Transactions . o myopia is an important factor, perhaps one of the most im-portant factors, in the case, and that to the accurate opticalcorrection of the astigmatism, conjoined, as I think it shouldbe in many cases, with systeuiatic instillations of atropia, wemust chiefly look for the control of the pathological process. ON THE INCREASE OF REFEACTIVE POWER OF APLANO-CYLINDRICAL LENS WHEN ROTATED ABOUTITS AXIS. By Dr. G. Hay, Boston. In the ? diagram Fig. 1, let P be the middle of the anterior orcurved surface of the lens, and PM be a straight line in this surface(such line being parallel to
Transactions . o myopia is an important factor, perhaps one of the most im-portant factors, in the case, and that to the accurate opticalcorrection of the astigmatism, conjoined, as I think it shouldbe in many cases, with systeuiatic instillations of atropia, wemust chiefly look for the control of the pathological process. ON THE INCREASE OF REFEACTIVE POWER OF APLANO-CYLINDRICAL LENS WHEN ROTATED ABOUTITS AXIS. By Dr. G. Hay, Boston. In the ? diagram Fig. 1, let P be the middle of the anterior orcurved surface of the lens, and PM be a straight line in this surface(such line being parallel to the cyl. axis, and the tangent plane atthis line being parallel to the plane surface of the lens). Let OP,the axis of the obliquely incidentpencil, lie in a plane perpendicularto PM; this plane intersecting tlie curved surface of the lens in theline HP. Thus the lens may be more or less oblique to OP, but insuch a way that the latter is always perpendicular to PM, whichlast may be called the axis of the In considering the refraction of the homocentric pencil OPMH bythe oblique lens we find that after refraction it becomes astigmatic. The plane pencil OPH, in a plane perpendicular to the line arovindwhich the lens is rotated, remains after refraction in the same planeas before, and is refracted by the oblique lens in very nearly thesame way as a direct pencil would be by a lens of focal distance. f X 2 (n cos. cf>— COS. <^) [a]^ * For principles according to which formula [a] may be obtained, see Paark-insons Optics, London, 1870. .. - j 320 f being the focal distance of the cylindrical lens, the ang. of refraction corresponding to an angle of incidence ^, and n being the index of refraction, equal to , about. The values of formula [a] for f =100, and successive values of ,are given in a communication by Prof. E. C. Pickering and Dr. Williams, on the Foci of Lenses placed Obliquely, published inthe Proceedings of th
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