

of t.lio ar.-, uii'l this account* (or the vib 



r j.I.ll 



1UU 



in i 



J 



i which moves tho pendulum is the resolved 

 p.irt. " Imply increases or dooroasos with that foroo, 



-us afford UM a moans of measuring tho foroo 

 .ity and comparing its power at different parts of tho 

 earth. At the equator it is loast, tho diameter there being 

 ., and a part of tho foroo, which is reckoned at t j 

 no by tiio centrifugal foroo produced by the earth's 

 rotation. A pendulum will, therefore, make fewer vibrations 

 ian it will as we move towards tho polo*. Tho times 

 of oscillation vary, then, at different parts of the earth'* 



md, too, that tho time of oscillation depends upon the 

 length of tho pendulum, a longer pendulum making less vibra- 

 in any given time than a short one. Tho rule about this 

 as follows : 



The time of oscillation increases in the same ratio as the square 

 t of the Icmjth t>f the pendulum. 

 If we take three pendulums whose lengths are in the pro- 

 ion of 1,4, and 9 say, for example, 6 inches, 2 feet, and 

 feet 6 inches, respectively we shall find that while the long one 

 .no vibration, that two feet long will mako two, and the 

 shortest, three. In tho latitude of London, a pendulum to beat 

 seconds must have a length of 39*13 inches ; at the equator, the 

 length must only be 39'01 inches. 



In tho compound pendulum all parts must swing at exactly 

 same rate ; but by what we have seen, those nearer the point 

 suspension have a tendency to swing more rapidly, and thus 

 accelerate the motion of those below, while those at the 

 imo end exert just the contrary influence. Now there is 

 idently some point where the particles are as much retarded 

 those below as accelerated by those above, and this point 

 inst move at tho same rate as if it were free. We might, in 

 fact, havo all the weight collected at this spot without altering 

 any degree tho rate of oscillation. 



This point is called the " centre of oscillation," and when 

 speak of a pendulum of any length as e.g., 39'13 inches 

 we measure from this point to that of suspension. This centre 

 of oscillation is always below the centre of gravity. However 

 much wo alter tho weight of the pendulum, provided we mako 

 no difference in the position of this point, the time of oscillation 

 remains exactly the same. Tho rate of vibration, then, is not 

 at all affected by tho nature or weight of tho pendulum, but 

 depends alone upon its length. We see, thus, the way in which 

 we can regulate the speed ; we can either raise the bob by means 

 of a small nut, as is usually done, or we can have a smaller 

 ight sliding on the rod, and raise or lower this. In either 

 i, the effect produced is the same the position of the centre 

 oscillation is moved, and thus the length altered. When the 

 idulum rod is made of metal, as it usually is, it varies in 

 gth with the alterations of temperature, being lengthened by 

 heat and contracted by cold, and thns a source of irregularity 

 is introduced which would be very objectionable. This dif- 

 ficulty is met by what is called the compensation pendulum. 

 In one form of this the bob consists of a cup of mercury. When 

 the rod lengthens by tho heat and lowers the centre of oscilla- 

 tion, the mercury expands and rises, and its bulk ia so arranged 

 that this expansion raises the centre in exactly the same 

 degree as tho expansion of the rod depresses it. In large 

 church clocks the pendulum rod is frequently mado of wood, 

 d thus this difficulty is avoided. 



Another compensating pendulum is composed of parallel bars 

 brass and zinc, so arranged that by their joint alterations in 



;h the position of the bob remains unaltered. 

 The balance wheel of a watch acts on the same principle as 

 )cndulum, its vibrations being isochronous, 

 hen a pendulum is made to swing by itself it soon 

 is to rest; and even if every care bo taken to remove 

 air and rodnco the friction, it will not continue in 

 tion moro than about twenty-four hours. A maintaining 

 ce is therefore needed, when it is employed as a measurer 

 time. This is supplied by the spring or weight of the 

 k. The pendulum rod works in a fork which is attached 

 the anchor and pallets. These catch in the teeth of tho 

 .pement wheel, and allow it at each oscillation to move 

 half a tooth, and then again stop it. The motion 

 the escapement wheel is thus at each stoppage transferred 



to Uia poodolnin, and k*ps it in Tibcatio*. A train of wheel* 

 ojnnooU this esoapeineob with UM hands 



ire now acquired a general afiqnnhitanoo with UM mot* 

 Important fact* of Mechanic*. The snbjet U far from M,- 

 ttaoatod, but wo mint leave 700 to follow it op in book* 

 pooially devoted to it. or in tho page* of "The Technical 

 Educator," tho companion work to thU. Our attention will 

 now be turned to the other branch** of Natural Philosophy, 

 all of which are of groat interest and importance. The ant 

 branch we ahall take up ia HydronUties, which baa b**B 

 claimed by many an a branch of Mechanic*, but U more 

 accurately considered aa a separate scienoa. 



LESSONS IN GERMAN. LI 



} 8.-OENDER OF COMPOUNDS AND FOREIGN WORDS. 



(1.) Compounds in general adopt the gender of their hut 



component ; as : 



Die $offird;e (from $of, court or yard, and Xinfe. church), court 



church. 



Det Jtirttytycf, the churchyard. 

 Dcr <iic$6aum (from tie (Stc^e, the oak, and in Panm. tree), the 



oak tree. 

 Die aBintmtiljlc (from ret ifflint, the wind, and tU TOtyle, mill), 



tho windmill. 

 Dal jRatfytyauj (from m 5iat$, council, and tal jui, house), the* 



council-house. 



(2.) Foreign words, for the most part, when taken into tht 

 German language, retain their original gender. Those, however, 

 that havo become fairly Germanised often take a different gen- 

 der, as they take a different form ; thns, Corpus (the body), 

 which in Latin ia neuter, becomes in German ter Jtorm, which is- 

 masculine. 



. DEB17ATION OF NOU.v 



(1.) To what has been already said ( 2. [3]) concerning tho 

 derivation of nouns, we add here, before entering upon tho sub- 

 joct of Declension, a brief view of the secondary derivatifm, 

 which are made by si^tnificant suffixes. For tho sake of tho 

 learner we subjoin a list of the leading suffixes of this class ; 

 putting in brackets the equivalent English terminations, explain- 

 ing severally their force and use, and illustrating the whole by 

 suitable examples. 



10. SUFFIXES USED IN FORMING NOUNS. 



SUFFIXES. ENGLISH EQlTfALKNTS 



-er [er, ier or yer, sen] 



-ing, or -tin.} [ling, aster'] 



-in [ess, ] 



-ei [y, ry,<jry,<Tj/,ory] 



uno, [ing, urc, ion] 



ftit 



tl-um 



fal 

 -fel 

 -nit! 

 -rficn 



-kin 



XKAxnra. 

 designates (male) persons ; 



also agents or instruments. 

 denotes (often contempt* 



otuly) persons, animal*, and 



designates (female) persons. 

 indicates tho act, practice, or 



place of business. 

 signifies tho act or the eon* 

 to act. 



ttag 



VOUV8. 



( Singer, a singer ( ^ur-jer, a citizen ; doet a sawyer : 

 eso)neim, a tailor ; Hornet, a Roman ; Setrjioer, a resi- 

 dent of Leipzig ; UBiener. a Viennese. 

 V-.urtltv. a i-.iptmn ; ftliMfctlimj. a fugitive; 9h(t|Uaf, % 

 hireling . ticfctnlinj, a poetaster; lnflma, a linnet 

 a hoot or sprig. 



