ZOOLOGT AlTD BOTAJTT, incaOflOOPT, ETC. 709 



Bat an objeetiTe craglit nexer to be taken apart by any one bnt its 

 wuiker. He baa liie IsAe vpon -v^Licli it -wag made, and he aloDe, 

 whea &£ jmHs Imve been separated, can replace tLem in tLeir original 

 •djiKtmeat to die Ofiaenl centre. Any otlter person M-ill be likely to 

 flcxevia iiie eeDseidker too tigbtly or not tigLtly enongb, and will tbus 

 Atov ihe wnlaiMlioms out of tbeir necessarily delicate relations to 

 oae Mwtftw, BeaSden, unless skill and care be exercised in screwing 

 Ae parte togefter, die frcmt and tbe middle combinations will some- 

 loMB be bxcxn^it ni eoniftict, and tbe flint glass, wbicb is Tery tbin at 

 Ae eoite^, will be broheiii Tbe screw-tbread of tbe cells is very 

 iflifafn Yet aoBie pefBcms, after failing to catcb it, apply force 

 OHM^ to bnak iL 



^ A latge aa^e cil-iaaiiica^on lens gets out of order easily. If 

 yon £Bd Ute de£mtioB of ancb objective to 

 ba«e lost iis drnpneaa, jo* may ^ow tbat Fie. 147. 



Ae boat kaa ia oat of eeubm. It bas come in cr" ^zz~izi^ , 

 rtmlmrt widt die iGde. A may alagbt pressure 

 ia aaSeieBt to wedc flie mwririrf. Tbis sns- 

 'eeptSnHty to injury is tmavoidaUe, as every 

 vnH tell yon. It ia ineident to tbe 

 of bigb-angle eonatraction." 



fl fig < i i '« Meebamcal FmgfCT Objective. — 

 1ft. Eu H- Griffitb tbns describes tbis apparatus. 



Tbe eoilax A ''fig. IIT") mores on a fine tbread 

 aad farrw iiiiu n tbe bristle-bolder B. A slit in 

 C hoeps B m poeitioB. On turning A back, tbe 

 apring JJ lifts ihe fiag^r. Tbe jacket to wbicb 

 C asii I) are aitatheii tozoa on liie c^jjeetiTe, so 

 Aat ibe diabam earn, be tanel aa dened. By lifting D tbe finger 

 tarn be TeamamrJL 



The bnade makes a good indicator aleo. 



X^^kHuag-led PriBm instead of a Plane Mirror.* — Mr. G. Hunt, 

 IB rrfrw^Of to Mr. E. M- lielscoi's remark t — " Eigbt-angled prisms 

 " asB waed. ia t dc a eo f c a for the pafpoae of economising every particle 

 " of B^it ; m die llieroseope, bowerer, even witb a 1/2 in. wick, tber© 

 * is moTfe light ibaa one knows wbat to do witb" — points out tbat it is 

 not tbe qaaudkif ot^e li^it {^wbiesb efta easily be controlled;, but tbe 

 quality wkidk •"f*'*— flw foaaa. faeSoBakifi. He believes tbe refected 

 XBja iram dw piaiiiiiii ailveBBd a aria e e aad from tbe front unsilvf^ed 

 •afiaee fneMat Ae h^ak ftoat beiag bfoa^it accurately to focus oa 

 Hut abjoei «■ Ibe aiaflr TUa belief is ficiimded on tbe ibllowiflig 



In tibe iriatrr tiaae, ivbea Ibe kavea are off tbe trees, be placed 

 iLe Micraaespe widi a f^** **^ a^romatic condenser at an opea 

 wiadw iJiyaiim aa old oak, aboat 250 ft. distant. Witb a little 

 Ibe rpfefyj iasa^ of Ibe oak formed at tbe focus of tbe 



waa viewed by a 1/5 objective. Witb suitable apertures 



• Bag. MedL, xli. (1885) p. 414. 

 t See lUt Jonmal, arctc, jj. 338. 

 ber. 2.— Vol. V. 3 A 



