HAVING worked with the microscope more than thirty years for medical and scientific purposes,-following the graclual porfectiiig of the instrument-I was anxious to examine the power of Ainericnii microscopes. But my occupation in the Museum and ignorancc of the English language have prevented the accoiiiplisliiiieiit of niy wishes. I ordered a new microscope of M. Hart1idi in Paris, which was kindly formarded to nie by $1. Nilne-Eclwnrcls. Tlic Frciich instriiments arc noted throughout Europe

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... r tlicir powcr aid finish, and in ordcr to ,judge impirtially, I aliose one of thcse, ratlier than a Gerninii instrunleiit. It is well known that marly every nation claims for itself the liighcst dcgrec of pdcctiou iii the manufacture of microscopes. No Englishman moult1 aeliiiowledge the superiority of a French instrument, nor a Prciicliniaii tliat of an English instrument. I n Qerinaiiy alone, l'russimi, Austrian, Saxon, and Bavarian iiianuhcturers all claim prc-ciiiinence for their rcspectivc instninleuts, iiot only coinpml with cach other, but with those of American a i d English nirmmif;icturc. Tliero has been no unaniniity of opinion aiiiong scicntific incii in r~p d to this question. I tliink tliese co~iflict~iiig claims arc 1)nscd iipoii something beyond mere natioiinl pride. I n hct, niieroscopcs: fiiiislictl by the most skilful opticians, have nrrivcd at a liigli clcpx of prrfection in nearly cvcry country, and difl'cr less t'lian is gciirrall y supposcd. During. the past teii years tlierc has becn grmt conipctition among opticians, but in every cmc tlicir progress liibs bccii arrested by one insarmountublc obstacle. Since tlie recent iiii1)rov-cnieiit in correcting the objectivcs for the tliickiicss of t'lic covcrglasses, comparatively little has been donc. Indeed it is alwnys stated and acc.ept.ed as a fact, that tlie proper iiieaiis of ohtailling a stronger power consists in securing a higher power of the objcctives and a smaller focal distance mitli greater angular qwrturc, and in this opticians have arrived at a rare clegrec of' perfcction. Objectives of ,l,th in. are made, and tho greatest aiigular apcrturc, so far as I know, is in the r'2th objective by Spenccr, with 1 7 7 angular aperture. But even here further progrcss is arrcstecl. Tlio increase of the angular aperture increases the two aberrations to bc corrected, and materially weakcris the penetrating power. Jndgiiig from an examination of tlie tcst-plate of Nobert, it wonld appear that the best instruments of any country differ but little in 11oivcr.