V. 



ll these condition, may be called a perfect theory, or a 

 perfect mathematical theory. 



The next step in the chain of il liicli may 



in most case* be incapable oT attainment. .p' 1 '- 



nothini; i- more certain than that the as-uniptic" 

 particle of matter attracting ev. 



ing to the Newtonian law, lend- to tin 'ion 



-'ial motions, and u;i\< i of 



ion just alluded to. Hut whether U 



does actually take place, or whctb. iiatc 



agent is employed, though it matters nothing <il /'/ 

 to the mathematical (henry, is the next object of in-. 

 Could this point be ascertained, it is mon 

 that the knowledge of the constitution of matter to which 

 it would lend, would open hundreds of import: 

 qucnces even in the application of science to the aits. 

 '' 



; Jlvi-nrii 



re comini; to the distinction between theory and 

 practice, we must observe that theories maybe divided 

 into two classes. the more perfect and the 1. \V. 



cannot say that any theory is absolutely perfect ; but ' 

 are some of which the defects are hardly ] 

 others in which the contrary is t! .the 



theory of th< ml dynamics of :uh- 



rably perfect ; but that of both 

 acted on by molecular forces is in its infancy. \\'e know 



i deal more of the connection of the planetary worlds 

 with each other than we do of the particles which, when 

 connected together, foim a bar of iron or of oak. AVe 

 know that the bar is not perfectly rigid; that it bends and 

 breaks : and the demce of bending which a given force will 

 cause, and the amount of pressure ; duce 



fracture, must be sought for in experiments fiom which, 

 imperfect a.s they are. the laws which would follow Irom 

 a good theory, if we had one, are to be deduced. In such 

 a subject our theory, instead of bcmir an all-sufficient 

 guide, is only a help, the services of which an 

 to an extent which discrimination derived from practi.-e 

 and experience must point out. Many a person who thinks 

 he is proceeding upon experience only, i.s really making 

 a mixture in which there is theory, though his own 

 knowledge of the process he uses, and of it- hisloiy, may 

 not be sufficient to inform him of it. 



A prison who uses an imperfect theory with the con- 

 fidence due only to a jieifcci one, will naturally fall into 

 abundance of mistakes: his predictions will be crossed by 



ling circm. 1 which his theory is not able to 



take tCCOunt, and his credit will be loweied" by the failure. 

 And inasmuch aB more theories an' imperfect than are per- 

 fect, and of those who attend to anything, the n 

 aequii' i judging is small compared with 



that of those who do not get so lar. it must have hap] 

 as it has happened, that a great quantity of inislal, 

 been made by those who do not understand the (me. use of 

 nn imperfect Iheoiy. Hence much dis< 

 brought upon theoiy in general : and the schism of theo- 

 retical and practical men has arisen. Foitunatc 

 many of the former who attend properly to the imp 

 ineni of imperfect theory by piacticc : and many calling 

 themselves piaeticai whosii/.c with avidity all 

 can do for them. :ind who know that st. . 

 has been making her way with giant strides into the tcin- 

 torv of practice for the la.sl centniv and a half. 

 Hy piact:- iiom tin ory . is 



by ns, liut by those who contend for the distinction the 

 a])) lication of that knowledge which comes hum ex 

 pcrience only, and is not sufficient 1;. '1 with any 



general principles to be entitled to the name of a 1: 

 The distinction of labourers in the field of science , 

 into theoretical and piactieal is not strictly a j: 

 there i.s no theorist whose knowledge is all theory; and 

 there is no practical man whose skill is all derived 



icncc. Hut the terms will do well enough to distin- 

 guish (wo classes whose peculiarities it might be difficult 

 to define exactly. 



The practical man. when he i.s really nothing more, i 



who can just do what lie has been taiiL'ht to do. and who 



has acquired skill and judgment in a small range of occu- 



pations. All who pride themselves upon the title would 



be displcasid at tins definition, and we readily admit that 



many of them are entitled to a higher chaiactcr : but only 



e the name by which they deliirht to describe thcm- 



is a wroni; one. They desire, under the name of 



a workman, to claim the qualities of a master. The term 



s, as one of contempt, to designate any- 



