THE SCREW. COMPARATIVE VALUE OF FODDER. 



36-3 



M 



same maimer as ike propornon of the pofrer to 

 the -weisht in the wheei and axle. 



We have hitherto considered the scrsrvc as an 

 ensine used to overcome sreat resistances- It 

 is also eminentiy t:=e!"! in ?>^v^-2l r^cp^rr—^cts 

 oicxperimenii. - - 

 very minate r_ - 



of which CO old - - _ 



other means. The verj Siuw n^otiou wiuca sulv 

 be irapaned to the end of a screw, by a very 

 coesidenible inorion in the power, renders it 

 pecoiiariy well aiipied for this purpose. To 

 explain the maii-:er in ■^T::?h :: :? cppl-?^ — ?^?" 

 pose a scrv^v to be s- - 



in an inch, each reTc 



Tsnce its point thrt^.-- : : ;. ; i. 



inch. Now. suppose tiie ut^d oi tae screw to be 

 a circle, wliose diameter is an inch, the cinram- 

 ference of the head will be so-.--'-^ r — -e 

 than three inches : this may be - 

 into 8 hundred equal parts disdn^ . 

 a fixed hsdex be presented to this ^^i.i:.;ed 

 circumference, the bandreuth part of a revolu- 

 don oi the scrsw may be observed, fay nc-ria^ 

 the passase of one division of the head ander 

 the index. Since one entire revolation ot the 

 head moves the pern: tlir.?urh the fiftieth of an 

 inch, one division v.ill ^o.Tesrcr.d to the Sve 

 thoasandth ot an in-:h.. In order to observe the 

 jQodcKi of the point of the screw in this case, a 

 fine wire is atticLed to iu «"rach is carried 

 across the field of vie-w oi a power*^ micro- 

 scope, by which the modon is so tnasnmed as to 

 be disrinctly perceptible, 



A screw nsed lor sach ptirposes is called a 

 micrometer scmr. Such an apparatus is nsa- 

 ally attached to the licubs of sradoated instra- 

 menis. tor the p':trpoie ci astronomical and odter 

 observation. Wi± -ii: the aid of this apparatns, 

 ao observation cooid be taken with srealer ae- 

 cnracy than the anicwmt of the anallest diviaon 

 tipon the limb. Thusi. if an instroment fi>r mea- 

 soring a3?ies were ilivided into small arches of 

 one mtnate, and an angle were observed which 

 bro'iL-b: the index of tl>e instrument to some 

 ween rwo divisions, we coald onhr 

 •.hat the observed angle Biost cmast 

 . . --. number of degrees and minntes. to- 

 . r ■• • -n additional number of seconds. 

 f,: i"? unknown, inasmuch as there 

 - - -•' ascertaining the tiractiaB 

 he index and the adjacent 

 . T.-. Bat if a screw be 

 pruviieh. -hv 'n tcoves throasfa a 



space e»:'ial t . ot the instrtunent. 



with sixty rev; - head, and the bead 



itseb' be divided mio uae hondred equal parts. 

 each complete nerolution of the screw will cor- 

 respond to the -■"-•" •"- ---'. of a minate. or to 

 one second, ai. - n on the bead of d»e 



screw will corr-. - e hondredih part of 



& second. The In :• x >-^g attached to this 

 screw, let the bead be mmed until the index be 

 ntoved fi-om its obiserved poisition to the adjacent 

 divisiou of the ilmb. The number of compile 

 rerolutioas of the screw necessary to aocomplisfa 

 this will be the camber of seconds : and die 

 nomber of paKs of a revolution over tbe com- 

 plete r."T:"b<'r '""f r°v--'iT:'.i-?T^s \^'il! Iv die han- 

 drt 1 ' e added 



U.. •. Slaved. 



I: - . - 'tments 



that th.e ui.^r,>Ui<;ur s^.-t-- e; any 



spares whatever city be n h. An 



instance oi its mechanicai -. - K? 



oaeationed in a steel-yard, ; ^s- 



!e. .,.. X . V . 

 this weish: c 



■ oy a given 



ted arm of a 



- --- l:-h 



Hunters screw, alresdv described, seems to 



! b- 



COKPARATITF VaLLE OF DiFFEKEyT KtypS 



OF FoDDFS. — The foUowiEg table is the resalt 



of experiments made by the pritjcipal agricnl- 



tnrisis of the contiiient. and ptibli^ied by il. 

 Antoine at Xancy. The best tipland mesdo^sr 



hay is taken as tbe standard, at 100 Fbs. : and tbe 

 specified weisbt of the other kinds of fodder 

 enttmeratcd are reqaired to prodtice the same 

 resolts : 



GoodlsT foi 100 



A£enziatfa hay 102 



Ctover hsy. made wboi the Kcssom is 



ccBEipJeteJT devdcmed » 



IMaov bejbre die bloestHn espsnds S@ 



Ooresr, second crop ^^ 



Leceraehar -'. 9? 



Saniiwn bay 3 



Tire bay--"- ?1 



Sper^Oia arrears, dried .30 



OoTiO' hay. ^er die seed 14o 



Gieen I]idi2neam iTo 



Vetcises or Hies, grerai 41) 



Green clorer 4.5T 



Green spatula i^ 



Stransatdieaiesof Jerosalonanichoices 3S5 



Cow-c^bin^ leaves. 541 



Beet-^oot Ian«3. "iX) 



PoCKofaaolm 3T0 



Syesoraw- 442 



OatEDsw. li« 



PMshanha. 153 



Tettfa kaabtt l.igi 



BcsB haahn. 140 



BnckiHiea* stnw 195 



Dried saiks of Jerasalem anicbolses. l':0 



Dried staOs of bidisn ram 4^30 



Mi:>i straw 230 



Raw poeaioes 301 



&xled dizxOh. . 1T5 



>Vbi» ^lesias beet es) 



MmaaA-wunei rrs> 



Tnrupe i:4 



CaiTots 575 



S-»re«iish Tcrcips ' Sjl8 



Dina. with ieaTies OQ 350 



Gnin — ^Rve 54 



WTsea 42 



Bariey 51 



Oass.... a» 



Vetdies jO 



PWBL 45 



Beaosi. 45 



Bockwbeat. 64 



bdiiBeanL f ' 57 



iJBseedcake (S9 



Wketttna 1C6 



Rye taaa. 109 



WbMc peas aad oat ^taST- ler 



R^ and bariej <^a£ K9 



