A (scientist says Hint by micro-photpgrapliy it is may to condense a libi ury of 50,000 vc luuios into a box of one Mibic loot capacity. He ha 3 nsnl ]ihnlvgtu[iby fur several yiais iu collecting fcicetific d.it'i end he lus found nol only that this method is chenper than the coil of paper on which to wiite the same amount ol matter, but also tint it occupies only one per cent, of the tiuu required in copying by hand. A special camera ia amployed, having a «uo aud one quarltr inch focus, and lens of one-quarter inch aperture. Suppose that it is defied to copy a table which occupies a page of a technical journal. The paper is laid on ttic desk, and the c.iaiera, wLieh is small and suspended 011 a biacktt above the desk, is focu.-sed to as to in elude the page. A pkte-holder is then put into tim camera and eiposid for ten seconds, it the ilimuir.aliou couits tioin a student lamp ot 32 canidi-pnwer, pbced 011 the desk opposite the papi*, ami oue-ltMilli second i[ Ihoexpusuieis by delight. The plute-hol ler is tl 1111 put away until a coiivei'ieht oppi rluniiy occurs for dc vi loping. i'mui the instant it is difilled to Ci py mi article until tLe time llie o|irr«ti(.u is lioished, it nei-d l ot he mine than 20 seconds. Vt'lxiiKi or 50 plates are eicpwcd, which may hti withiu n ivw k or f.o, thty arc all put iu one tray and dovvb pod lo;;t tl.n'. As i-ll have made U,e same eipoaui:, it is not necessary lo watch thorn carefully, aud in piacliiv they may all he developed, iixid, and lott to wash, 111 ten miii- Cites, The whole linio spent in copying ouo article or table, including preparation for photo graphing, expufciu;, developing, fitting, wash ing, tiliug away, and labelling is less th»u ouo minnle, according to the professot's experience, 'l'iaao netalirts may bo filed away iu small en velopes, stuck to the backs of pasteboard cards. She phtes used arc ouly ouo aud one-quarter inches by one and one-half inches, and can hold upon them 2,0C0 words, bo that each word can be easily real with n small magnifying-glass, This has the advantage of preserving drawings, ritiich show with equal distinctness, and also oi presenting errors in copying,

OLD TORPEDOES.
