Dec. P7,1884}-tdPLCAL eP~}' _ __5._ have a most ,v4luable objective -test. By its,-means, we caio quickly, easily, and thbi6tigh1 examine the media a1 d the various parts 'of hte fundus oculi; we x.an a1o, without difficulty, determine the quality of any' error of refraction. believe, also, that' by prolonged practice some observers becdmne so -expert .that they ore able 'to calculate the amount 'f the,error'of refraction in any given meridi'it.i I regret to say, however, that in my experience,

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... -this hower of estimating the exact quantity of error has been extremely difficult to.acquire. The essential. rules'for this 'method are, (1) that the observer's eye shall be emmetropic, and.his accommodation recfed. (2.) That' in myopia the weakest concave lens with which the fundus can be clearly seen is the measure of the myopia. (3.) That in hypermetropia the strongest convex lens with which the fundus can be clearly'seen is-the measure of the hypermetropia.,-(4.) That in asti'mantism the refraction of either principal meridian may be a scertanid by finding the weakest concave or. the strongest .convex glass, with 'which vessels whose course is at right angles to that meridian can. be seen. Now, with regard to-the first of these requirements, I ,And it a very difficult matter to know where mny own -accommodation is* completely. relaxed. I' hm", therefore, uncertain as 'to' the estimation of the quantity either of mlyopia or of hypermetropia. With astigmatism I am still less certain, for here we' are obliged to examine, not the region of the yellow spot-which corresponds to the visual axis, but the region of the optic disc, from which vessels are radiating in several directions. I say, that owing to the paucity of visible blood v,ssels, in the imnmediate vicinity 'of the yeflow spot, I should be unable accurately' to estimate the amount of astigmatism even if ,I possessed the power of completely relaxi;ng my own accommodatin. I admit, however, that an expert" and I believe thereare xiany such, can often arrive at a very, close estirmate of the, refraction, even of an astigmatic eye; but I know, not only from 'my own experience, but from that of many students and practitioners with' whom Tam constantly working, that,thi,s is an accomplishment soiwewhat similar to that of playing, the violin ; it requires not onlyaptitude, but-prolonged and constant practice. To those who have thqroughly